SUBCLASS DIPNEUSTI,[164] OR LUNGFISHES
=The Lungfishes.=--The group of Dipneusti, or lung-fishes, is
characterized by the presence of paired fins consisting of a jointed
axis with or without rays. The skull is autostylic, the upper jaw being
made as in the Chimæra of palatal elements joined to the quadrate and
fused with the cranium, without premaxillary or maxillary. The dentary
bones are little developed. The air-bladder is cellular, used as a lung
in all the living species, its duct attached to the ventral side of the
oesophagus. The heart has many valves in the muscular arterial bulb.
The intestine has a spiral valve. The teeth are usually of large plates
of dentine covered with enamel, and are present on the pterygo-palatine
and splenial bones. The nostrils are concealed, when the mouth is
closed, under a fold of the upper lip. The scales are cycloid, mostly
not enameled.
[Illustration: FIG. 381.--Shoulder-girdle of _Neoceratodus forsteri_
Günther. (After Zittel.)]
The lung-fishes, or _Dipneusti_ (~dis~, two; ~pnein~, to breathe),
arise, with the Crossopterygians, from the vast darkness of Palæozoic
time, their origin with that or through that of the latter to be traced
to the Ichthyotomi or other primitive sharks. These two groups are
separated from all the more primitive fish-like vertebrates by the
presence of lungs. In its origin the lung or air-bladder arises as a
diverticulum from the alimentary canal, used by the earliest fishes
as a breathing-sac, the respiratory functions lost in the progress of
further divergence. Nothing of the nature of lung or air-bladder is
found in lancelet, lamprey, or shark. In none of the remaining groups
of fishes is it wholly wanting at all stages of development, although
often lost in the adult. Among fishes it is most completely functional
in the _Dipneusti_, and it passes through all stages of degeneration
and atrophy in the more specialized bony fishes.
In the _Dipneusti_, or Dipnoans, as in the Crossopterygians and the
higher vertebrates, the trachea, or air-duct, arises, as above stated,
from the ventral side of the oesophagus. In the more specialized
fishes, yet to be considered, it is transferred to the dorsal side,
thus avoiding a turn in passing around the oesophagus itself. From
the sharks these forms are further distinguished by the presence of
membrane-bones about the head. From the _Actinopteri_ (Ganoids and
Teleosts) Dipnoans and Crossopterygians are again distinguished by
the presence of the fringe-fin, or archipterygium, as the form of
the paired limbs. From the Crossopterygians the Dipnoans are most
readily distinguished by the absence of maxillary and premaxillary,
the characteristic structures of the jaw of the true fish. The upper
jaw in the Dipnoan is formed of palatal elements attached directly to
the skull, and the lower jaw contains no true dentary bones. The skull
in the Dipnoans, as in the _Chimæra_, is autostylic, the mandible
articulating directly with the palatal apparatus, the front of which
forms the upper jaw and of which the pterygoid, hyomandibular and
quadrate elements form an immovable part. The shoulder-girdle, as in
the shark, is a single cartilage, but it supports a pair of superficial
membrane-bones.
In all the Dipnoans the trunk is covered with imbricated cycloid
scales and no bony plates, although sometimes the scales are firm and
enameled. The head has a roof of well-developed bony plates made of
ossified skin and not corresponding with the membrane-bones of higher
fishes. The fish-like membrane-bones, opercles, branchiostegals, etc.,
are not yet differentiated. The teeth have the form of grinding-plates
on the pterygoid areas of the palate, being distinctly shark-like
in structure. The paired fins are developed as archipterygia, often
without rays, and the pelvic arch consists of a single cartilage,
the two sides symmetrical and connected in front. There is but one
external gill-opening leading to the gill-arches, which, as in ordinary
fishes, are fringe-like, attached at one end. In the young, as with
the embryo shark, there is a bushy external gill, which looks not
unlike the archipterygium pectoral fin itself, although its rays are of
different texture. In early forms, as in the Ganoids, the scales were
bony and enameled, but in some recent forms deep sunken in the skin.
The claspers have disappeared, the nostrils, as in the frog, open into
the pharynx, the heart is three-chambered, the arterial bulb with many
valves, and the cellular structure of the skin and of other tissues is
essentially as in the Amphibian.
