other Edentates, their presumed affinity with the _Manidæ_ being more or
less problematical; but the discovery recently made by Mr. O. Thomas[115]
that they have a milk-dentition still further emphasises their aberrant
nature. According to this observer, it appears that there are normally
no less than seven milk-teeth in the upper jaw, the hindmost of which is
far larger than the others, having a rudimentary crown, and a distinct
anterior and posterior root. The other milk-teeth are styliform, the
four anterior ones being very minute, and separated from one another
by equal intervals; the foremost of all is situated immediately behind
the premaxillo-maxillary suture. In the mandible only four milk-teeth
have hitherto been detected, of which the hindmost has the comparatively
complex form found in the corresponding upper tooth. None of these
milk-teeth appear, however, to cut the gum, so that the whole set is
entirely functionless. Under the microscope these milk-teeth show signs
of possessing a commencement of the remarkable histological structure
found in the permanent teeth.
Mr. Thomas remarks that since “the three large posterior teeth of
_Orycteropus_, already distinguished by their more molariform shape, do
not have milk-predecessors, while all the small teeth anterior to them
do, and in addition the last milk-tooth is markedly different from those
in front of it, we ought apparently no longer to look upon this animal as
an homodont, but instead to consider it as an originally heterodont form
in which the incisors and canines have been suppressed to allow free play
to the mobile vermiform tongue.
“But important as a knowledge of the presence of a milk-dentition in
_Orycteropus_ is, it does not at present render any easier the difficult
questions as to the phylogeny and systematic position of that animal.
Although called an Edentate, it has always been recognised as possessing
many characters exceedingly different from those of the typical American
members of the order. It has in fact been placed with them rather on
account of the inconvenience of forming a special order for its reception
than because of its real relationship to them. Now, as they are either
altogether toothless, or else homodont and monophyodont (apart from the
remarkable exception of _Tatusia_), it seems more than ever incorrect
to unite with them the solitary member of the Tubulidentata, toothed,
heterodont, and diphyodont, and differing from them in addition by
its placentation, the anatomy of its reproductive organs, the minute
structure of its teeth, and the general characters of its skeleton.
“But if _Orycteropus_ is not genetically a near relation of the
Edentates, we are wholly in the dark as to what other mammals it is
allied to, and I think it would be premature to hazard a guess on the
subject. Whether even it has any special connection with _Manis_ is
a point about which there is the greatest doubt, and unfortunately
we are as yet absolutely without any palæontological knowledge of
the extinct allies of either. _Macrotherium_ even, usually supposed
from the structure of its phalangeal bones, to be related to _Manis_,
has lately proved to have the teeth and vertebræ of a perissodactyle
Ungulate, and one could not dare to suggest that ancestors of _Manis_,
or _Orycteropus_ were to be sought in that direction. Lastly, as the
numerous fossil American Edentates do not show the slightest tendency
to an approximation towards the Old World forms, we are furnished with
an additional reason for insisting on the radical distinctness of the
latter, whose phylogeny must therefore for the present remain one of the
many unsolved zoological problems.”
The Aard-Varks (Earth-Pigs) as these creatures are commonly termed,
from the name bestowed on them by the Dutch Boers of the Cape, are of
nocturnal habits, sleeping during the day in their burrows, which are
usually found in the neighbourhood of the tall hills or mounds made by
termites. Indeed, wherever these hills are abundant it is stated there
is a good chance of finding an Aard-Vark, the food of these animals
consisting almost exclusively of termites and ants.
Two existing species are recognised, namely the Cape Aard-Vark (_O.
afra_) from South Africa, and another (_O. æthiopicus_) from the
north-eastern parts of Africa, ranging into Egypt. An extinct species
has been described from the Lower Pliocene of the Isle of Samos, in the
Turkish Archipelago, differing from the existing forms by the larger
proportionate size of the lateral metatarsals.
_Bibliography of Edentata._—No general work on the order has
been published since that of Rapp (_Anat. Untersuchungen über
die Edentaten_, 2d ed. 1852). Among numerous memoirs on special
groups the following may be cited:—_Myrmecophagidæ_:—R. Owen,
“Anatomy of Great Anteater,” _Trans. Zool. Soc._ vol. iv.; G.
Pouchet, _Mém. sur le Grand Fourmilier_, 1874; W. A. Forbes,
“Anat. of Great Anteater,” _Proc. Zool. Soc._ 1882, p. 287.
_Megatheriidæ_:—R. Owen, _Extinct Gigantic Sloth (Mylodon
Robustus)_, 1842; Id., “On the Megatherium,” _Phil. Trans._
1851-56; J. Leidy, “Extinct Sloth-tribe of North America,”
_Smithsonian Contrib. to Knowledge_, vii. 1855; H. Burmeister,
_Description de la République Argentine_, t. iii. Mammifères,
1879,—which contains full references to various memoirs by
Owen, Gervais, Reinhardt, and others. _Glyptodontidæ_:—Owen,
_Catalogue of Fossil Mammals, Mus. Roy. Coll. Surgeons_, 1845;
T. H. Huxley, “Osteol. of Glyptodon,” _Phil. Trans._ 1865; H.
Burmeister, _Annales del Museo Publico de Buenos Aires_, and
_Descript. de la République Argentine_, 1879; H. Gervais and F.
Ameghino, _Les Mammifères Fossiles de l’Amérique Méridionale_,
Paris, 1880,—which also contains a list of all the S. American
Edentates described at that date. _Dasypodidæ_:—J. Murie,
“Anatomy of _Tolypeutes_,” _Trans. Linn. Soc._ vol. xxx. 1874;
A. H. Garrod, _Proc. Zool. Soc._ 1878. For Placentation of
Edentates see W. Turner, _Trans. Roy. Soc. Edin._ xxvii. (1873)
p. 72, and _Journ. Anat. and Physiol._ vols. viii. and x.; A.
Milne-Edwards, _Ann. Sciences Nat._ [6] viii. p. 1; and for
brain, P. Gervais, “Formes cérébrales des Edentés,” _Nouv.
Arch. du Muséum_, tom. v.; W. Turner, _Jour. Anatomy_, i. 313
(1867). For the dentition of _Orycteropus_ see O. Thomas, “A
Milk Dentition in _Orycteropus_,” _Proc. Roy. Soc._ vol. xlvii.
p. 246 (1890). Fuller observations on the mutual relations of
the various families are given by W. H. Flower, “On the Mutual
Affinities of the Animals composing the Order Edentata,” _Proc.
Zool. Soc._ 1882, p. 358.
CHAPTER VIII
THE ORDERS SIRENIA AND CETACEA
_Order_ SIRENIA.
The purely aquatic habits and fish-like form of the animals of this
order caused them to be formerly confounded with the Cetacea, but a more
intimate knowledge of their structure has shown that they really belong
to a widely different type of the mammalian class.
The head is rounded and not disproportionate in size as compared with
the trunk, from which it is scarcely separated by any externally visible
constriction or neck. Nostrils valvular, separate, and placed above
the fore part of the obtuse truncated muzzle. Eyes very small, with
imperfectly formed eyelids, capable, however, of contraction, and with
a well-developed nictitating membrane. Ear without any pinna. Mouth
of small or moderate size, with tumid lips beset with stiff bristles.
General form of the body depressed, fusiform. No dorsal fin. Tail
flattened and horizontally expanded. Fore limbs paddle-shaped, the digits
being enveloped in a common cutaneous covering, on which rudiments of
nails are sometimes present. No trace of hind limbs in existing forms.
External surface covered with a tough, finely wrinkled, or very rugose
skin, naked, or with fine hairs sparsely scattered over it.
The skeleton is remarkable for the massiveness and density of most of
the bones of which it is composed, especially the skull and ribs, which
must add to the specific gravity of these slow-moving animals, and
aid in keeping them to the bottom of the shallow waters in which they
dwell, while feeding on aquatic vegetables. The skull presents many
peculiarities, among which may be indicated the large size and backward
position of the anterior narial aperture, a further modification of that
met with in the Tapirs among Ungulates, and presenting some approach to
that so characteristic of the Cetacea. The nasal bones are generally
absent in the recent forms, or are only found in a most rudimentary
condition, attached to the edge of the frontals, far away from the
middle line; but in some at least of the extinct species these bones,
though small in size, are normal in situation and relations. In very few
other respects does the skull present any resemblance to that of the
Cetacea. In the spinal column of existing forms none of the vertebræ are
united together to form a sacrum, and the flat ends of the bodies do
not ossify separately, so as to form disc-like epiphyses in the young
state, as in nearly all other mammals; traces of epiphyses have, however,
been recently detected in _Manatus_, and they were fully developed in
_Halitherium_ and other fossil forms. The anterior caudal vertebræ have
well-developed chevron bones. In one genus (_Manatus_) there are only six
cervical vertebræ. There are no clavicles. The humerus has a small but
distinct trochlear articulation at the elbow-joint. The two bones of the
forearm are about equally developed, and generally ankylosed together
at both extremities. The carpus is short and broad, and the digits five
in number, with moderately elongated and flattened phalanges, which are
never increased in number beyond the limit usual in the Mammalia. The
pelvis is extremely rudimentary, consisting of a pair of bones suspended
at some distance from the vertebral column. In no existing species is
there any trace of a hind limb, but in the extinct _Halitherium_ an
acetabular depression and rudimentary femur have been discovered.
Two kinds of teeth, incisors and molars, separated by a wide interval,
are generally present. The former may be developed into tusks in
the upper jaw, or may be quite rudimentary. The molars vary much in
character. In one genus (_Rhytina_) no teeth of any kind are present, at
least in the adult. Some fossil forms show a more decidedly heterodont
dentition, while _Halitherium_ has milk-teeth, of which no traces have
been observed in the recent genera. In all recent types the anterior part
of the palate, and a corresponding surface on the prolonged symphysis
of the lower jaw, are covered with rough horny plates of peculiar
structure, which doubtless assist in mastication. The tongue is small
and fixed in position, with a surface resembling that of the plates just
spoken of. The salivary glands are largely developed. The stomach is
compound, being divided by a valvular constriction into two principal
cavities, the first of which is provided with a singular glandular pouch
near the cardiac end, and the second usually with a pair of elongated,
conical, cæcal sacs or diverticula. The intestinal canal is long, and
has very muscular walls. There is a cæcum, either simple, conical, and
with extremely thick walls, as in _Halicore_, or bifid, as in _Manatus_.
The heart is broad and flat, with its apex deeply cleft between the
ventricles. The principal arteries form very extensive and complex retia
mirabilia. The lungs are remarkably long and narrow, as, owing to the
very oblique position of the diaphragm, the thoracic cavity extends far
back over the abdomen. The epiglottis and arytenoid cartilages of the
larynx do not form a tubular prolongation as in the Cetacea, so that the
epiglottis is not intranarial. The brain is of comparatively small size,
and the convolutions on the surface of the cerebrum are few and shallow.
The kidneys are simple. The testes abdominal. The uterus is bicornuate.
The placenta (in the Dugong) is non-deciduate and zonary. The umbilical
vesicle disappears early. The mammæ are two, and pectoral, or rather
postaxillary in position.
The Sirenia pass their whole life in the water, being denizens of
shallow bays, estuaries, lagoons, and large rivers, but, unlike the
Cetacea, are not met with in the high seas, far away from the shore.
Their food consists entirely of aquatic plants, either marine algæ or
freshwater grasses, upon which they browse beneath the surface, as the
terrestrial herbivorous mammals do upon the green pastures on shore.
They are generally gregarious, slow and inactive in their movements,
mild, inoffensive, and apparently unintelligent in disposition.
Though occasionally found stranded by the tide or waves, there is no
satisfactory evidence that they voluntarily leave the water to bask or
feed on the shore. The habit of the Dugong of raising its round head
out of the water, and carrying its young under the fore fin, seems to
have given rise, among the imaginative early voyagers in the Indian
Ocean, to the legendary beings, half human and half fish, in allusion
to which the name Sirenia was bestowed by Illiger on the order, though
certainly the face of a Dugong, when closely inspected, does not bear the
slightest resemblance to that of the mermaid of romance. The species now
existing are very few, and there is reason to believe that the time is
not far distant when they will all become extinct. One species, _Rhytina
stelleri_, of the North Pacific, was totally exterminated through the
agency of man during the last century; and the others, being valuable for
their flesh as food, for their hides, and especially for the oil obtained
from the thick layer of fat which lies immediately beneath their skin,
rapidly diminish in numbers as civilised populations occupy the regions
forming their natural habitat. The surviving species are confined to the
tropical regions of the shores of both sides of the Atlantic and the
great rivers which empty themselves into that ocean, and to the coasts of
the Indian Ocean from the Red Sea to North Australia. In the Miocene and
early Pliocene epoch Sirenians abounded in the seas of Europe, and their
remains have been found in deposits of corresponding periods in North
America. Evidence has also been discovered of the existence of an animal
of this group in the seas at the bottom of which the Eocene nummulitic
limestone mountain ranges of Egypt were deposited.
The existing genera present such well-marked distinguishing characters
that it is on the whole convenient to place them in separate families,
although, as in so many similar cases, our knowledge of the extinct
forms, imperfect as it is, goes far to bridge over the distinction
between them.
_Family_ MANATIDÆ.
The characters of this and the two following families may be conveniently
included under the heading of the single genus by which they are
respectively represented.
_Manatus._[116]—Incisors ²⁄₂, rudimentary, concealed beneath the horny
oral plates, and disappearing before maturity. Molars ¹¹⁄₁₁, but rarely
more than ⁶⁄₆ present at one time, the anterior teeth falling before the
posterior come into use; similar in characters from beginning to end of
the series; with square, enamelled crowns, the grinding surface raised
into tuberculated transverse ridges. The upper teeth with two ridges
and three roots, the lower teeth with an additional (posterior) ridge,
or talon, and two roots. The cervical vertebræ present the remarkable
anomaly of being reduced to six in number, the usual vertebral formula
being C 6, D 17, L 2, and C 23-25. Rostrum of the skull, formed by
the union of the premaxillæ in front of the anterior narial aperture,
shorter than the length of the aperture and scarcely deflected from
the basicranial axis; premaxillæ and mandibular symphysis not markedly
deflected (Fig. 72). Tail entire, rounded, or shovel-shaped. Rudimentary
nails on the fore limbs. Cæcum bifid. Habitat the shores of, and the
great rivers which empty themselves into, the Atlantic within the
tropics. These animals are rather fluviatile than marine, ascending large
rivers almost to their sources.