The developed lung, fitted for breathing air, which seems the most
important of all these characters, can, of course, be traced only in
the recent forms, although its existence in all others can be safely
predicated. Besides the development of the lung we may notice the
gradual forward movement of the shoulder-girdle, which in most of the
Teleostomous fishes is attached to the head. In bony fishes generally
there is no distinct neck, as the post-temporal, the highest bone of
the shoulder-girdle, is articulated directly with the skull. In some
specialized forms (_Balistes_, _Tetraodon_) it is even immovably fused
with it. In a few groups (_Apodes_, _Opisthomi_, _Heteromi_, etc.)
this connection ancestrally possessed is lost through atrophy and the
slipping backward of the shoulder-girdle leaves again a distinct neck.
In the Amphibians and all higher vertebrates the shoulder-girdle is
distinct from the skull, and the possession of a flexible neck is an
important feature of their structure. In all these higher forms the
posterior limbs remain abdominal, as in the sharks and the primitive
and soft-rayed fishes generally. In these the pelvis or pelvic elements
are attached toward the middle of the body, giving a distinct back as
well as neck. In the spiny-rayed fishes the "back" as well as the neck
disappears, the pelvic elements being attached to the shoulder-girdle,
and in a few extreme forms (as _Ophidion_) the pelvis is fastened at
the chin.
=Classification of Dipnoans.=--By Woodward the _Dipneusti_ are divided
into two classes, the _Sirenoidei_ and the _Arthrodira_. We follow Dean
in regarding the latter as representative of a distinct class, leaving
the _Sirenoidei_, with the _Ctenodipterini_, to constitute the subclass
of _Dipneusti_. The _Sirenoidei_ are divided by Gill into two orders,
the _Monopneumona_, with one lung, and the _Diplopneumona_, with the
lung divided. To the latter order the _Lepidosirenidæ_ belong. To the
former the _Ceratodontidæ_, and presumably the extinct families also
belong, although nothing is known of their lung structures. Zittel
and Hay adopt the names of _Ctenodipterini_ and _Sirenoidei_ for
these orders, the former being further characterized by the very fine
fin-rays, more numerous than their supports.
=Order Ctenodipterini.=--In this order the cranial roof-bones are small
and numerous, and the rays of the median fins are very slender, much
more numerous than their supports, which are inserted directly on the
vertebral arches.
In the _Uronemidæ_ the upper dentition comprises a cluster of small,
blunt, conical denticles on the palatine bones; the lower dentition
consists of similar denticles on the splenial bone. The vertical fins
are continuous and the tail diphycercal. There is a jugular plate, as
in _Amia_. The few species are found in the Carboniferous, _Uronemus
lobatus_ being the best-known species.
In _Dipteridæ_ there is a pair of dental plates on the palatines, and
an opposing pair on the splenials below. Jugular plates are present,
and the tail is usually distinctly heterocercal.
In _Phaneropleuron_ there is a distinct anal fin shorter than the very
long dorsal; _Phaneropleuron andersoni_ is known from Scotland, and
_Scaumenacia curta_ is found at Scaumenac Bay in the Upper Devonian of
Canada.
In _Dipterus_ there are no marginal teeth, and the tail is
heterocercal, not diphycercal, as in the other Dipnoans generally.
Numerous species of _Dipterus_ occur in Devonian rocks. In these the
jugular plate is present, as in _Uronemus_. _Dipterus valenciennesi_ is
the best-known European species. _Dipterus nelsoni_ and numerous other
species are found in the Chemung and other groups of Devonian rocks in
America.
[Illustration: FIG. 382.--_Phaneropleuron andersoni_ Huxley; restored;
Devonian. (After Dean.)]
In the _Ctenodontidæ_ the tail is diphycercal, and no jugular plates
are present in the known specimens. In _Ctenodus_ and _Sagenodus_
there is no jugular plate and there are no marginal teeth. The
numerous species of _Ctenodus_ and _Sagenodus_ belong chiefly to
the Carboniferous age. _Ctenodus wagneri_ is found in the Cleveland
shale of the Ohio Devonian. _Sagenodus occidentalis_, one of the many
American species, belongs to the coal-measures of Illinois.
As regards the succession of the _Dipneusti_, Dr. Dollo regards
_Dipterus_ as the most primitive, _Scaumenacia_, _Uronemus_,
_Ctenodus_, _Ceratodus_, _Protopterus_, and _Lepidosiren_ following in
order. The last-named genus he thinks marks the terminus of the group,
neither Ganoids nor Amphibians being derived from any Dipnoans.
=Order Sirenoidei.=--The living families of _Dipneusti_ differ from
these extinct types in having the cranial roof-bones reduced in number.
There are no jugular plates and no marginal teeth in the jaws. The tail
is diphycercal in all, ending in a long point, and the body is covered
with cycloid scales. To these forms the name _Sirenoidei_ was applied
by Johannes Müller.
=Family Ceratodontidæ.=--The _Ceratodontidæ_ have the teeth above and
below developed as triangular plates, set obliquely each with several
cusps on the outer margin. Nearly all the species, representing the
genera _Ceratodus_, _Gosfordia_, and _Conchopoma_, are now extinct,
the single genus _Neoceratodus_ still existing in Australian rivers.
Numerous fragments of _Ceratodus_ are found in Mesozoic rocks in
Europe, Colorado, and India, _Ceratodus latissimus_, figured by
Agassiz in 1838, being the best-known species.
The abundance of the fossil teeth of _Ceratodus_ renders the discovery
of a living representative of the same type a matter of great interest.
[Illustration: FIG. 383.--Teeth of _Ceratodus runcinatus_ Plieninger.
Carboniferous. (After Zittel.)]
[Illustration: FIG. 384.--_Neoceratodus forsteri_ (Günther). Australia.
Family _Ceratodontidæ_. (After Dean.)]
[Illustration: FIG. 385.--Archipterygium of _Neoceratodus forsteri_
Günther.]
In 1870 the Barramunda of the rivers of Queensland was described by
Krefft, who recognized its relationship to _Ceratodus_ and gave it the
name of _Ceratodus forsteri_. Later, generic differences were noticed,
and it was separated as a distinct group by Castelnau in 1876, under
the name of _Neoceratodus_ (later called _Epiceratodus_ by Teller).
_Neoceratodus forsteri_ and a second species, _Neoceratodus miolepis_,
have been since very fully discussed by Dr. Günther and Dr. Krefft.
They are known in Queensland as _Barramunda_. They inhabit the rivers
known as Burnett, Dawson, and Mary, reaching a length of six feet, and
being locally much valued as food. From the salmon-colored flesh, they
are known to the settlers in Queensland as "salmon." According to Dr.
Günther, "the Barramunda is said to be in the habit of going on land,
or at least on mud-flats; and this assertion appears to be borne out
by the fact that it is provided with a lung. However, it is much more
probable that it rises now and then to the surface of the water in
order to fill its lung with air, and then descends again until the air
is so much deoxygenized as to render a renewal of it necessary. It is
also said to make a grunting noise which may be heard at night for some
distance. This noise is probably produced by the passage of the air
through the oesophagus when it is expelled for the purpose of renewal.
As the Barramunda has perfectly developed gills besides the lung,
we can hardly doubt that, when it is in water of normal composition
and sufficiently pure to yield the necessary supply of oxygen, these
organs are sufficient for the purpose of breathing, and that the
respiratory function rests with them alone. But when the fish is
compelled to sojourn in thick muddy water charged with gases, which are
the products of decomposing organic matter (and this must be the case
very frequently during the droughts which annually exhaust the creeks
of tropical Australia), it commences to breathe air with its lung in
the way indicated above. If the medium in which it happens to be is
perfectly unfit for breathing, the gills cease to have any function;
if only in a less degree, the gills may still continue to assist in
respiration. The Barramunda, in fact, can breathe by either gills or
lung alone or by both simultaneously. It is not probable that it lives
freely out of water, its limbs being much too flexible for supporting
the heavy and unwieldy body and too feeble generally to be of much
use in locomotion on land. However, it is quite possible that it is
occasionally compelled to leave the water, although we cannot believe
that it can exist without it in a lively condition for any length of
time.
[Illustration: FIG. 386.--Upper jaw of _Neoceratodus forsteri_ Günther.
(After Zittel.)]
"Of its propagation or development we know nothing except that it
deposits a great number of eggs of the size of those of a newt, and
enveloped in a gelatinous case. We may infer that the young are
provided with external gills, as in _Protopterus_ and _Polypterus_.