The Manatee may be selected for a somewhat full description, as being one
of the best known representatives of this very remarkable order.
The name _Manati_ was apparently first applied to this animal by the
early Spanish colonists of the West Indies, in allusion to the hand-like
use which it frequently makes of its fore limbs; by English writers from
the time of Dampier (who gives a good account of its habits) downwards
it has been generally spelt “Manatee.” It was placed by Linnæus in his
heterogeneous genus _Trichechus_, but Storr’s name _Manatus_ is now
generally accepted for it by zoologists. The question of the specific
distinction of the African and American Manatees will be treated of
further on, but it will be chiefly to the latter and better known form
that the following description applies.
[Illustration: FIG. 71.—American Manatee (_Manatus americanus_), from
life. _Proc. Zool. Soc._ 1881, p. 457.]
The size of the Manatee has been much exaggerated, but there is no
trustworthy evidence of its attaining a greater length than 8 feet. Its
general external form may be seen in Fig. 71, taken from a living example
in the Brighton Aquarium. The body is somewhat fish-like, but depressed
and ending posteriorly in a broad, flat, shovel-like, horizontal tail,
with rounded edges. The head is of moderate size, oblong, with a blunt,
truncated muzzle, and divided from the body by a very slight constriction
or neck. The fore limbs are flattened oval paddles, placed rather low
on the sides of the body, and showing externally no signs of division
into fingers, but with a tolerably free motion at the shoulder, elbow,
and wrist joints, and with three diminutive flat nails near their
extremities. No traces of hind limbs are discernible either externally
or internally; and there is no dorsal fin. The mouth is very peculiar,
the tumid upper lip being cleft in the middle line into two lobes, each
of which is separately movable, as will be described in speaking of its
manner of feeding. The nostrils are two semilunar valve-like slits, at
the apex of the muzzle. The eyes are very minute, placed at the sides
of the head, and with a nearly circular aperture with wrinkled margins.
The external ear is a minute orifice situated behind the eye, without
any trace of pinna. The skin generally is of a dark grayish colour, not
smooth and glistening, like that of the Cetacea, but finely wrinkled. At
a little distance it appears naked, but a close inspection, at all events
in young animals, shows a scanty covering of very delicate hairs, and
both upper and under lips are well supplied with short stiff bristles.
[Illustration: FIG. 72.—Skull of African Manatee (_Manatus
senegalensis_). ⅕ natural size. From Mus. Roy. Coll. Surgeons.]
The general form of the skull is seen in Fig. 72. The cerebral cavity
is rather small as compared with the size of the animal, and of oblong
form; its roof is formed of the parietal bones as in ordinary mammals.
The squamosal has an extremely large and massive zygomatic process, which
joins the largely developed jugal bone in front. The orbit is small,
but prominent and nearly surrounded by bone. The anterior nares taken
together form a lozenge-shaped aperture, which looks upwards and extends
backwards considerably behind the orbits. Their sides are formed by the
ascending processes of the premaxillæ below, and by the supraorbital
processes of the frontals above, no traces of nasals being found in most
skulls, though these bones are occasionally present in a most rudimentary
condition, attached to the edges of the frontals, far away from the
middle line, in a position quite unique among the Mammalia. In front of
the narial aperture the face is prolonged into a narrow rostrum, formed
by the premaxillæ, supported below and at the sides by the maxillæ.
The under surface of this is very rugose, and in life covered by a
horny plate. The rami of the mandible are firmly united together at
the symphysis, which is compressed laterally, slightly deflected, and
has a rugose upper surface; to this another horny plate is attached,
which, with that of the upper jaw, functionally supplies the place of
teeth in the anterior part of the mouth. In the young state there are
rudimentary teeth concealed beneath these horny plates, which never
penetrate through them, and must therefore be quite functionless, and
altogether disappear before the animal is full-grown. There is besides
on each side of the hinder part of both upper and lower jaws, a parallel
row of molar teeth, similar in characters from the beginning to the end
of the series, with square enamelled crowns raised into tuberculated
transverse ridges; something like those of the Tapir and Kangaroo. The
upper teeth have two ridges and three roots; the lower teeth have an
additional posterior small ridge or talon, and but two roots. These teeth
succeed each other from before backwards, as in the Proboscidea, those
at the front of the mouth being worn out and shed before those at the
back are fully developed. There are altogether about eleven on either
side of each jaw, but rarely more than six are present at one time. The
brain is remarkably simple in structure, its hemispheres exhibiting none
of the richness of convolution so characteristic of the Cetacea. The
mammary glands of the female are situated just behind and to the inner
side of the origin of the pectoral limb. The red corpuscles of the blood
are among the largest of those of any members of the class, averaging in
diameter, according to Gulliver, ¹⁄₂₄₀₀ of an inch.
Manatees pass the whole of their life in the water, inhabiting bays,
lagoons, estuaries, and large rivers; but the open sea, so congenial
to the Cetacea, is quite unsuited to their peculiar mode of life. As a
general rule they prefer shallow water, in which, when not feeding, they
lie near the bottom, supporting themselves on the extremity of the tail,
or slowly moving about by the assistance of the fore limbs, the tips of
which are just allowed to touch the ground, and only raising the top of
the head above the surface for the purpose of breathing at intervals of
two or three minutes. In deeper water they often float, with the body
much arched, the rounded back close to the surface, and the head, limbs,
and tail hanging downwards. The air in the lungs obviously assists them
to maintain this position, acting in the same manner as that in the
air-sac of fishes. Their food consists exclusively of aquatic plants,
on which they browse beneath the water. They are extremely slow and
inactive in their movements, and perfectly harmless and inoffensive.
Frequent attempts have been made to keep specimens alive in captivity,
and sometimes with considerable success, one having lived in the Brighton
Aquarium for upwards of sixteen months. It was fed chiefly on lettuce
and endive, but would also eat leaves of the dandelion, sow-thistle,
cabbage, turnip, and carrot. From this and other captive specimens some
interesting observations upon the mode of life of the animal have been
made. One of these is the free use it makes of its fore limbs. From the
shoulder-joint, they can be moved in all directions, and the elbow and
wrist permit of free extension and flexion. In feeding these creatures
push the food towards their mouths by means of one of the hands, or both
used simultaneously, and any one who has seen these members thus employed
can readily believe the stories of their carrying their young about
under their arms. Still more interesting and quite unique among mammals
is the action of the peculiar lateral pads formed by the divided upper
lip, thus described by the late Professor Garrod: “These pads have the
power of transversely approaching towards and receding from one another
simultaneously (see Fig. 73, A and B). When the animal is on the point of
seizing (say) a leaf of lettuce, the pads are diverged transversely in
such a way as to make a median gap of considerable breadth. Directly the
leaf is within grasp the lip-pads are approximated, the leaf is firmly
seized between their contiguous bristly surfaces, and then drawn inwards
by a backward movement of the lower margin of the lip as a whole.” The
animal is thus enabled by the unaided means of the upper lip to introduce
food placed before it without the assistance of the comparatively
insignificant lower lip, the action greatly recalling to the observer
that of the mouth of the silkworm and other caterpillars, in which the
mandibles diverge and converge laterally during mastication. When out
of water the Manatee is an extremely helpless animal; and, although
statements are frequently met with in books of its voluntarily leaving
the water for the purpose of basking or feeding on shore, all trustworthy
observations of those acquainted with it, either in a state of nature or
in captivity, indicate that it has not the power of doing so. None of the
specimens in confinement have been observed to emit any sound.
[Illustration: FIG. 73.—Front view of head of American Manatee, showing
the eyes, nostrils, and mouth. A, With the lobes of the upper lip
divaricated; B, with the lip contracted. From Murie, _Trans. Zool. Soc._
vol. xi.]
Manatees, though much less numerous than formerly, are still occasionally
found in creeks, lagoons, and estuaries in some of the West India
Islands, and at various spots on the Atlantic coast of America from
Florida as far south as about 20° S. lat., and in the great rivers of
Brazil, almost as high as their sources. They are also met with in
similar situations on the opposite African coast, from about 16° N. to
10° S. lat., and as far into the interior as Lake Tchad. Their range may
even extend, if native reports obtained by Schweinfurth are correctly
interpreted, to the river Keebaly, 27° E. long.
A considerable number of specific names have been applied to the existing
Manatees, but according to the researches of Dr. Hartlaub[117] they
may be reduced to three species, distinguished from one another, among
other features, by the characters of the skull, and more especially the
relations of the nasals to the adjacent bones. Of these the American
Manatee may be known as _M. americanus_, although it has been described
under the names of _M. latirostris_, and _M. australis_. The African
Manatee (_M. senegalensis_) differs from the American species in the
following cranial characters: the anterior part of the rostrum is
shorter, shallower, and altogether smaller; the orbit is smaller; the
zygomatic process is more deep and massive; the jugal bone is deeper
from above downwards; the upper margin of the anterior nares is narrower
and with a smooth and rounded, instead of a thin and serrated, edge; the
upper surface of the frontal is flat, instead of concave; the foramen
magnum and occipital condyles are narrower from side to side, and the
symphysis of the mandible is smaller and shallower.
Finally, _M. inunguis_ is a fluviatile species confined to the Amazon and
Orinoco, which has been but recently fully brought under the notice of
zoologists.
_Family_ HALICORIDÆ.
_Halicore._[118]—In the upper jaw a pair of large, nearly straight,
tusk-like incisors, directed downwards and forwards, partially coated
with enamel. In the male they have persistent pulps, and bevelled cutting
edges, which project a short distance from the mouth, but in the female,
though they remain through life in the alveolar cavity, they are not
exserted, and, the pulp-cavity being filled with osteodentine, they soon
cease to grow (as in the female Narwhal). In the young there is also a
second small deciduous incisor on each side above. At this age there are
also beneath the horny plate which covers the anterior portion of the
mandible four pairs of slender conical teeth lodged in wide alveolar
depressions; these become absorbed before the animal reaches maturity.
The molars are usually ⁵⁄₅, sometimes ⁶⁄₆, altogether, but not all in
place at once, as the first falls before the last rises above the gum;
they are more or less nearly cylindrical in section (except the last,
which is compressed and grooved laterally), without distinction into
crown and root, increasing in size from before backwards, with persistent
pulps and no enamel. The summits of the crowns are tuberculated before
wearing, afterwards flattened or slightly concave. Skull with rostrum
formed by the union of the premaxillæ in front of the narial aperture,
longer than the aperture itself, bending downwards at a right angle with
the basicranial axis, and enclosing the sockets of the large incisor
tusks. Anterior part of the lower jaw bent down in a corresponding
manner. Vertebræ: C 7, D 18-19, L and C 30. Tail broadly notched in the
middle line, and with two pointed lateral lobes. No nails on the fore
limbs. Cæcum single.
The Dugongs are more distinctly marine in their habits than the Manatees,
feeding chiefly on sea-water algæ. They inhabit the shallow bays and
creeks of the Red Sea, east coast of Africa, Ceylon, islands of the Bay
of Bengal and the Indo-Malayan Archipelago (including the Philippines),
and the north coast of Australia, ranging from Barrow Reefs on the west
to Moreton Bay on the east. Although the distinctive characters are not
very obvious, they have been divided into three species, according to the
localities which they respectively inhabit:—_H. tabernaculi_ from the Red
Sea, _H. dugong_ from the Indian seas, and _H. australis_ from Australia.
The last-named has lately been the object of a regular “fishery,” chiefly
on account of its oil, which is peculiarly clear, limpid, and free from
disagreeable smell, and is said to have the same medicinal properties as
cod-liver oil. Although often stated in books to attain the length of 20
feet when adult, there does not appear to be any evidence from actual
specimens in museums that Dugongs ever reach half that size, 8 feet being
the common length of adult animals.
The placentation of this genus has been recently described by Sir W.
Turner, who first indicated its zonary form.
_Family_ RHYTINIDÆ.
_Rhytina._[119]—No teeth, their place being supplied functionally by the
dense, strongly-ridged, horny oral plates. Premaxillary rostrum about as
long as the anterior narial aperture, and moderately deflected. Vertebræ:
C 7, D 19, L and C 34-37. Head very small in proportion to the body. Tail
with two lateral pointed lobes. Pectoral limbs small and truncated. Skin
naked and covered with a very thick, hard, rugged, bark-like epidermis.
Stomach without cæcal appendages to the pyloric cavity. Cæcum simple.
Only one species of this genus is known, _R. stelleri_, the Northern
Sea-cow, by far the largest animal of the order, attaining the length of
20 to 25 feet. It was formerly an inhabitant of the shores of two small
islands in the North Pacific, Behring and the adjacent Copper Island,
on the former of which it was discovered by the ill-fated navigator
whose name the island bears, when, with his accomplished companion, the
German naturalist Steller, he was wrecked upon it in 1741. Twenty-seven
years afterwards (1768), as is commonly supposed, the last of the race
was killed,[120] and its very existence would have been unknown to
science but for the interesting account of its anatomy and habits left by
Steller, and the few more or less imperfect skeletons which have recently
rewarded the researches carried on in the frozen soil of the islands
around which it dwelt. There is no evidence at present of its having
inhabited any other coasts than those of the islands just named, although
it can hardly be supposed that its range was always so restricted. When
first discovered it was extremely numerous in the shallow bays round
Behring Island, finding abundant nutriment in the large laminariæ growing
in the sea. Its extirpation is entirely due to the Russian hunters and
traders who followed upon the track of the explorers, and, upon Steller’s
suggestion, lived upon the flesh of the great Sea-cows. Its restricted
distribution, large size, inactive habits, fearlessness of man, and even
its affectionate disposition towards its own kind when wounded or in
distress, all contributed to accelerate its final extinction.
According to Steller’s account, the Rhytina had a skin of a dark brown
colour, sometimes spotted or streaked with white. The fore limb was
covered with short brush-like hairs.
_Extinct_ SIRENIANS.