"The discovery of _Ceratodus_ does not date farther back than the year
1870, and proved to be of the greatest interest, not only on account
of the relation of this creature to the other living _Dipneusti_ and
_Ganoidei_, but also because it threw fresh light on those singular
fossil teeth which are found in strata of Triassic and Jurassic
formations in various parts of Europe, India, and America. These teeth,
of which there is a great variety with regard to general shape and
size, are sometimes two inches long, much longer than broad, depressed,
with a flat or slightly undulated, always punctated, crown, with one
margin convex, and with from three to seven prongs projecting on the
opposite margin."
[Illustration: FIG. 387.--Lower jaw of _Neoceratodus forsteri_ Günther.
(After Günther.)]
=Development of Neoceratodus.=--From DEAN'S "Fishes, Recent and
Fossil," pp. 218-221, we condense the following account (after the
observations of Dr. F. Semon) of the larval history of the Barramunda,
_Neoceratodus forsteri_:
It offers characters of exceptional interest, uniting features of
Ganoids with those of Cyclostomes and Amphibians.
The newly hatched _Neoceratodus_ does not strikingly resemble the early
larva of shark. No yolk-sac occurs, and the distribution of the yolk
material in the ventral and especially the hinder ventral region is
suggestive rather of lamprey or amphibian; it is, in fact, as though
the quantum of yolk material had been so reduced that the body form had
not been constricted off from it. The caudal tip in this stage appears,
however, to resemble that of the shark, and, as far as can be inferred
from surface views, a neurenteric canal persists. Like the shark there
then exists no unpaired fin; the gill-slits (five?) are well separated
and there is an abrupt cephalic flexure. In this stage pronephros
(primitive kidney) and primitive segments are well marked, and are
outwardly similar to those structures in Ganoid; the mouth is on the
point of forming its connection with the digestive cavity; the anus
is the persistent blastophore; the heart, well established, takes a
position, as in Cyclostomes, immediately in front of the yolk material.
In a later stage the unpaired fin has become perfectly established, the
tail increasing in length; the gill-slits have now been almost entirely
concealed by a surrounding dermal outgrowth, the embryonic operculum; a
trace of the pectoral fin appears; the lateral line is seen proceeding
down the side of the body; near the anal region the intestine[165]
becomes narrower, and the beginnings of the spiral valve appear. In a
larva of two weeks a number of developmental advances are noticed; the
fish has become opaque; the primitive segments are no longer seen; the
size of the yolk mass is reduced; the anal fin-fold appears; sensory
canals are prominent in the head region; lateral line is completely
established; the rectum becomes narrowed; and the cycloidal body-scales
are already outlined. Gill-filaments may still be seen beyond the rim
of the outgrowing operculum. In the ventral view of a somewhat later
larva the following structures are to be noted: the pectoral fins,
which have now suddenly budded out,[166] reminding one in their late
appearance of the mode of origin of the anterior extremity of urodele;
the greatly enlarged size of the opercular flap; external gills,
still prominent; the internal nares, becoming constricted off into
the mouth-cavity by the dermal fold of the anterior lip (as in some
sharks); and finally (as in _Protopterus_ and some batrachian larvæ)
the one-sided position of the anus.
The larva of six weeks suggests the outline of the mature fish; head
and sides show the various openings of the tubules of the insunken
sensory canals; and the archipterygium of the pectoral fin is well
defined. The oldest larva figured is ten weeks old; its operculum and
pectoral fin show an increased size; the tubular mucous openings,
becoming finely subdivided, are no longer noticeable; and although the
basal supports of the remaining fins are coming to be established,
there is as yet little more than a trace of the ventrals.