_Halitherium._[121]—The Miocene and early Pliocene seas of Europe
abounded in Sirenians, to which the generic name of _Halitherium_ was
given by Kaup, but which have also received other names. They had large
tusk-like incisors in the upper jaw, as in the existing Dugongs, though
not so greatly developed. Their molar teeth were ⁵⁄₅ or ⁶⁄₆, anteriorly
simple and single-rooted, posteriorly those above with three and those
below with two roots, and with enamelled and tuberculated or ridged
crowns, in all which respects they more resemble those of the Manatee
than of the Dugong. The anterior molars were deciduous; and there is
evidence of the presence of milk-teeth. Germs of inferior incisors were
also present. Some species at least had nasal bones, short, broad, but
normal in position, whereas in all the existing genera these bones
are quite rudimentary. Another and still more important evidence of
conformity to the general mammalian type is the better development of
the pelvic bone, and the presence of a small styliform femur articulated
to the acetabulum, although no traces of any other part of the limb
have been discovered. These ancient Sirenians, which may be regarded
as representing a distinct family—_Halitheriidæ_—were thus, in dental,
cranial, and other osteological characters, less specialised than are
either of the existing species, and if the intermediate links could be
discovered might well be looked upon as the ancestral forms from which
the latter have been derived, but at present the transitional conditions
have not been detected. So far as is yet known, when changes in the
physical conditions of the European seas rendered them unfitted to be the
habitation of Sirenians, the _Halitherium_ type still prevailed. If the
existing Dugongs and Manatees are descended from it, their evolution must
have taken place during the Pliocene and Pleistocene epochs, the one in
seas to the east, the other to the west of the African continent, which
has long formed a barrier to their intercommunication. _Halitherium_
remains have been found in many parts of Germany, especially near
Darmstadt, also in France, Italy, Belgium, Malta, etc. Until a few years
ago none were known from England, probably owing to the absence of beds
of an age corresponding to those in which they are found on the European
continent; but a skull and several teeth have been detected among the
rolled debris of which the Red Crag of Suffolk is partially composed. The
species are not yet satisfactorily characterised. Some of them appear
to have attained a larger size than the existing Manatee or Dugong. One
of these, from the Pliocene of Italy and France, having but ⁵⁄₅ molar
teeth, has been separated generically under the name of _Felsinotherium_
by Capellini, by whom it has been fully described; but the difference in
the number of the teeth does not afford sufficient grounds for separation
from _Halitherium_. _Miosiren_ of the Belgian Miocene, differs in that
the last upper molar is the smallest, in place of the largest of the
whole series of teeth.
[Illustration: FIG. 74.—The penultimate and last right lower molars of
_Halitherium fossile_; from the Miocene of the Continent. (After De
Blainville.)]
_Other forms._—Remains from the Pliocene of France described as
_Prohalicore_ are regarded as indicating a Sirenian closely allied to
_Halicore_; while a molar from the Tertiary of California has been made
the type of _Desmotylus_, which is likewise referred to the _Halicoridæ_.
_Dioplotherium_, from the Phosphorites of South Carolina, has been
considered to connect _Halicore_ with _Halitherium_, but even its ordinal
position is uncertain.
A portion of a skull found in the Pliocene of Belgium has been described
as _Crassitherium_ by Van Beneden; and some compressed teeth, somewhat
similar to but larger than those of the Dugong, discovered in the Miocene
of the department of Lot-et-Garonne, France, gave origin to the genus
_Rytiodus_ of E. Lartet. Of this genus, which may be identical with
_Trachytherium_ of the French Miocene, better preserved remains have
subsequently been described by Delfortrie. These show that the rostrum
is more elongated than in _Halitherium_, but the skull is otherwise very
similar, as are the molar teeth. The incisors are very large, exserted,
strongly compressed, almost sabre-like, rounded on the upper or anterior
surface, sharp below, concave on the external and convex on the inner
side, and transversely striated.
_Pachyacanthus_ from the Miocene of the Vienna basin is also, according
to Van Beneden, another form of Sirenian, of which, however, the skull
is not known. In various Miocene marine formations of the United States
of America other remains of Sirenians have been found, but mostly in
such a fragmentary condition that they afford at present little evidence
of the early history of the group in that country. A more satisfactory
discovery is that of a nearly complete skull and some bones from a
Tertiary limestone formation in Jamaica. It is of smaller size than
the Manatee, and, so far as the teeth are concerned, of a still more
generalised character than _Halitherium_, the dentition being apparently
_i_ ³⁄₃, _c_ ¹⁄₁, _p_ + _m_ (?⁸⁄?₈) = 48. The incisors are small, not
developed into tusks; the canines (wanting in all existing Sirenians)
are rather larger than the incisors, judging by the sockets; and the
molars are bilophodont, and covered with enamel. It has been described
by Sir R. Owen under the name of _Prorastomus sirenoides_. Some writers
regard this genus as the type of a distinct family—the _Prorastomatidæ_.
Unfortunately we have no knowledge of the geological antiquity of
the formation in which it was embedded. Lastly must be mentioned the
_Eotherium egyptiacum_, Owen, founded on the cast of a brain, with
a small quantity of surrounding bone, discovered in the nummulitic
limestone of Eocene age in the Mokattam Hills, near Cairo. The brain is
narrower than in _Manatus_, and resembles that of _Halitherium_. This is
of interest as the most ancient known evidence of any Sirenian whose age
has been geologically determined. Teeth from the same deposits referred
to _Manatus_ not improbably belong really to _Eotherium_.
The few facts as yet collected relating to the former history of the
Sirenia leave us as much in the dark as to the origin and affinities of
this peculiar group of animals as we were when we only knew the living
members. They lend no countenance to their association with the Cetacea,
and on the other hand their supposed affinity with the Ungulata, so much
favoured by modern zoologists, receives no very material support from
them.
_Bibliography of Sirenia._—J. F. Brandt, _Symbolæ
Sirenologicæ_, St. Petersburg, 3 fasciculi, 1846-61-68—an
exhaustive account of the anatomy, affinities, and literature
of the group, with copious illustrations of the osteology of
_Rhytina_. _Anatomy of Dugong_:—Everard Home, _Phil. Trans._
1820, p. 315; Owen, _Proc. Zool. Soc._ 1838, p. 29. _Placenta
of do._:—W. Turner, _Trans. Roy. Soc. Edin._ vol. xxxv.
(1889). _Manatee_:—W. Vrolik, _Bijdragen tot de Dierkunde_,
1851; J. Murie, “On the Form and Structure of the Manatee,”
_Trans. Zool. Soc. Lond._ vol. viii. p. 127, 1872, and “Further
Observations on the Manatee,” _Ibid._ vol. xi. p. 19, 1880;
A. H. Garrod, “Notes on the Manatee recently living in the
Zoological Society’s Gardens,” _Ibid._ vol. x. p. 137, 1875;
H. C. Chapman, “Observations on the Structure of the Manatee,”
_Proc. Acad. Nat. Sciences of Philadelphia_, 1875, p. 452; A.
Crane, “Notes on the Habits of the Manatees in Captivity in
the Brighton Aquarium,” _Proc. Zool. Soc. Lond._ 1881, p. 456.
_Extinct Sirenia_:—Gervais, _Journal de Zoologie_, tom. i. p.
332, 1872. R. Lydekker, _Catalogue of Fossil Mammalia in the
British Museum_, pt. v.
_Order_ CETACEA.
This is perhaps the most distinctly circumscribed and natural of all the
larger groups into which the class is divided.
The external form is fish-like, the body being fusiform, passing
anteriorly into the head without any distinct constriction or neck, and
posteriorly tapering off gradually towards the extremity of the tail,
which is provided with a pair of lateral, pointed expansions of skin
supported by dense fibrous tissue, called “flukes,” forming together a
horizontally-placed triangular propelling organ, notched in the middle
line behind.
The head is generally large, in some species attaining to even more
than one-third of the entire length of the animal, and the aperture of
the mouth is always wide, and bounded by stiff immobile lips. The fore
limbs are reduced to the condition of flattened ovoid paddles, encased
in a continuous integument, showing no external sign of division into
arm, fore arm, and manus, or of separate digits, and without any trace
of nails. There are no traces of hind limbs visible externally. The
general surface of the skin is smooth and glistening, and devoid of
hair, although in many species there are a few fine bristles in the
neighbourhood of the mouth, which may either persist through life, or
be present only in the young state. Immediately beneath the skin, and
intimately connected with it, is a thick layer of fat, held together
by a dense mesh of areolar tissue, constituting the “blubber,” which
serves the purpose of the hairy covering of other mammals in retaining
the heat of the body. In nearly all species a compressed median dorsal
tegumentary fin is present. The eye is small, and is not provided with a
nictitating membrane or true lachrymal apparatus. The external auditory
meatus is a very minute aperture in the skin situated at a short distance
behind the eye, and there is no vestige of a pinna. The nostrils open
either separately or by a single crescentic valvular aperture, not at the
extremity of the snout, but near the vertex of the head.
The bones generally are spongy in texture, the cavities being filled with
oil. In the vertebral column the cervical region is remarkably short and
immobile, and the vertebræ, originally always seven in number, are in
many species more or less fused together into a solid mass. The odontoid
process of the axis, when that bone is free, is usually very obtuse, or
even obsolete. None of the vertebræ are united together to form a sacrum.
The lumbar and caudal vertebræ are numerous and large, and, as their
arches are not connected by any articular processes (zygapophyses), they
are capable of a very free motion in all directions. The epiphyses at
the ends of the vertebral bodies are very distinct flattened disks, not
uniting until after the animal has attained its full dimensions.[122]
There are largely developed chevron bones, the presence of which
indicates the distinction between the caudal and lumbar vertebræ.
The skull (Fig. 75) is modified in a very peculiar manner. The brain-case
is short, broad, and high, in fact almost spherical. The supraoccipital
bone rises upwards and forwards from the foramen magnum, to meet the
frontals at the vertex, thus completely excluding the parietals from the
upper region of the cranium. The frontals are expanded laterally to form
the roof of the orbits. The anterior narial aperture opens upwards, and
has in front of it a more or less horizontally prolonged rostrum, formed
of the maxillæ, premaxillæ, vomer, and mesethmoid cartilage, extending
forwards to form the upper jaw or roof of the mouth.
There are no clavicles. The humerus is freely movable on the scapula
at the shoulder-joint, but beyond this the articulations of the limb
are imperfect, the flattened ends of the bones coming in contact with
each other, with fibrous tissue interposed, allowing of scarcely any
motion. The radius and ulna are distinct, about equally developed,
and much flattened, as are also all the bones of the manus. There are
four, or more commonly five digits, and the number of the phalanges
of the second and third digits always exceeds the normal number in
mammals, sometimes very considerably (hyperphalangism); they present the
exceptional character of having epiphyses at both ends.[123] The pelvis
is represented by a pair of small styliform bones placed longitudinally,
suspended below and at some distance from the vertebral column at the
commencement of the caudal region. These appear to represent the ischia,
as the crura of the corpora cavernosa are attached to them. In some
species, to the outer surface of these are fixed other small bones or
cartilages, the rudiments of the hind limb.
[Illustration: FIG. 75.—A section of the skull of a young Dolphin
(_Globicephalus melas_) × ⅕. _PMx_, Premaxilla; _Mx_, maxilla; _ME_,
ossified portion of the mesethmoid; _an_, anterior nares; _Na_, nasal;
_IP_, interparietal; _Fr_, frontal; _Pa_, parietal; _SO_, supraoccipital;
_ExO_, exoccipital; _BO_, basioccipital; _Sq_, squamosal; _Per_,
periotic; _AS_, alisphenoid; _PS_, presphenoid; _Pt_, pterygoid; _pn_,
posterior nares; _Pl_, palatine; _Vo_, vomer; _s_, symphysis of mandible;
_id_, inferior dental canal; _cp_, coronoid process of mandible; _cd_,
condyle; a, angle; sh, stylohyal; _bh_, basihyal; _th_, thyrohyal. (From
Flower’s _Osteology of Mammalia_.)]
Teeth are generally present, but exceedingly variable in number. In
the existing species they are of simple, uniform character, all having
conical or compressed crowns and single roots, and are never preceded
by milk-teeth. They are therefore homodont and monophyodont. In one
group, the Mystacocetes, the teeth are absent (except, in the fœtal
condition), and the palate is provided with numerous transversely placed
horny laminæ or “baleen.” The salivary glands are rudimentary or absent.
The stomach is multilocular, its structure being fully noticed under
the genus _Phocæna_. The intestinal canal is simple, and only in some
species provided with a small cæcum. The liver is very little fissured,
and there is no gall-bladder. The vascular system is greatly complicated
by arterial and venous plexuses, or _retia mirabilia_. The larynx is of
peculiar shape, the arytenoid cartilages and the epiglottis being much
elongated, and together forming a tubular prolongation, which projects
into the posterior nares, and when embraced by the soft palate produces a
continuous passage between the nostrils and the trachea, as in Ungulates,
but in a more perfect manner. The brain is large relatively to the size
of the animal, very round in form, and with its surface divided by sulci
into very numerous and complex convolutions. The kidneys are deeply
lobulated. The testes are abdominal. There are no vesiculæ seminales,
nor os penis. The uterus is bicornuate, and the placenta non-deciduate
and diffuse. The mammæ are two in number, and the nipples placed in
depressions on each side of the vulva. The principal ducts of the gland
are dilated during lactation into large reservoirs, into which the milk
collects, and from which it is injected by the action of a compressor
muscle into the mouth of the young animal, by which means the process of
sucking under water is greatly facilitated and expedited.
The animals of the order Cetacea abound in all known seas, and some
species are inhabitants of the larger rivers of South America and Asia.
Their organisation necessitates passing their life entirely in the
water, as on land they are absolutely helpless. They have, however, to
rise very frequently to the surface for the purpose of respiration; and,
in relation to the constant upward and downward movement in the water
thus necessitated, their principal instrument of motion, the tail, is
expanded horizontally, quite unlike that of a fish, whose movements
are mainly in straight-forward or lateral directions. The position of
the respiratory orifice or nostril on the highest part of the head is
very important for this mode of life, since it is the only part of the
body of which the exposure above the surface is absolutely necessary.