The early development of a lung-fish has thus far been described
(Semon) only from the outward appearance of the embryo. The egg of
_Neoceratodus_ has its upper pole distinguished by its fine covering of
pigment. From the first fine planes of cleavage it will be seen that
the yolk material of the lower pole is not sufficient to prevent the
egg's total segmentation. The first plane of cleavage is a vertical
one, passing down the side of the egg as a shallow surface furrow,
not appearing to entirely separate the substance of the blastomeres,
although traversing completely the lower hemisphere. A second vertical
furrow at right angles to the first is seen from the upper pole. The
third cleavage is again a vertical one (as in all other fishes, but
unlike _Petromyzon_), approximately meridional; its furrows appear
less clearly marked than those of earlier cleavages, and seem somewhat
irregular in occurrence. The fourth cleavage is horizontal above the
plane of the equator. Judging from Semon's figure, at this stage the
furrows of the lower pole seem to have become fainter, if not entirely
lost. In a blastula showing complete segmentation the blastomeres of
the upper hemisphere are the more finely subdivided. In the earlier
stage the dorsal lip of the blastopore is crescent-like; in the later
the blastopore acquires its oblong outline, through which the yolk
material is apparent; its conditions may later be compared to those of
a Ganoid.
The next change of the embryo is strikingly amphibian-like; the
medullary folds rise above the egg's surface, and, arching over, fuse
their edges in the median dorsal line. The medullary folds are seen
closely apposed in the median line; hindward, however, they are still
separate, and through this opening the blastopore may yet be seen.
At this stage primitive segments are shown; in the brain region the
medullary folds are still slightly separated.
In an older embryo the fish-like form may be recognized. The medullary
folds have completely fused in the median line, and the embryo is
coming to acquire a ridge-like prominence; optic vesicles and primitive
segments are apparent, and the blastopore appears to persist as the
anus. The continued growth of the embryo above the yolk mass is
apparent; the head end has, however, grown the more rapidly, showing
gill-slits, auditory, optic, and nasal vesicles, at a time when the
tail mass has hardly emerged from the surface. Pronephros has here
appeared. It is not until the stage of the late embryo that the hinder
trunk region and tail come to be prominent. The embryo's axis elongates
and becomes straighter; the yolk mass is now much reduced, acquiring a
more and more oblong form, lying in front of the tail in the region of
the posterior gut. The head and even the region of the _pronephros_ are
clearly separate from the yolk-sac; the mouth is coming to be formed.
According to Eastman (Ed. Zittel), the skeleton of _Neoceratodus_ is
less developed and less ossified than that of its supposed Triassic
ancestors. A similar rule holds with regard to the sturgeons and some
Amphibians.
[Illustration: FIG. 388.--Adult male of _Lepidosiren paradoxa_
Fitzinger. (After Kerr.)]
=Lepidosirenidæ.=--The family _Lepidosirenidæ_, representing the
suborder _Diplopneumona_, is represented by two genera of mudfishes
found in streams of Africa and South America. _Lepidosiren paradoxa_
was discovered by Natterer in 1837 in tributaries of the Amazon. It
was long of great rarity in collections, but quite recently large
numbers have been obtained, and Dr. J. Graham Kerr of the University
of Cambridge has given a very useful account of its structure and
development. From his memoir we condense the following record of its
habits as seen in the swamps in a region known as Gran Chaco, which
lies under the Tropic of Capricorn. These swamps in the rainy season
have a depth of from two to four feet, becoming entirely dry in the
southern winter (June, July).
[Illustration: FIG. 389.--Embryo (3 days before hatching) and larva (13
days after hatching) of _Lepidosiren paradoxa_ Fitzinger. (After Kerr.)]
=Kerr on the Habits of Lepidosiren.=--The loalach, as the _Lepidosiren_
is locally called, is normally sluggish, wriggling slowly about at the
bottom of the swamp, using its hind limbs in irregular alternation
as it clambers through the dense vegetation. More rapid movement is
brought about by lateral strokes of the large and powerful posterior
end of the body. It burrows with great facility, gliding through the
mud, for which form of movement the shape of the head, with the upper
lip overlapping the lower and the external nostril placed within the
lower lip, is admirably adapted. It feeds on plants, algæ, and leaves
of flower-plants. The gills are small and quite unable to supply
its respiratory needs, and the animal must rise to the surface at
intervals, like a frog. It breathes with its lungs as continuously and
rhythmically as a mammal, the air being inhaled through the mouth. The
animal makes no vocal sound, the older observation that it utters a
cry like that of a cat being doubtless erroneous. Its strongest sense
is that of smell. In darkness it grows paler in color, the black
chromatophores shrinking in absence of light and enlarging in the
sunshine. In injured animals this reaction becomes much less, as they
remain pale even in daylight.
[Illustration: FIG. 390.--Larva of _Lepidosiren paradoxa_ 30 days after
hatching. (After Kerr.)]
[Illustration: FIG. 391.--Larva of _Lepidosiren paradoxa_ 40 days after
hatching. (After Kerr.)]
[Illustration: FIG. 392.--Larva of _Lepidosiren paradoxa_ 3 months
after hatching. (After Kerr.)]
In the rainy season when food is abundant the Lepidosiren eats
voraciously and stores great quantities of orange-colored fat in the
tissues between the muscles. In the dry season it ceases to feed, or,
as the Indians put it, it feeds on water. When the water disappears the
Lepidosiren burrows down into the mud, closing its gill-openings, but
breathing through the mouth. As the mud stiffens it retreats to the
lower part of its burrow, where it lies with its tail folded over its
face, the body surrounded by a mucous secretion. In its burrow there
remains an opening which is closed by a lid of mud. At the end of the
dry season this lid is pushed aside, and the animal comes out when the
water is deep enough. When the waters rise the presence of Lepidosirens
can be found only by a faint quivering movement of the grass in the
bottom of the swamp. When taken the body is found to be as slippery as
an eel and as muscular. The eggs are laid in underground burrows in the
black peat. Their galleries run horizontally and are usually two feet
long by eight inches wide. After the eggs are laid the male remains
curled up in the nest with them. In the spawning season an elaborate
brush is developed in connection with the ventral fins.
_Protopterus_, a second genus, is found in the rivers of Africa, where
three species, _P. annectens_, _P. dolloi_, and _P. æthiopicus_, are
now known.
The genus has five gill-clefts, instead of four as in _Lepidosiren_. It
retains its external gills rather longer than the latter, and its limbs
are better developed. The habits of _Protopterus_ are essentially like
those of _Lepidosiren_, and the two types have developed along parallel
lines doubtless from a common ancestry. No fossil _Lepidosirenidæ_ are
known.
[Illustration: FIG. 393.--_Protopterus dolloi_ Boulenger. Congo River.
Family _Lepidosirenidæ_. (After Boulenger.)]
Just as the last page of this volume passes through the press, there
has appeared a bold and striking memoir on the "Phylogeny of the
Teleostomi," by Mr. C. Tate Regan of the British Museum of Natural
History. In this paper Mr. Regan takes the view that the Chondrostean
Ganoids (_Palæoniscum_, _Chondrosteus_, _Polyodon_, _Psephurus_,
etc.) are the most primitive of the Teleostomous fishes; that
the _Crossopterygii_, the _Dipneusti_, the _Placodermi_, and the
_Teleostei_ (as well as the higher vertebrates) are descended from
these; that the _Coccosteidæ_ (Arthrodires) are the most generalized
of the Placoderms, the _Osteostraci_ and most of the other forms
called Ostracophores (_Antiarcha_, _Anaspida_) being allied to the
Arthrodires, and to be included with them among the _Placodermi_;
that the cephalic appendage of _Pterichthyodes_, etc., is really a
pectoral fin; that the _Heterostraci_ (_Lanarkia_, _Pteraspis_, etc.)
are not Ostracophores or Placoderms at all, but mailed primitive
sharks, derived from the early sharks as the Chimæras are, and that
the Holostean Ganoids (_Lepisosteus_, _Amia_, etc.) should be separated
from the _Chondrostei_ and referred to the _Teleostei_, of which they
are the primitive representatives.
Mr. Regan especially calls attention to the very close similarity in
structure of pectoral and ventral fins in the Chondrostean Ganoids,
_Psephurus_ and _Polyodon_, with that of the anal fin in the same
fishes. From this he derives additional evidence in favor of the origin
of paired fins from a lateral fold. In his view, the _Chondrostei_
have sprung directly, through ancestors of the _Lysopteri_ and
_Selachostomi_, from pleuropterygian sharks (_Cladoselache_) of
the Lower Silurian, and the true fishes on the one hand and the
Crossopterygian-Dipneustan-Placoderm series on the other are descended
from these. The absence of the lower jaw in fossil remains of
Ostracophores may be due to its cartilaginous structure. "There is no
justification for regarding the _Crossopterygii_ as less specialized
than the _Chondrostei_ because they were the earlier dominant group."