Of the numerous erroneous ideas connected with natural history, few are
so wide spread and still so firmly believed, notwithstanding repeated
expositions of its falsity, as that the Cetacea spout out through their
blowholes water taken in at the mouth. The fact is, the “spouting,” or
more properly “blowing,” of the Whale is nothing more than the ordinary
act of expiration, which, taking place at longer intervals than in land
animals, is performed with a greater amount of emphasis. The moment the
animal rises to the surface it forcibly expels from its lungs the air
taken in at the last inspiration, which of course is highly charged with
watery vapour in consequence of the natural respiratory changes. This,
rapidly condensing in the cold atmosphere in which the phenomenon is
generally observed, forms a column of steam or spray, which has been
erroneously taken for water. It also often happens, especially when the
surface of the ocean is agitated into waves, that the animal commences
its expiratory puff before the orifice has quite cleared the top of
the water, some of which may thus be driven upwards with the blast,
tending to complete the illusion. In hunting Whales the harpoon often
pierces the lungs or air passages of the unfortunate victim, and then
fountains of blood may be forced high in the air through the blowholes,
as commonly depicted in scenes of Arctic adventure; but this is nothing
more (allowance being made for the Whale’s peculiar mode of breathing)
than what always follows severe wounds of the respiratory organs of other
mammals.
All the Cetacea are predaceous, subsisting on living animal food of
some kind. One genus alone (_Orca_) eats other warm-blooded animals, as
Seals, and even members of its own order, both large and small. Some feed
on fish, others on small floating crustaceans, pteropods, and medusæ,
while the principal staple of the food of many is constituted by the
various species of cephalopods, _Loligo_ and other _Teuthidæ_, which must
abound in certain seas in vast numbers, as they form almost the entire
support of some of the largest members of the order. In size the Cetacea
vary much, some of the smaller Dolphins scarcely exceeding 4 feet in
length, while others are the most colossal of all animals. It is true
that most statements of their bulk found in general and even zoological
literature are greatly exaggerated, but even when reduced to their actual
dimensions (which will be stated under the respective genera) some of
the existing Whales exceed in size any animal living either at present
or in former times of which we have any certain evidence. With some
exceptions, the Cetacea generally are timid inoffensive animals, active
in their movements, and very affectionate in their disposition towards
one another, especially the mother towards the young, of which there is
usually but one, or at most two at a time. They are generally gregarious,
swimming in herds or “schools” (so termed by the whalers) sometimes
amounting to many thousands in number; though some species have hitherto
only been met with either singly or in pairs.
Although by their mode of life so far removed from close observation
that it is impossible to become as familiar with them in their natural
condition as with many other animals, Whales are in many respects the
most interesting and wonderful of all creatures; and there is much in
their structure and habits well worthy of study, much that is difficult
to understand, and much that leads to great generalisations and throws
light upon far-reaching philosophical speculations. One of the first
lessons which a study of these animals affords is that, in the endeavour
to discover what a creature really is, from what others it is descended,
and to what it is related, the general outward appearance affords little
clue, and we must go deep below the surface to find out the essential
characteristics of its nature. There was once, and may be still in many
places, a common idea that a Whale is a fish. To realise the fallacy of
this notion we have only to consider what a fish really is, what under
all the diversities of form, size, and colour known among fishes there is
common to them all, and we see that in everything which characterises a
true fish and separates it from other classes, as reptiles, birds, and
mammals, the Whale resembles the last-named and differs from the fish.
It is as essentially a mammal as a Cow or a Horse, and simply resembles
a fish externally because it is adapted to inhabit the same element;
but it is no more on that account a fish than is a bat, because adapted
to pass a great part of its existence on the wing in the air, nearly
related to a bird. The whole structure of a whale is a most instructive
instance of a type of organisation which is common to and characteristic
of the class Mammalia, but specially modified or adapted to a peculiar
mode of life. We see in every part the result of two great principles
acting and reacting upon each other—on the one hand, adherence to type,
or rather to fundamental inherited structural conditions, and, on the
other, adaptation to the peculiar circumstances under which it lives, and
to which in all probability it has become gradually more and more fitted.
The external fish-like form is perfectly suited for swimming through
the water; the tail, however, is not placed vertically as in fishes,
but horizontally, a position which accords better with the constant
necessity for rising to the surface for the purpose of breathing. The
hairy covering characteristic of all mammals, which if present might
interfere with rapidity of movement through the water, is reduced to the
merest rudiments—a few short bristles about the chin or upper lip—which
are often only present in very young animals; and the function of keeping
the body warm is supplied by the “blubber.” The forelimbs, though
functionally reduced to mere paddles, with no power of motion except at
the shoulder-joint, have beneath their smooth and continuous external
covering all the bones, joints, and even most of the muscles, nerves, and
arteries of the human arm and hand; and the rudiments of hind legs found
buried deep in the interior of the animal apparently subserve no useful
purpose, but point an instructive lesson to those who are able to read it.
As before said, the Cetacea form a perfectly well-defined group, sharply
separated from all other mammals, and with no outlying or doubtful
forms at present known. Among the existing members of the order, there
are two very distinct types, the Toothed Whales or Odontoceti and the
Baleen Whales or Mystacoceti, which present as many marked distinguishing
structural characters as are found between many other divisions of the
Mammalia which are reckoned as orders. The extinct _Zeuglodon_, so far
as its characters are known, does not fall into either of these groups,
but is in some respects an annectant form, and therefore must be placed,
provisionally at least, in a third group by itself.
The Mystacocetes appear at first sight to be the most specialised and
aberrant of the existing Cetacea, as indicated by the absence of teeth,
the presence of baleen, and the form and size of the mouth; but, as we
see in other groups, dental characters, and all such as relate to the
prehension of food generally, are essentially adaptive and consequently
plastic or prone to variation, and hence cannot well be relied upon
as tests of affinity. In another character, also adaptive, the laxity
of the connection of the ribs with the vertebral column and with the
sternum, and the reduction of that bone in size, allowing great freedom
of expansion of the thoracic cavity for prolonged immersion beneath
the water, the Mystacocetes have passed beyond the Odontocetes in
specialisation. On the other hand, the greater symmetry of the skull, the
more anterior position of the external nostrils and their double external
orifice, the form of the nasal bones, the presence of a distinctly
developed olfactory organ, the mode of attachment of the periotic bone to
the cranium, the presence of a cæcum and the regular arrangement of the
alimentary canal, the more normal characters of the manus and the better
development of the muscles attached to it, and the presence, in many
species at least, of parts representing not only the bones but also the
ligaments and muscles of a hind limb,[124] all show less deviation from
the ordinary mammalian type than is presented by the Odontocetes. Taking
all these characters into consideration, it does not appear reasonable to
suppose that either type has been derived from the other, at all events
in the form in which we see it now, but rather that they are parallel
groups, both modified in different fashions from common ancestors.
Among the Mystacocetes, in the especially distinguishing characters of
the division, the Rorquals are less specialised than the Right Whales,
which in the greater size of the head, the length and compression of the
rostrum, the development of the baleen, and shortness of the cervical
region, are exaggerated forms of the type, and yet they retain more fully
some primitive characters, as the better development of the hind limb,
the pentadactylous manus, and the absence of a dorsal fin. Both types
are found distinct in a fossil state at least as far back as the early
Pliocene age, but generally represented by smaller species than those
now existing. Some of the Pliocene Rorquals (_Cetotherium_) were, in
the elongated flattened form of the nasal bones, the greater distance
between the occipital and frontal bone at the top of the head, and the
greater length of the cervical vertebræ, more generalised than those
now existing. In the shape of the mandible also, Van Beneden, to whose
researches we are much indebted for a knowledge of these forms, discerns
some approximation to the Odontocetes.
Among the last-named group there are several distinct types, of which
that represented by _Platanista_, although in some respects singularly
modified, has been considered to present on the whole approximations
towards the more normal and general type of mammalian structure. It is
therefore interesting to find an apparently allied form well represented
among the earliest fossil remains of Cetaceans in Europe. Almost all the
other members of the suborder range themselves under the two principal
heads of Ziphioids (or Physeteroids) and Delphinoids. The former is an
ancient and once abounding type, of which the Sperm Whale (_Physeter_)
is a highly specialised form. Among the latter, _Globicephalus_ is a
modified form as regards the structure of its anterior extremity, and
_Monodon_ as regards its dentition, while _Delphinus_, with the various
allied genera, may be regarded as the dominating type of Cetaceans at
the present day, abundant in slightly differentiated species and also in
individuals. They are in this respect to the rest of the order much as
the hollow-horned Ruminants are to the other Ungulates.
The earliest Cetaceans of whose organisation we have anything like
complete evidence are the Zeuglodonts of the Eocene period,[125]
which approach in the structure of the skull and teeth to a much more
generalised mammalian type than either of the existing suborders. The
smallness of the cerebral cavity compared with the jaws and the rest
of the skull they share with the primitive forms of many other types.
The forward position of the narial aperture and the length and flatness
of the nasal bones, which distinguish them from all existing forms, we
must also suppose to be a character at one time common to all Cetaceans,
though now retained (but to a less degree) only by the Mystacocetes.
Even _Squalodon_, which in its heterodont dentition so much resembles
_Zeuglodon_ as to have been placed by some zoologists in the same genus,
entirely differs from it, and conforms with the ordinary Dolphins in its
essential cranial characters.
The origin of the Cetacea is at present involved in much obscurity.
They present no signs of closer affinity to any of the lower classes of
vertebrates than do many other members of their own class. Indeed in all
that essentially distinguishes a mammal from the oviparous vertebrates,
whether in the osseous, nervous, reproductive, or any other system,
they are as truly mammalian as any other group. Any supposed marks
of inferiority, as absence of limb structure, of hairy covering, of
lachrymal apparatus, etc., are obviously modifications (or degradations,
as they may be termed) in adaptation to their special mode of life. The
characters of the teeth of _Zeuglodon_ and other extinct forms, and
also of the fœtal Mystacocetes, clearly indicate that they have been
derived from mammals in which the heterodont type of dentition was fully
established. The steps by which a land mammal may have been modified
into a purely aquatic one are indicated by the stages which still
survive among the Carnivora in the _Otariidæ_ and in the true Seals. A
further change in the same direction would produce an animal somewhat
resembling a Dolphin; and it has been thought that this may have been
the route by which the Cetacean form has been developed. There are,
however, great difficulties in the way of this view. Thus if the hind
limbs had ever been developed into the very efficient aquatic propelling
organs they present in the Seals, it is not easy to imagine how they
could have become completely atrophied and their function transferred to
the tail. So that from this point of view it is more likely that Whales
were derived from animals with long tails, which were used in swimming,
eventually with such effect that the hind limbs became no longer
necessary. The powerful tail, with its lateral cutaneous flanges, of an
American species of Otter (_Lutra brasiliensis_) may give an idea of this
member in the primitive Cetaceans. But the structure of the Cetacea is,
in so many essential characters, so unlike that of the Carnivora that
the probabilities are against these orders being nearly related. Even in
the skull of the Zeuglodon, which has been cited as presenting a great
resemblance to that of a Seal, quite as many likenesses may be traced to
one of the primitive Pig-like Ungulates (except in the purely adaptive
character of the form of the teeth), while the elongated larynx,[126]
complex stomach, simple liver, reproductive organs both male and female,
and fœtal membranes of the existing Cetacea are far more like those
of that group than of the Carnivora. Indeed it appears probable that
the old popular idea which affixed the name of “Sea-Hog”[127] to the
Porpoise contains a larger element of truth than the speculations of many
accomplished zoologists of modern times. The fact that _Platanista_,
which, as mentioned above, appears to retain more of the primitive
characteristics of the group than any other existing form, and also the
somewhat related _Inia_ from South America, are both at the present day
exclusively fluviatile, may point to the freshwater origin of the whole
group, in which case their otherwise rather inexplicable absence from the
seas of the Cretaceous period would be accounted for.
On the other hand, it should be observed that the teeth of the
Zeuglodonts approximate more to a carnivorous than to an ungulate type.
It is scarcely necessary to allude to the hypothesis started by some
Continental writers to the effect that the Whales are the most primitive
type of mammals with which we are acquainted, and that they are the
descendants of the Mesozoic reptilian order Ichthyopterygia, from which
their hyperphalangism is a direct inheritance. The Ichthyopterygia have
been shown, on very strong evidence, to have been derived from land
reptiles, and to have gradually acquired their hyperphalangism as an
adaptive character suitable to their peculiar mode of life, and there can
be but little doubt that a similar adaptation has taken place in the case
of the Whales.
_Suborder_ MYSTACOCETI, _the_ BALÆNOIDEA, _Whalebone, or True
Whales_.[128]
_Family_ BALÆNIDÆ.
Teeth never functionally developed, but always disappearing before the
close of intra-uterine life. Palate provided with plates of baleen
or “whalebone.” Skull symmetrical. Nasal bones forming a roof to the
anterior nasal passages, which are directed upwards and forwards.
Maxilla produced in front of, but not over, the orbital process of the
frontal. Lachrymal bones small and distinct from the jugal. Tympanic
bone involuted (Fig. 76), and ankylosed with the periotic, which is
attached to the base of the cranium by two strong diverging processes.
Olfactory organ distinctly developed. Rami of mandible arched outwards,
their anterior ends meeting at an angle, and connected by fibrous tissue
without any true symphysis. All the ribs at their upper extremities
articulating only with the transverse processes of the vertebræ; their
capitular processes, when present, not articulating directly with
the bodies of the vertebræ. Sternum composed of a single piece, and
articulating only with a single pair of ribs. No ossified sternal ribs.
External openings of nostrils distinct from each other, longitudinal. A
short conical cæcum.
These animals have, when in the fœtal state, numerous minute calcified
teeth lying in the dental groove of both upper and lower jaws. They are
best developed about the middle of fœtal life, after which period they
are absorbed, and no trace of them remains at the time of birth.[129] The
baleen or whalebone does not make its appearance until after birth. It
consists of a series of flattened horny plates, between three and four
hundred in number, on each side of the palate, with a bare interval along
the middle line. These plates are placed transversely to the long axis of
the palate, with very short intervals between them. Each plate or blade
is somewhat triangular in form, with the base attached to the palate
and the apex hanging downwards. The outer edge of the blade is hard and
smooth; but the inner edge and apex fray out into long bristly fibres,
so that the roof of the Whale’s mouth looks as if covered with hair, as
described by Aristotle. At the inner edge of each principal blade are
two or three much smaller or subsidiary blades. The principal blades are
longest near the middle of the series, and gradually diminish towards the
front and back of the mouth. The horny plates grow from a dense fibrous
and highly vascular matrix, covering the palatal surface of the maxillæ,
and sending out lamellar processes, one of which penetrates the base of
each blade. Moreover, the free edge of these processes is covered with
very long vascular thread-like papillæ, one of which forms the central
axis of each of the hair-like epidermic fibres of which the blade is
mainly composed. A transverse section of fresh whalebone shows that it is
made up of numbers of these soft vascular papillæ, circular in outline,
each surrounded by concentrically arranged epidermic cells, and the whole
bound together by other epidermic cells, that constitute the smooth
cortical (so-called “enamel”) surface of the blade, which, disintegrating
at the free edge, allows the individual fibres to become loose and
assume the hair-like appearance before spoken of. These fibres differ
from hairs in not being formed in depressed follicles in the enderon,
but rather resemble the fibres composing the horn of the Rhinoceros.
The whalebone in fact consists of nothing more than modified papillæ of
the buccal mucous membrane, with an excessive and cornified epithelial
development. The blades are supported and bound together for a certain
distance from their base by a mass of less hardened epithelium, secreted
by the surface of the palatal membrane or matrix of the whalebone in
the intervals of the lamellar processes. This is the “intermediate
substance” of Hunter, the “gum” of the whalers. Baleen varies much in
colour in different species. In some it is almost jet black, in others
slate-colour, horn-colour, yellow, or even creamy-white. In some the
blades are variegated with longitudinal strips of different hues. Baleen
differs also greatly in other respects, being short, thick, coarse, and
stiff in some, and greatly elongated and highly elastic in those species
in which it has attained its fullest development. Its function is to
strain the water from the small marine molluscs, crustaceans, or fish
upon which the Whales subsist. In feeding the immense mouth is filled
with water containing shoals of these small creatures, and then, on the
Whale closing the jaws and raising the tongue, so as to diminish the
cavity of the mouth, the water streams out through the narrow intervals
between the hairy fringe of the whalebone blades, and escapes through the
lips, leaving the living prey to be swallowed.[130]
Our knowledge of the different structural modifications attained by
members of this important group of mammals, though largely increased
of late years, is still imperfect. Formerly they were all divided into
Right Whales (_Balæna_) and Rorquals or Fin-Whales (_Balænoptera_), the
latter distinguished by their smaller heads, elongated and slender form,
free cervical vertebræ, tetradactylous manus, and the presence of very
conspicuous longitudinal furrows or folds in the skin of the throat
and chest, and of a small adipose dorsal fin. Recent discoveries have,
however, brought to light several forms holding a somewhat intermediate
position, and presenting combinations of characters not found in either
of the longer known sections. According to our present knowledge the
group is naturally divided into five very distinct genera, of which the
leading characters are given below.
_Balæna._[131]—Skin of throat smooth, not furrowed. No dorsal fin.
Cervical vertebræ united into a single mass. Pectoral limb short, broad,
and pentadactylous. Head very large. Baleen very long and narrow, highly
elastic, and black. Scapula high, with a distinct coracoid and acromion
process. Tympanic (Fig. 78) deep and angular, its inflation comparatively
slight, and the involuted portion not fig-shaped, and frequently without
a well-marked depression at the anterior extremity of the superior border
of the inner surface for the Eustachian canal.
[Illustration: FIG. 76.—Greenland or Arctic Right Whale (_Balæna
mysticetus_).]
The Greenland, or more properly Arctic, Right Whale (_Balæna mysticetus_)
attains, when full grown, a length of from 45 to 50 feet. Its usual
vertebral formula is C 7, D 12, L 14, C 22. The external form is shown
in Fig. 76 from a careful drawing by Mr. Robert Gray. In this species
all the peculiarities which distinguish the head and mouth of the Whales
from those of other mammals have attained their greatest development.
The head is of enormous size, exceeding one-third of the whole length
of the creature. The cavity of the mouth is actually larger than that
of the body, thorax and abdomen together. The upper jaw is very narrow,
but greatly arched from before backwards, to increase the height of the
cavity and allow for the great length of the baleen blades; the rami of
the mandible are widely separated posteriorly, and have a still further
outward sweep before they meet at the symphysis in front, giving the
floor of the mouth the shape of an immense spoon. The baleen blades
attain the number of 380 or more on each side, those in the middle of
the series having a length of 10 or sometimes 12 feet. They are black in
colour, fine and highly elastic in texture, and fray out at the inner
edge and ends into long, delicate, soft, almost silky, but very tough,
hairs. The remarkable development of the mouth and the structures in
connection with it, which distinguishes the Right Whale among all its
allies, is entirely in relation to the nature of its food. It is by this
apparatus that the animal is enabled to avail itself of the minute but
highly nutritious crustaceans and pteropods which swarm in immense shoals
in the seas it frequents. The large mouth enables it to take in at one
time a sufficient quantity of water filled with these small organisms,
and the length and delicate structure of the baleen provide an efficient
strainer or hair-sieve by which the water can be drained off. If the
baleen were rigid, and only as long as is the aperture between the upper
and lower jaws when the month is shut, a space would be left beneath it
when the jaws were separated, through which the water and the minute
particles of food would escape together. But instead of this the long,
slender, brush-like, elastic ends of the whalebone blades fold back when
the mouth is closed, the front ones passing below the hinder ones in a
channel lying between the tongue and the lower jaw. When the month is
opened, their elasticity causes them to straighten out like a bow unbent,
so that at whatever distance the jaws are separated the strainer remains
in perfect action, filling the whole of the interval. The mechanical
perfection of the arrangement is completed by the great development of
the lower lip, which rises stiffly above the jaw-bone and prevents the
long, slender, flexible ends of the baleen from being carried outwards by
the rush of water from the mouth, when its cavity is being diminished by
the closure of the jaws and raising of the tongue.
If, as appears highly probable, the “bowhead” of the Okhotsk Sea and
Behring Strait belongs to this species, its range is circumpolar. Though
found in the seas on both sides of Greenland, and passing freely from
one to the other, it is never seen so far south as Cape Farewell; but on
the Labrador coast, where a cold stream sets down from the north, its
range is somewhat farther. In the Behring Sea, according to Scammon, “it
is seldom seen south of the fifty-fifth parallel, which is about the
farthest southern extent of the winter ice, while on the Sea of Okhotsk
its southern limit is about the latitude of 54°.” As has been abundantly
shown by Eschricht and Reinhardt in the case of the Greenland seas,
“everything tends to prove,” Scammon says, “that the _Balæna mysticetus_
is truly an ‘ice whale,’ for among the scattered floes, or about the
borders of the ice-fields or barriers, is its home and feeding-ground.
It is true that these animals are pursued in the open water during
the summer months; but in no instance have we learned of their being
captured south of where winter ice-fields are occasionally met with.” The
occurrence of this species, therefore, on the British or any European
coast is exceedingly unlikely, as when alive and in health the southern
limit of its range in the North Sea has been ascertained to be from the
east coast of Greenland at 64° N. lat. along the north of Iceland towards
Spitsbergen, and a glance at a physical chart will show that there are
no currents setting southwards which could bear a disabled animal or a
floating carcase to British shores. To this _à priori_ improbability may
be added the fact that no authentic instance has been recorded of the
capture or stranding of this species upon any European coast; for the
cases in which it has been reported as seen in British waters may be
explained by the supposition of one of the other species of the genus
being mistaken for it. Still, as two other essentially Arctic Cetaceans,
the Narwhal and the Beluga, have in a few undoubted instances found
their way to British shores, it would be rash absolutely to deny the
possibility of the Greenland Right Whale doing the same.
[Illustration: FIG. 77.—Southern Right Whale (_Balæna australis_).]
The southern Right Whale (_B. australis_, Fig. 77) resembles the last
in the absence of dorsal fin and of longitudinal furrows in the skin of
the throat and chest, but differs in that it possesses a smaller head
in proportion to its body, shorter baleen, a different shaped contour
of the upper margin of the lower lip, and a greater number (fifteen) of
ribs and dorsal vertebræ. This form inhabits the temperate seas of both
northern and southern hemispheres, and is divided into several so-called
species, according to their geographical distribution:—_B. biscayensis_
of the North Atlantic, _B. japonica_ of the North Pacific, _B. australis_
of the South Atlantic, and _B. antipodarum_ and _B. novæ-zealandiæ_ of
the South Pacific. The differential characters by which they have been
separated, external as well as anatomical, are, however, slight and
subject to individual variation; and the number of specimens available
for comparison in museums is not yet sufficient to afford the necessary
data to determine whether these characters can be regarded as specific
or not. The most interesting of these is the Atlantic Right Whale, which
was formerly abundant in the North Atlantic, but is now so scarce as to
appear verging on extinction. This was the Whale the pursuit of which
gave occupation to a numerous population on the shores of the Basque
provinces of France and Spain in the Middle Ages. From the tenth to
the sixteenth centuries Bayonne, Biarritz, St. Jean de Luz, and San
Sebastian, as well as numerous other towns on the north coast of Spain,
were the centres of an active Whale “fishery,” which supplied Europe
with oil and whalebone. In later times these Whales were pursued as
far as the coast of Newfoundland. They were, however, already getting
scarce when the voyages undertaken towards the close of the sixteenth
century for the discovery of the north-eastern route to China and the
East Indies opened out the seas around Spitzbergen; then for the first
time the existence of the Greenland Whale became known, and henceforth
the energies of the European whale-fishers were concentrated upon that
animal. It is a singular fact that the existence of the Atlantic Right
Whale was quite overlooked by naturalists till lately, all accounts
referring to it being attributed to the Greenland Whale, supposed once to
have had a wider distribution than now, and to have been driven by the
persecution of man to its present circumpolar haunts. To the two Danish
cetologists Eschricht and Reinhardt is due the credit of having proved
its existence as a distinct species, from a careful collation of numerous
historical notices of its structure, distribution, and habits; and
their restoration of the animal, founded upon these documents, has been
abundantly confirmed by the capture of various specimens in recent times,
showing that it still lingers in some of the localities where it formerly
was so abundant. The only known instances of its occurrence on the coasts
of Europe in modern times are in the harbour of San Sebastian in January
1854, in the Gulf of Taranto, in the Mediterranean, in February 1877, and
on the Spanish coast between Guetaria and Zarauz (Guipuzcoa) in February
1878. The skeletons of these three whales are preserved in the museums
of Copenhagen, Naples, and San Sebastian respectively. On the coast of
the United States several Whales of this species have been taken within
the last few years. In the North Pacific a very similar if not identical
species is regularly hunted by the Japanese, who tow the carcases
ashore for the purposes of flensing and extracting the whalebone. In
the tropical seas, however, according to Captain Maury’s whale charts,
Right Whales are never or rarely seen; but the southern temperate ocean,
especially the neighbourhood of the Cape of Good Hope, Kerguelen’s
Island, Australia, and New Zealand, is inhabited by “Black Whales,” once
abundant, but now nearly exterminated through the wanton destruction of
the females as they visit the bays and inlets round the coast, their
constant habit in the breeding time. The range of these Whales southward
has not been accurately determined; but no species corresponding with the
Arctic Right Whale has as yet been met with in the Antarctic icy seas.
[Illustration: FIG. 78.—The right tympanic bone of an immature individual
of the Greenland Whale (_Balæna mysticetus_), from the inner (_A_) and
outer (_B_) aspects. ¹⁄₃ natural size. (From the _Proc. Zool. Soc._)]
Remains of Right Whales are of not uncommon occurrence in the Pliocene
Crag deposits of England and Belgium. The tympanics of _B. affinis_
from these deposits appear to indicate a species closely allied to
_B. mysticetus_, in which this bone is long and angulated anteriorly
(Fig. 78); while the tympanics from the same deposits described as _B.
primigenia_ are shorter and more rounded at the antero-inferior angle,
thus resembling those of _B. australis_. A smaller species, having an
estimated length of about 20 feet, has been described as _Balænula
balænopsis_, the generic distinction being made on account of the free
condition of the atlas and seventh cervical vertebræ; but it seems
scarcely advisable to regard such a feature as indicating more than a
less specialised species. _Balæna (Balænotus) insignis_ is a whale of
somewhat larger dimensions, in which the atlas is generally, and the
seventh cervical vertebra always, free, while in young individuals the
axis vertebra may likewise be separate.
_Neobalæna._[132]—Head about one-fourth the total length. Skin of the
throat not plicated. A small falcate dorsal fin. Vertebræ, C 7, D 17, L
3, C 16 = 43. The cervical vertebræ are united. The manus small, narrow,
and tetradactylous, wanting the pollex. The ribs remarkably expanded and
flattened. The scapula very low and broad, with completely developed
acromion and coracoid processes. Tympanic approximating to that of
_Balæna_, but with certain very characteristic peculiarities of shape.
Baleen very long, slender, elastic, and white. A single species, at
present very rare, _N. marginata_, from the Australian and New Zealand
seas is the smallest of the Whalebone Whales, being not more than 20 feet
in length.
_Rhachianectes._[133]—This combines the small head, elongated form, and
narrow pectoral fin of _Balænoptera_ with the smooth skin of the throat
and absence of the dorsal fin of _Balæna_. The baleen is the shortest and
coarsest of any of the group. Its osteology is imperfectly known. One
species, _R. glaucus_, the Gray Whale of the North Pacific.
_Megaptera._[134]—Head of moderate size. Baleen plates short and broad.
Vertebræ, C 7, D 14, L 11, C 21 = 53. Cervical vertebræ free. Scapula
with acromion and coracoid process absent or rudimentary. Skin of throat
plicated. Dorsal fin low. Pectoral limb tetradactylous, very long and
narrow, attaining about one-fourth of the length of the entire animal,
the metacarpus and phalanges being greatly developed, and the latter very
numerous. Tympanic still more inflated than in _Balænoptera_, with the
involuted portion more distinctly pyriform, the Eustachian part of the
aperture well defined, and two well-marked longitudinal ridges on the
lower surface of adult specimens.
The Whale commonly called “Humpback” (_Megaptera boops_) by whalers,
perhaps on account of the low hump-like form of the dorsal fin, is very
distinctly characterised from all others of the group, especially by the
immense length of the pectoral fins or flippers, which are indented or
scalloped along their margins, and are, except at their base, of a white
colour, nearly all the rest of the body being black. The baleen plates
are of a deep black colour. Though common in the North Atlantic between
Norway and Greenland, this Whale does not frequently appear on the coasts
of the British Isles. One came ashore at Newcastle in 1839; another, a
young one, was taken in the estuary of the Dee in 1863, and its skeleton
is preserved in the Liverpool museum; and a nearly full-grown animal
was captured in the mouth of the Tay in the winter of 1883-84.[135]
The usual length of the adult ranges from 45 to 50 feet, the female
being larger than the male. Whales of the genus _Megaptera_ are found
in the South Atlantic and in both the North and the South Pacific. They
resemble those of British seas so closely that it is doubtful whether the
differences which have been observed, and upon which several species have
been founded, may not be individual peculiarities; but zoologists have
not yet had the opportunity of examining and comparing such a series of
specimens of different ages and sexes from different localities as would
be necessary to determine these points satisfactorily.
[Illustration: FIG. 79.—Humpbacked Whale (_Megaptera boops_).]
Tympanic bones of _Megaptera_ occur in the English and Belgian Crags,
although somewhat less commonly than those of _Balæna_ and _Balænoptera_;
they have been described under the names of _Megapteropsis_ and
_Burtinopsis_.
[Illustration: FIG. 80.—The Common Rorqual (_Balænoptera musculus_).]
_Balænoptera._[136]—Head small and flat, and pointed in front. Body long
and slender. Skin of throat plicated. A small falcate dorsal fin. Baleen
short and coarse. Cervical vertebræ free. Scapula low and broad, with a
large acromion and coracoid process. Pectoral limb tetradactylous, small,
narrow, and pointed. Tympanic (Fig. 81) long, much inflated, and rounded,
with the involuted portion thickened and pyriform, and the notch for the
Eustachian canal sharply defined; inner surface flattened, without the
vertical groove found in _Megaptera_.
[Illustration: FIG. 81.—The right tympanic of _Balænoptera musculus_ from
the inner (A) and outer (B) aspects. ½ natural size. (From the _Proc.
Zool. Soc._)]
The Rorquals, Fin-Whales, Fin-backs, Finners, or Razor-backs, as they
are variously called, have the plicated skin of the throat like that
of _Megaptera_, the furrows being more numerous and close set; but the
pectoral fin is comparatively small, the dorsal fin distinct and falcate,
and the tail very much compressed before it expands into the “flukes.”
The Rorquals are perhaps the most abundant and widely distributed of
all the whales, being found in some of their modifications in all seas,
except the extreme Arctic, and probably Antarctic regions. Owing to the
small quantity and inferior quality of their whalebone, the comparatively
limited amount of blubber, and their great activity and the difficulty of
capturing them by the old methods, these Whales were not until recently
an object of pursuit by whale-fishers; but, since the introduction of
steam-vessels, and especially of explosive harpoons fired from guns in
the place of those hurled by the human hand, a regular fishery has been
established on the coast of Finmark. There are four distinct species
of this genus in British seas. (1) _Balænoptera sibbaldi_, the “Blue
Whale,” the largest of all known animals, attains a length of 80 or even
sometimes 85 feet. Its colour is dark bluish gray, with small whitish
spots on the breast; the baleen is black; the flippers are larger
proportionally than in other Rorquals, measuring one-seventh of the
total length of the body; and the dorsal fin is small and placed very
far back. This Whale has usually 64 vertebræ, of which 16 bear ribs.
Like the others of the genus, this species seems to pass the winter in
the open seas, and approaches the coast of Norway at the end of April
or beginning of May. At this time its sole food is a small crustacean
(_Euphausia inermis_) which swarms in the fjords. Several specimens have
been taken on the British coasts, two fine skeletons from the Firth
of Forth being preserved in the Edinburgh museums. (2) _Balænoptera
musculus_, the Common Rorqual, has a length of 65 to 70 feet, is of a
grayish slate colour above and white underneath, and the baleen is slate
colour variegated with yellow or brown. It has usually 62 vertebræ, of
which 15 bear ribs. This is the commonest of all the large Whales on
the British coasts, scarcely a winter passing without the body of one
being somewhere washed ashore, usually after stormy weather, and more
frequently on the south coast, as this species has a more southern range
than the last, and frequently enters the Mediterranean. It feeds largely
on fish, and is frequently seen feasting among shoals of herring. (3)
_Balænoptera borealis_, often called Rudolphi’s Whale from its first
describer, is a smaller species, scarcely attaining a length of 50 feet.
It is bluish-black above, with oblong, light-coloured spots, whilst
the under parts are more or less white; the whole of the tail and both
sides of the flippers are black; the baleen is black, and the bristly
ends fine, curling, and white; the flippers are very small, measuring
one-eleventh of the total length of the body. There are 56 vertebræ,
with 14 pairs of ribs. This species, according to Collett, feeds chiefly
on minute crustaceans, mainly _Calanus finmarchicus_ and _Euphausia
inermis_, and not on fish. Until lately it was considered the rarest of
the Whales of European seas, and was only known to science from a few
individuals stranded on the coasts of northern Europe at long intervals,
the skeletons of which have been preserved in museums. The most southern
point at which it has been met with hitherto is Biarritz in France. Since
the establishment of the whaling station near the North Cape it has been
shown to be a regular summer visitor, and in 1885, 771 individuals were
captured on the coast of Finmark. (4) _Balænoptera rostrata_, the lesser
Fin-Whale or Rorqual, is the smallest species found in the northern seas,
rarely exceeding 30 feet in length. Its colour is grayish-black above,
whilst the under side is white, including the whole of the lower side of
the tail; the inner side of the flippers is white; and there is a broad
white band across the outer side, which is a very characteristic mark of
the species; the baleen is yellowish-white. The dorsal fin in this and
the last species is comparatively high, and placed far forwards on the
body. This Whale has usually 48 vertebræ, 11 of which bear ribs. It is
common in summer in the fjords of Norway, and is often seen around the
British Isles. It has been taken, though rarely, in the Mediterranean;
and ranges as far north as Davis’s Straits.
Rorquals are met with in almost all seas throughout the world, but
further and more accurate observations are required before their
specific characters and geographical distribution can be made out. Nearly
all the individuals hitherto examined with any care, whether from the
North Pacific, the Australian seas, or the Indian Ocean, come very near
in structure to one or the other of the Atlantic forms described above,
so much so that some zoologists have been induced to believe that there
are but four species, each of which has a wide, almost cosmopolitan
range, while others have described and named almost every individual
specimen captured as belonging to a different species.[137]
Tympanics, vertebræ, and other bones of Rorquals are among the commonest
cetacean remains found in the Pliocene Crags of England and Belgium.
Several species, varying in dimensions, are known from these deposits,
_B. definita (sibbaldina)_ being apparently nearly related to the
existing _B. sibbaldi_. A caudal vertebra from the Upper Eocene of
Hampshire has been referred to _Balænoptera_, but does not afford
sufficient evidence to prove the existence of the genus at that date.
_Extinct Genera._—The extinct genus _Cetotherium_ of the European
Pliocene may be taken to include a number of fossil Whalebone Whales
allied to the Balænopterine group, several of which have been
described under other names, such as _Plesiocetus_, _Heterocetus_, and
_Amphicetus_. They are readily characterised by the form of the tympanic
bone, which is much narrower in front than behind, the roughened inferior
surface being in the shape of an isosceles triangle, and the notch for
the Eustachian canal being smaller, and descending nearer to the inferior
border of the inner wall than in _Balænoptera_. The skull is longer than
the latter, with a greater interval between the occiput and the frontal,
and with longer and more flattened nasals. The relative thickness of
the cervical vertebræ is also greater. In the typical forms (_e.g._ _C.
brialmonti_ and _C. dubium_) the mandibular condyle is simple; but in _C.
(Heterocetus) brevifrons_ it is furnished with a projecting posterior
talon, as in the Sperm Whale.
_Herpetocetus_ is known by a comparatively small species from the
Belgian and English Crags, characterised by the extreme inflation of the
egg-shaped tympanic bone, which approximates to that of _Megaptera_, but
has the greater part of the cavity filled by bone. There is a talon to
the condyle of the mandible.
_Palæocetus_, as already mentioned (p. 232), is founded upon the
ankylosed cervical vertebræ of a small Whale originally considered as
having been derived from the Kimeridge Clay, but which doubtless came
from the Suffolk Crag; if it belongs to the _Balænidæ_ it indicates a
Right Whale.
_Suborder_ ARCHÆOCETI.
_Family_ ZEUGLODONTIDÆ.
This group is formed to include certain extinct Cetacean-like animals at
present only known by more or less fragmentary portions of their skeleton
and teeth, and whose position and affinities are, therefore, still
subject to doubt.[138]
In the anterior part of both jaws the teeth are simple, conical, or
slightly compressed, and sharp pointed. The first three in the upper jaw
are distinctly implanted in the premaxillary bone, and so may be reckoned
as incisors. The tooth which succeeds, or the canine, is also simple and
conical, but it does not exceed the others in size. This is followed by
five teeth having two distinct roots and compressed pointed crowns, with
denticulated cutting-edges. The dentition is therefore _i_ ³⁄₃, _c_ ¹⁄₁,
_p_ and _m_ ⁵⁄₅ = 36, resembling that of some Seals.[139] General form
of the skull elongated and much depressed. Brain-cavity very small, and
the skull between it and the orbits elongated and narrow. Temporal fossæ
very large. A strong sagittal crest. Rostrum long and narrow, differing
from that of other Cetaceans in the large extent to which the premaxillæ
form the sides of the anterior extremity. Nasal bones elongated, flat,
and narrow, the opening of the anterior nares being over the middle of
the elongated compressed rostrum. All the cervical vertebræ free. The
characters of the dorsal vertebræ and mode of articulation of the ribs
appear to have resembled those of _Platanista_ rather than _Balæna_,
_Physeter_, or _Delphinus_. Lumbar vertebræ with elongated bodies, low
neural spines, and the transverse processes placed low down on the
bodies. Characters of the limbs not known with certainty.[140]
All the known fossil remains belonging to the animals of this group may
be referred, provisionally at least, to the genus _Zeuglodon_, so named
because the first section of a molar tooth examined was taken from the
base of the crown, where it was beginning to divide into the two roots,
and looked like two single teeth “linked or yoked together.” This name
was substituted by Owen for the earlier one _Basilosaurus_ of Harlan,
with the consent of that author, on the mammalian nature of the animal
being demonstrated.[141] The latter name is, however, still generally
retained by American zoologists. The remains have hitherto been found
chiefly in the Eocene formations of the States of Alabama, Louisiana,
Mississippi, and Arkansas, and have been assigned to several species.
A portion of a skull is recorded from the Barton Clay (Eocene) of
Hampshire, England.
_Suborder_ ODONTOCETI, _the_ DELPHINOIDEA, _or Toothed Whales_.
Calcified teeth always present after birth; generally numerous, but
sometimes a very limited number (in a few cases none) are functionally
developed. No baleen. Upper surface of the skull more or less
asymmetrical. Nasal bones in the form of nodules or flattened plates,
applied closely to the frontals, and not forming any part of the roof to
the narial passage, which is directed upwards and backwards. Olfactory
organ rudimentary or absent. Hinder end of the maxilla expanded and
covering the greater part of the orbital plate of the frontal bone.
Lachrymal bone either inseparable from the jugal, or, when distinct,
very large, and forming part of the roof of the orbit. Tympanic bone
not ankylosed with the periotic, which is usually only attached to the
rest of the skull by ligament. Rami of mandible nearly straight, much
expanded in height posteriorly, with a wide funnel-shaped aperture to
the dental canal, and coming in contact in front by a flat surface of
variable length, but always constituting a true symphysis. Several of the
anterior ribs with well-developed capitular processes, articulating with
the bodies of the vertebræ. Sternum almost always composed of several
pieces, placed one behind the other, with which several pairs of ribs
are always connected by the intervention of well-developed cartilaginous
or ossified sternal ribs. External respiratory aperture single, the two
nostrils uniting before they reach the surface, usually in the form of a
transverse subcrescentic valvular aperture, situated on the top of the
head. Manus always pentadactylous, though the first and fifth digits are
usually very little developed. No cæcum, except in _Platanista_.
_Family_ PHYSETERIDÆ.
No functional teeth in the upper jaw. Mandibular teeth various, often
much reduced in number. Bones of the cranium raised so as to form an
elevated prominence or crest behind the nares. Pterygoid bones thick,
produced backwards, meeting in the middle line, and not involuted to form
the outer wall of the post-palatine air-sinuses, but simply hollowed
on their outer side. Anterior facet of periotic bone (Fig. 87) for
articulation with the tympanic quite smooth; and the posterior tympanic
surface of the former broad, with a median longitudinal ridge. Transverse
processes of the arches of the dorsal vertebræ, to which the tubercles
of the ribs are attached, ceasing abruptly near the end of the series,
and replaced by processes on the body at a much lower level, and not on a
line or serially homologous with them, but serially homologous anteriorly
with the heads of the ribs, and posteriorly with the transverse
processes of the lumbar vertebræ. (In some genera, as _Physeter_, the
two processes, upper and lower on each side, are both present and well
developed in the same vertebra in the region of transition. In others,
as _Ziphius_ and _Berardius_, they are not both developed on any single
vertebra.) Costal cartilages not ossified.
Subfamily =Physeterinæ=.—Numerous teeth in the mandible, which are not
set in distinct bony alveoli, but in a long groove imperfectly divided by
partial septa, and held in place by the strong, fibrous gum surrounding
them. No distinct lachrymal bone. Cranium strikingly asymmetrical in
the region of the narial apertures, in consequence of the left opening
greatly exceeding the right in size.
[Illustration: FIG. 82.—Skull of Sperm Whale (_Physeter macrocephalus_).]
_Physeter._[142]—Upper teeth apparently of uncertain number, rudimentary,
and functionless, being embedded in the gum. Lower jaw with from 20 to
25 teeth on each side, stout, conical, recurved, and pointed at the
apex until they are worn, without enamel. Upper surface of the cranium
concave; its posterior and lateral edges raised into a very high and
greatly compressed semicircular crest or wall. Zygomatic processes of
jugal bones thick and massive. Rostrum greatly elongated, broad at the
base, and gradually tapering to the apex. Upper edge of the mesethmoid
forming a roughened irregular projection between the narial apertures,
inclining to the left side. Mandible exceedingly long and narrow, the
symphysis being more than half the length of the ramus. Vertebræ: C 7,
D 11, L 8, C 24; total 50. Atlas free; all the other cervical vertebræ
united by their bodies and spines into a single mass. Eleventh pair of
ribs rudimentary. Head about one-third the length of the body; very
massive, high and truncated, and rather compressed in front; owing its
huge size and remarkable form mainly to the accumulation of an oily
substance secreted by the lining membranes of great cells surrounding the
narial passage and filling the large hollow on the upper surface of the
cranium and overlying the rostrum. The single blowhole is longitudinal,
slightly sigmoid, and placed at the upper and anterior extremity of the
head to the left side of the middle line. The opening of the mouth is on
the under side of the head, considerably behind the end of the snout.
Pectoral fin short, broad, and obliquely truncated. Dorsal fin a mere low
protuberance.
[Illustration: FIG. 83.—The Sperm Whale (_Physeter macrocephalus_).]
The only representative of this genus is the Cachalot or Sperm Whale (_P.
macrocephalus_, Fig. 83), one of the most colossal of animals, quite
equalling, if not exceeding, the Greenland Whale in bulk. The length of
the full-grown male is from 55 to 60 feet, but the female is stated not
to reach more than half that size. The general colour of the surface
is black above and gray below, the colours gradually shading into each
other. The Sperm Whale is one of the most widely distributed of animals,
being met with usually in herds or “schools” in almost all tropical and
subtropical seas, but not occurring, except accidentally, in the Polar
regions. Not unfrequently specimens appear on the coasts of the British
Isles, but only as solitary stragglers, or as dead carcases, floated
northwards by the Gulf Stream. It is remarkable that every one of these
of which we have an accurate record has been an old male. The food of
this Whale consists mainly of various species of cephalopods (squid and
cuttle-fish), but fish of considerable size are also eaten. The substance
called “ambergris,” formerly used in medicine and now in perfumery, is a
concretion formed in the intestine of this Whale, and is found floating
on the surface of the seas it inhabits. Its genuineness is proved by the
presence of the horny beaks of the cephalopods on which the Whale feeds.
The oil contained in the great cavity above the skull, when refined,
yields “spermaceti,” and the thick covering of blubber which everywhere
envelops the body produces the valuable “sperm-oil” of commerce; hence
this animal has long been the subject of a regular chase, by which its
numbers have been greatly diminished.
_Cogia._[143]—Teeth of the upper jaw absent, or reduced to a rudimentary
pair in front; in the lower jaw 9 to 12 on each side, rather long,
slender, pointed, and curved, with a coating of enamel. Upper surface
of the cranium concave, with thick, raised posterior and lateral
margins, massive and rounded at their anterior terminations above the
orbits. Upper edge of the mesethmoid forming a prominent sinuous ridge,
constituting a kind of longitudinal septum to the base of the great
supra-cranial cavity. Rostrum not longer than the cranial portion of the
skull, broad at the base, and rapidly tapering to the apex. Zygomatic
process of the jugal styliform. Mandible with the symphysis less than
half the length of the entire ramus. Vertebræ: C 7, D 13 or 14, L and C
30; total 50 or 51. All the cervical vertebræ united by their bodies and
arches. External characters not well known, but, judging by the somewhat
conflicting accounts of those that have had an opportunity of observing
them, the head is about one-sixth of the length of the body, and obtusely
pointed in front; the mouth small, and placed far below the apex of the
snout; the spiracle crescentic, and placed obliquely on the top of the
head anteriorly to the eyes, and to the left of the middle line; the
pectoral fins are obtusely falcate; and there is a triangular dorsal fin.
The history of this genus is a good illustration of the difficulties
in which the study of the Cetacea has been involved by the superficial
manner in which it has been investigated. The first known example, a
skull from the Cape of Good Hope in the Paris Museum, was described by De
Blainville under the name of _Physeter breviceps_. This was afterwards
with good reason generically separated by Gray. Until within a very
few years ago only five other individuals had been met with, each of
which had been described under a different specific name (viz. _grayi_,
_macleayi_, _simus_, _floweri_, and _potsii_), and which are arranged
by Gray in two distinct genera. The most careful examination of the
description given of these specimens, or of the now numerous osteological
remains available, fails to detect any differences beyond those which
may be attributed to age or sex, and hence, according to our present
knowledge, these six supposed species must all be included under one
name, _C. breviceps_. This animal appears to attain the length of 10 feet
when adult, and has been met with at various distant localities in the
Southern Ocean, and also off the coast of Madras and in the North Pacific.
_Extinct Physeteroids._—Teeth of Physeteroids are of very common
occurrence in the Belgian and English Crags, and evidently indicate the
former existence of Whales more or less closely allied to the Sperm
Whale, but often distinguished by the presence of an enamel-cap on
the crowns of the teeth. The generic determination of these teeth is,
however, exceedingly difficult, owing to the water-worn condition in
which they are frequently found, and also on account of the impossibility
of knowing whether small and large teeth may not be referable to
different parts of the jaws of the same species or to individuals of
different ages. Moreover, in the cases of isolated teeth it is impossible
to know how many were contained in the jaws, and therefore to distinguish
Physeteroid from Ziphioid teeth. _Physeterula_ is a small form about
one-third the dimensions of the Sperm Whale, and distinguished by the
length of the mandibular symphysis being only about one-third that of the
entire ramus; it is identified by Professor Cope with _Cogia_. _Eucetus_
(_Dinoziphius_) is founded on teeth which are regarded as closely
resembling those of _Physeter_, but distinguished by their subcylindrical
form and the small size of the aperture of the pulp-cavity. It does not
appear, however, to be certain that these teeth are not worn specimens
of those described as _Scaldicetus_. _Physetodon_, from the Pliocene of
Australia, is founded upon the evidence of similar teeth. The teeth from
the Belgian Crag described as _Scaldicetus_ are somewhat smaller than
those of the Sperm Whale, and are readily characterised by their cap
of grooved enamel. Other teeth with enamel-caps have been described as
_Physodon_ and _Hoplocetus_. The genus _Balænodon_ is founded upon a very
imperfect large tooth from the English Crag, which is not sufficiently
well preserved to admit of exact comparison with the other types.
Subfamily =Ziphiinæ=.—Teeth of the mandible (at least in existing forms)
quite rudimentary and concealed in the gum, except one, or very rarely
two, pairs which may be largely developed, especially in the male sex.
A distinct lachrymal bone. Externally the mouth is produced into a
slender rostrum or beak, from above which the rounded eminence formed by
a cushion of fat resting on the cranium in front of the blowhole rises
somewhat abruptly. Spiracle or blowhole single, crescentic, median, as
in the _Delphinidæ_. Pectoral fin small, ovate, the five digits all
moderately well developed. A small obtusely falcate dorsal fin situated
considerably behind the middle of the back. Longitudinal grooves on
each side of the skin of the throat, diverging posteriorly, and nearly
meeting in front. In external characters and habits the animals of this
group closely resemble each other. They appear to be almost exclusively
feeders on various species of cephalopods, and occur either singly, in
pairs, or in small herds. By their dental and osteological characters
they are easily separated into four distinct genera.
_Hyperoödon._[144]—A small conical pointed tooth at the apex of each
ramus of the mandible, concealed by the gum during life. Skull with the
upper ends of the premaxillæ rising suddenly behind the nares to the
vertex and expanded laterally, their outer edges curving backwards and
their anterior surfaces arching forwards and overhanging the nares; the
right larger than the left. Nasal bones lying in the hollow between the
upper extremities of the premaxillæ, strongly concave in the middle line
and in front; their outer edges, especially on the right side, expanded
over the front of the inner border of the maxilla. Very high longitudinal
crests on the maxillæ at the base of the rostrum, extending backwards
almost to the nares, approaching each other in the middle line above;
sometimes so massive that their inner edges come almost in contact.
Anteorbital notch distinct. Mesethmoid but slightly ossified. Vertebræ:
C 7, D 9, L 10, C 19; total 45. All the cervical vertebræ united. Upper
surface of the head in front of the blowhole hole very prominent and
rounded, rising abruptly from above the small, distinct snout.
[Illustration: FIG. 84.—_Hyperoödon rostratus._ From a female specimen
taken off the coast of Scotland, 1882.]
The genus is known typically by _H. rostratus_ (Fig. 84), but an
imperfect skull has been made the type of _H. planifrons_—a species
differing considerably in cranial characters from the typical one. The
females and young males of the first-named species have the contour of
the head of the same general form as in Fig. 84; the premaxillary crests
of the cranium being widely separated from one another, and terminating
in comparatively sharp edges. In the males, however, as age advances the
summits of these crests become gradually expanded and flattened, till
they are almost or quite in contact in the middle line. This development
of the maxillary crests produces a corresponding elevation and flattening
of the front of the head, so that in very old males this aspect presents
a flattened disc-like surface rising abruptly from the beak (which thus
becomes almost buried) and situated in a plane nearly at right angles to
the line of the back.[145] So different, indeed, is the appearance of the
skull of an old male from that of a female individual that it was long
considered that they belonged to different species—the male form having
been described as _H. latifrons_. The length of an adult male reaches 30
feet, while that of the female does not exceed 24 feet.
The Hyperoödon, sometimes called “Bottlenose,” a name also vaguely given
to several species of Dolphin, is a regular inhabitant of the North
Atlantic, passing the summer in the Spitzbergen seas and going farther
south in winter. It resembles the Sperm Whale in possessing a large
store of oil in the upper part of the head, which yields spermaceti when
refined; on this account, and also for the sake of the blubber, which
supplies an oil almost indistinguishable from sperm-oil, this Whale has
been the object of a regular chase in recent years.
The following account of its habits is taken from a paper by Captain D.
Gray, published in the _Zoological Society’s Proceedings_ for 1882:—
“These Whales are occasionally met with immediately after leaving the
Shetland Isles in March, and north across the ocean until the ice is
reached, near the margin of which they are found in the greatest numbers;
but they are seldom seen amongst it. Although it is not in their nature
to keep in amongst the ice, they like to frequent the open bays for the
shelter it gives them from the sea. Sometimes a point of ice overlaps
them; it is then only that they are seen going out again towards the
ocean. They are also to be met with from the entrance of Hudson’s Straits
and up Davis’s Straits, as far as 70° N. lat., and down the east side
round Cape Farewell, all round Iceland, north along the Greenland ice
to 77° N. lat.; also along the west coast of Spitzbergen, and east to
Cherry Island in lat. 72° N. and long. 19° E. Beyond these limits I
have never seen them; but doubtless they are to be found as far as the
Straits of Belle Isle on the west, and east to Nova Zembla. From the
fact that they are not seen in summer farther south than a day’s sail
from the ice, it would appear that they migrate south in the autumn, and
north again in the spring. They are gregarious in their habits, going
in herds of from four to ten. It is rare to see more than the latter
number together, although many different herds are frequently in sight
at the same time. The adult males very often go by themselves; but young
bulls, cows, and calves, with an old male as a leader, are sometimes seen
together. They are very unsuspicious, coming close alongside the ship,
round about underneath the boats, until their curiosity is satisfied....
They vary in colour from black in the young to light brown in the
older animals. The very old turn almost yellow, the beak and front of
the head being quite white, with a white band round their necks; all
of them are grayish-white on the belly. They can leap many feet out
of the water, even having time while in the air to turn round their
heads and look about them, taking the water head first, and not falling
helplessly into it sideways like the larger whales. The full-grown
whale is 30 feet long by 20 feet in circumference, and yields two tons
of oil besides two hundredweight of spermaceti.... Their ordinary food
consists of a bluish-white cuttle-fish, six inches long by three inches
in circumference, and pointed towards the tail.... They evidently have a
great depth to go to find them, judging from the length of time that they
remain away, and from the long heavy blasts they make on coming to the
surface again.”
Periotic bones of _Hyperoödon_ are found in the Red Crag of Suffolk,
presenting no character by which they can be specifically distinguished
from those of the common existing species.
_Ziphius._[146]—A single conical tooth of moderate size on each side of
the mandible close to the anterior extremity, and directed forwards and
upwards. Skull with the premaxillæ immediately in front of, and at the
sides of the nares expanded, hollowed, and with elevated lateral margins,
the posterior ends rising to the vertex and curving forwards, the right
being considerably more developed than the left; the conjoint nasals
forming a strongly pronounced symmetrical eminence at the top of the
cranium, projecting forwards over the nares, flat above, most prominent
and rounded in the middle line in front, and separated by a notch on
each side from the premaxillæ. Anteorbital notch not distinct. Rostrum
(seen from above) triangular, gradually tapering from the base to the
apex; upper and outer edges of maxillæ at base of rostrum raised into low
roughened tuberosities. Mesethmoid cartilage densely ossified in adult
age, and coalescing with the surrounding bones of the rostrum. Vertebræ:
C 7, D 10, L 10, C 22; total 49. The three anterior cervical vertebræ
united, the rest free.
The type of this genus is _Z. cavirostris_ of Cuvier, founded upon an
imperfect skull picked up in 1804 on the Mediterranean coast of France,
and described and figured in the _Ossemens Fossiles_ under the impression
that it was that of an extinct species. Many other individuals have,
however, been subsequently met with in various parts of the world, from
the Shetland Islands to New Zealand, all referable to the same genus,
if not to the same species; although, as is usual in such cases, they
have mostly been described under different names, the so-called genera
_Petrorhynchus_ and _Epiodon_ being probably referable to the type
species.
It is quite probable that some of the Physeteroid teeth from the Crag
deposits mentioned on p. 251 may be referable to _Ziphius_.
[Illustration: FIG. 85.—_Mesoplodon bidens._ From Reinhardt.]
_Mesoplodon._[147]—A much compressed and pointed tooth in each ramus of
the mandible, variously situated, but generally at some distance behind
the apex (Fig. 86); its point directed upwards, and often somewhat
backwards, occasionally developed to a great size. Skull with the region
around the nares as in _Hyperoödon_, except that the nasals are narrow
and more sunk between the upper ends of the premaxillæ; like those of
_Hyperoödon_, they are concave in the middle line in front and above.
No maxillary tuberosities. Anteorbital notch not very distinct. Rostrum
long, narrow, and solid throughout. Mesethmoid in adult age ossified in
its entire length, coalescing with the surrounding bones, and showing as
a narrow band on the upper surface of the rostrum. Vertebræ: C 7, D 10,
L 10 or 11, C 19 or 20; total 46 to 48. Two or three anterior cervicals
united, the rest usually free.
[Illustration: FIG. 86.—Left lateral view of skull of _Mesoplodon
densirostris_.]
Though varying in form, the mandibular teeth of the different members
of this genus agree in their essential structure, having a small and
pointed enamel-covered crown, composed of true dentine, which, instead
of surmounting a root of the ordinary character, is raised upon a solid
mass of osteodentine. The continuous growth of this greatly alters the
form and general appearance of the organ as age advances, as seen most
strikingly in the case of _M. layardi_, where the long, narrow, flat,
strap-like teeth, curving inwards at their extremities, actually meet
over the rostrum, and must greatly interfere with the movements of the
jaw. In one species (_M. grayi_) a row of minute, conical, pointed
teeth, like those of ordinary Dolphins, 17 to 19 in number, are present
even in the adults, on each side of the middle part of the upper jaw, but
embedded by their roots only in the gum, and not in bony alveoli. This
fact, with the frequent presence of rudimentary teeth in other species of
this and the last genus in both upper and lower jaws, suggests the idea
that the Ziphioids are derived from ancestral forms which had teeth of
normal character in both jaws; the dentition of the living forms having
become greatly specialised. The existing species of this genus are widely
distributed in both northern and southern hemispheres, but most frequent
in the latter. The best established are _M. bidens_, _M. europæus_, _M.
densirostris_, _M. layardi_, _M. grayi_, and _M. hectori_; but there is
still much to be learned with regard to their distinctive characters and
geographical distribution. They were abundant in the Pliocene age, as
attested by the frequency with which the most imperishable and easily
recognised portion of their structure, the long, cylindrical rostrum
of the skull, of more than ivory denseness, is found among the rolled
and water-worn fragments of animal remains which compose the well-known
“bone-bed” at the base of the Red Crag of Suffolk Several species have
been founded upon the evidence of these rostra. Periotic bones of this
genus (Fig. 87) are of less common occurrence in the Crag; the figure
is given to illustrate the characteristic features of this bone in the
present family.
[Illustration: FIG. 87.—The left periotic bone of _Mesoplodon_; from the
Red Crag of Suffolk. The smooth concave surface in the right upper corner
of the figure forms the anterior articulation with the tympanic. (From
the _Cat. Foss. Mamm. Brit. Mus._ pt. v. p. 70.)]
_Berardius._[148]—Two moderate-sized, compressed, pointed teeth on
each side of the symphysis of the mandible, with their apices directed
forwards, the anterior being the larger of the two and close to the apex.
Upper ends of the premaxillæ nearly symmetrical, moderately elevated,
very slightly expanded, and not curved forward over the nares. Nasals
broad, massive, and rounded, of nearly equal size, forming the vertex
of the skull, flattened in front, most prominent in the middle line.
Anteorbital notch distinct. Rostrum long and narrow. Mesethmoid only
partially ossified. Small rugous eminences on the outer edge of the upper
surface of the maxillæ at base of rostrum. Vertebræ: C 7, D 10, L 12, C
19; total 48. The three anterior cervicals ankylosed, the rest free and
well developed.
The only known species, _B. arnuxi_, attains the length of 30 feet, and
has hitherto only been met with in the seas around New Zealand.
_Choneziphius._[149]—The rostral portions of crania from the Antwerp and
Suffolk Crags, on the evidence of which this genus has been established,
agree with those of _Mesoplodon_ in having the premaxillæ in contact with
the intervening bones throughout the length of their inner surfaces, and
also in showing only a very small portion of the vomer on the inferior
surface; they differ, however, in that the mesethmoid cartilage remains
unossified, whereby a fistular vacuity remains. In some species the
soldering of the inner surfaces of the premaxillæ is incomplete. The
interorbital region of the skull is flat; and there are two pits in the
nasal region, of which the right is the larger.
_Family_ SQUALODONTIDÆ.
Numerous extinct forms, chiefly known by teeth and fragments of crania,
may be provisionally placed here, until more of their osteological
characters shall be brought to light. They differ from all existing
Cetaceans in having the teeth distinctly differentiated into groups,
as in the Archæoceti, the posterior molars being two-rooted. The
cranium has, however, none of the distinguishing characteristics of the
Zeuglodonts, but essentially resembles that of the Odontoceti, especially
in the position of the anterior nares and form of the nasal bones.
_Squalodon._[150]—All the forms may be included in this genus, the
so-called _Rhizoprion_ not being distinct. Dentition: _i_ ³⁄₃, _c_ ¹⁄₁,
simple teeth of the molar series (premolars?) ⁴⁄₄, two-rooted molars
⁷⁄₇ = ¹⁵⁄₁₅; total 60. The double-rooted molars differ from those of
_Zeuglodon_ in having the denticulations of the crown confined to the
posterior border, or at all events much less developed on the front
edge. Very little is known of the structure of these animals beyond the
skull and teeth, fragments of which have been found widely distributed
throughout the marine Miocene and early Pliocene formations of Europe,
especially in the Vienna basin, many parts of France, and the Antwerp and
Suffolk Crags. They have also been found in formations of corresponding
age in North America and South Australia. A few isolated teeth have been
met with in the cave-deposits of Italy, which, if contemporaneous with
the beds in which they occur, indicate the survival of the genus into the
Pleistocene period.
_Family_ PLATANISTIDÆ.
Under this heading may be placed three very singular genera, which,
though differing considerably from each other, have several points in
common, and do not altogether come under the definition either of the
_Physeteridæ_ or the _Delphinidæ_, especially in the important character
of the mode of articulation of the ribs with the dorsal vertebræ, the
tubercular and capitular articulations, distinct at the commencement of
the series, gradually blending together, as they do in most ordinary
mammals. The cervical vertebræ are all free. The lachrymal bone is not
distinct from the jugal. The jaws are long and narrow, with numerous
teeth in both. The symphysis of the mandible exceeds half the length
of the whole ramus. Externally the head is divided from the body by a
slightly constricted neck. Pectoral limbs broad and truncated. Dorsal fin
small or obsolete. Fluviatile or estuarine in habits. There are three
distinct genera, which might almost be made the types of families, but it
is probably more convenient to keep them together, only regarding them as
representing three subfamilies.
_Platanista._[151]—Teeth about ³⁰⁄₃₀ on each side, set near together,
rather large, cylindrical, and sharp-pointed in the young; in old animals
acquiring a large laterally compressed base, which in the posterior part
of the series becomes irregularly divided into roots. As the conical
enamel-covered crown wears away, the teeth of the young and old animals
have a totally different appearance. The rostrum and dentigerous portion
of the mandible are so narrow that the teeth of the two sides are almost
in contact. Maxillæ supporting very large, incurved, compressed bony
crests, which overarch the nares and base of the rostrum, and almost meet
in the middle line above. Orbits very small and eyes rudimentary, without
crystalline lens. External respiratory aperture longitudinal, linear.
Vertebræ: C 7, D 10, L 9, C 26; total: 52. A small cæcum. No pelvic
bones. Dorsal fin represented by a low ridge.
[Illustration: FIG. 88.—_Platanista gangetica._ (From Anderson.)]
One species, _P. gangetica_, entirely fluviatile, being extensively
distributed throughout nearly the whole of the river systems, not only of
the Ganges, but of the Brahmaputra and Indus, ascending as high as there
is water enough to swim in, but never passing out to sea. It is quite
blind, and feeds on small fish and crustaceans, groping for them with
its long snout in the muddy water at the bottom of the rivers. It attains
the length of 8 feet.[152]
_Inia._[153]—Teeth variable, from 26 to 33 on either side of each jaw;
those at the posterior part with a distinct tubercle at the inner side
of the base of the crown. Vertebræ: C 7, D 13, L 3, C 18; total 41.
Transverse processes of lumbar vertebræ very broad. Sternum short and
broad, and consisting of a single segment only. Dorsal fin a mere ridge.
The long cylindrical rostrum externally furnished with scattered, stout,
and crisp hairs. One species only is known, _I. geoffroyensis_, about 7
feet in length, inhabiting the upper Amazon and its tributary streams.
_Pontoporia._[154]—Teeth 50 to 60 on either side of each jaw, with a
cingulum at the base of the crown. Jaws very long and slender. Vertebræ:
C 7, D 10, L 5, C 19; total 41. Transverse processes of the lumbar
vertebræ extremely broad. Sternum elongated, composed of two segments,
with four sternal ribs attached. Dorsal fin rather small, triangular,
pointed. External respiratory aperture transverse, crescentic. This genus
connects the last two forms with the true _Delphinidæ_. The only species,
_P. blainvillei_, is one of the smallest members of the whole order, not
exceeding 5 feet in length. It has only been met with at the mouth of the
Rio de la Plata, near Buenos Ayres, and there is at present no evidence
that it ascends into the fresh waters of the river.
[Illustration: FIG. 89.—_Pontoporia blainvillei._ (From Burmeister.)]
_Fossil forms._—Remains of a Cetacean from the Pleistocene of South
America were referred by Bravard to _Pontoporia_, but they have been
regarded by other writers as indicating a distinct genus, for which
the names _Palæopontoporia_ and _Pontistes_ have been proposed. The
Upper Tertiary European genera _Champsodelphis_ and _Schizodelphis_
are generally referred to the present family. The former has wide
transverse processes to the lumbar vertebræ, as in _Inia_, while the
teeth also resemble those of that genus. In _Schizodelphis_ the form
of the rostrum presents a great resemblance to that of the Delphinoid
genus _Steno_, but the symphysis of the mandible is relatively longer. A
number of fossil Cetaceans from the Miocene of the United States, such
as _Priscodelphinus_, _Lophocetus_, _Ixacanthus_, _Rhabdosteus_, etc.,
are referred by Professor E. D. Cope to this family. _Agabelus_, from the
same deposits, is an apparently allied, but toothless type.
_Family_ DELPHINIDÆ.
Teeth usually numerous in both jaws. Pterygoid bones short, thin, each
involuted to form with a process of the palate bone the outer wall of
the post-palatine air-sinus. Symphysis of mandible short, or moderate,
never exceeding one-third of the length of the ramus. Lachrymal bone not
distinct from the jugal. The anterior facet on the periotic (Fig. 96)
for articulation with the tympanic deeply grooved; and the posterior
tympanic surface of the same bone comparatively narrow, with its ridge
for articulation with the free border of the tympanic ill-defined, and
situated close to one edge. Transverse processes of the dorsal vertebræ
gradually transferred from the arches to the bodies of the vertebræ
without any sudden break, and becoming posteriorly continuous serially
with the transverse processes of the lumbar vertebræ. Anterior ribs
attached to the transverse process by the tubercle, and to the body of
the vertebra by the head; the latter attachment lost in the posterior
ribs. Sternal ribs firmly ossified. External respiratory aperture
transverse, crescentic, with the horns of the crescent pointing forwards.
A very large group, closely united in essential characters but
presenting great modifications in details. The different types are
mostly so connected by intermediate or osculant forms that there are
great difficulties in grouping them into natural subfamilies. Even the
formation of well-defined genera is by no means satisfactory in all
cases. They may, however, be divided, perhaps artificially, into two
groups.
_Group A._—Head rounded, without distinct rostrum or beak. Rostrum of
skull about as long as cranial portion.
_Monodon._[155]—Besides some irregular rudimentary teeth, the entire
dentition is reduced to a single pair of teeth which lie horizontally in
the maxilla, and in the female remain permanently concealed within the
alveolus so that this sex is practically toothless, while in the male
(see Fig. 90) the right tooth usually remains similarly concealed and
abortive, and the left is immensely developed, attaining a length equal
to more than half that of the entire animal, projecting horizontally from
the head in the form of a cylindrical, or slightly tapering, pointed
tusk, without enamel, and with the surface marked by spiral grooves
and ridges, running in a sinistral direction. (When, as occasionally
happens, both tusks are developed, the spiral grooves have the same
direction in each.) Pterygoids very small, not meeting in the middle
line, but approximating posteriorly. Vertebræ: C 7, D 11, L 6, C 26;
total 50. Cervical region comparatively long, and all the vertebræ
distinct, or with irregular unions towards the middle of the series, the
atlas and axis being usually free. Manus small, short, and broad; second
and third digits nearly equal, fourth slightly shorter. No dorsal fin.
This genus is now represented only by the well-known Narwhal (_M.
monoceros_), in which the horn-like tusk of the male often grows to a
length of 7 or 8 feet. In very young animals several small additional
teeth, irregular in number and position, are present, but these usually
disappear soon after birth.
The head is rather short and rounded; the fore limbs or paddles are small
and broad compared with those of most Dolphins; and (as in the Beluga)
the median dorsal fin, found in nearly all other members of the group, is
wanting or replaced by a low ridge. The general colour of the surface is
dark gray above and white below, but variously marbled and spotted with
different shades of gray. In the general contour of the body the Narwhal
resembles the White Whale or Beluga.
[Illustration: FIG. 90.—Upper surface of the skull of male Narwhal
(_Monodon monoceros_), with the whole of both teeth exposed by removal of
the upper wall of their alveolar cavities.]
The Narwhal is essentially an Arctic animal, frequenting the icy
circumpolar seas, and but rarely seen south of 65° N. lat. Three
instances have, however, been recorded of its occurrence on the
British coasts, one in the Firth of Forth in 1648, one near Boston in
Lincolnshire in 1800, while a third, which entangled itself among the
rocks in the Sound of Weesdale, Shetland, in September 1808, is described
by Fleming in the _Memoirs of the Wernerian Society_, vol. i. Like most
other Cetaceans, it is gregarious in its habits, being usually met with
in “schools” or herds of fifteen or twenty individuals. Its food appears
to be various species of cephalopods, small fishes, and crustaceans.
The purpose served in the animal’s economy by the wonderfully developed
asymmetrical tusk—or “horn,” as it is commonly but erroneously called—is
not known. As it is present only in the male sex, no function essential
to the well-being of the individual, such as the procuring of sustenance,
can be assigned to it, but it must be looked upon as belonging to the
same category of organs as the antlers of deer, and perhaps may be
applied to similar purposes. Very little is, however, known of the habits
of Narwhals. Scoresby describes them as “extremely playful, frequently
elevating their horns and crossing them with each other as in fencing.”
They have never been known to charge and pierce the bottom of ships with
their weapons, as the sword-fish often does. The name “Sea Unicorn,”
sometimes applied to the Narwhal, refers to the resemblance of its tusk
to the horn represented as projecting from the forehead of the fabled
unicorn. The ivory of which the tusk is composed is of very good quality,
but, owing to the central cavity, which extends the greater part of its
length, is only fitted for the manufacture of objects of small size.
The entire tusks are sometimes used for decorative purposes, and are of
considerable, though very fluctuating, commercial value.