These views are very suggestive and contain at least some elements
of taxonomic advance, although few naturalists of to-day will regard
the Chondrostean Ganoids as more primitive than the fishes called
_Crossopterygii_ and _Placoderms_.
These conclusions are summarized by Mr. Regan as follows:
(1) The _Chondrostei_ are the most generalized _Teleostomi_.
(2) The _Crossopterygii_ differ from them
(_a_) in the lobate pectoral fin;
(_b_) in the larger paired gular plates.
(3) The _Placodermi_ (_Coccosteidæ_, _Asterolepidæ_,
_Cephalaspidæ_) are a natural group, not related to the
_Heterostraci_, which are _Chondropterygii_. They may probably
be regarded as armored _primitive Crossopterygii_, this view
being most in accordance with
(_a_) the arrangement of the cranial roof-bones in _Coccosteus_;
(_b_) the structure of the ventral fin in _Coccosteus_;
(_c_) the structure of the pectoral limb of the _Asterolepidæ_.
(4) The _Dipneusti_ probably originated from more specialized
_Crossopterygii_, e.g., from the neighborhood of the
_Holoptychiidæ_.
(5) The Teleostei differ in so many respects from the _Chondrostei_
that they should rank as an order, in which the _Holostei_ are
included.
FOOTNOTES:
[164] This group has been usually known as _Dipnoi_, a name chosen
by Johannes Müller in 1845. But the latter term was first taken by
Leuckart in 1821 as a name for Amphibians before any of the living
_Dipneusti_ were known. We therefore follow Boulenger in the use of the
name _Dipneusti_, suggested by Hæckel in 1866. The name Dipnoan may,
however, be retained as a vernacular equivalent of _Dipneusti_.
[165] The yolk appears to be contained in the digestive cavity, as in
_Ichthyophis_ and lamprey.
[166] The abbreviated mode of development of the fins is most
interesting; from the earliest stage they assume outwardly the
archipterygial form; the retarded development of the limbs seems
curiously amphibian-like; the pectorals do not properly appear until
about the third week, the ventrals not until after the tenth.
The Natural History of Plants
THEIR FORMS, GROWTH, REPRODUCTION
AND DISTRIBUTION
FROM THE GERMAN OF
ANTON KERNER VON MARILAUN
_Professor of Botany in the University of Vienna_
BY F. W. OLIVER
_Quain Professor of Botany in University College, London_
WITH THE ASSISTANCE OF
MARIAN BUSH AND MARY E. EWART
4to. New edition. 2 vols. The set--$11.00
A work for reference or continuous reading, at once popular and, in the
modern sense, thoroughly scientific. The new edition is practically
identical with the former four-volume edition except that the colored
plates in the latter have been omitted. The wood-engravings, over two
thousand in number, have been retained.
_Prof. John M. Coulter_, in THE DIAL: "Prof. Kerner has brought the
most recent researches within reach of the intelligent reader, and in
a style so charming that even the professional teacher may learn a
lesson in the art of presentation.... =It is such books as this that
will bring botany fairly before the public as a subject of absorbing
interest=; that will illuminate the botanical lecture-room."
_Prof. Chas. R. Barnes_, in THE BOTANICAL GAZETTE: "This lucidity, and
the excellent illustrations, not only will introduce the non-botanical
reader to the science of botany, but =should serve as a lesson to the
professional botanist in the art of presentation=."
_The Nation_: "He has succeeded in constructing a popular work on the
phenomena of vegetation which is practically without any rival."
GUIDE TO THE STUDY OF INSECTS
AND A TREATISE ON THOSE
INJURIOUS AND BENEFICIAL TO CROPS
FOR THE USE OF
_COLLEGES, FARM-SCHOOLS AND AGRICULTURISTS_
BY ALPHEUS S. PACKARD, M.D.
With 685 illustrations. Ninth edition. xii+715 pp., 8vo, $5.00 net
PLANT PHYSIOLOGY
BY GEORGE J. PEIRCE
_Professor in Leland Stanford University_
vi+291 pages, 8vo $2.00
A modern and thoroughly scientific discussion of the general principles
of plant physiology, intended for the student or general reader
acquainted with the elements of botany.
_Science_: "The volume is full of original suggestions and differs
quite markedly from the old-time works devoted to plant physiology."
_William F. Ganong, Professor in Smith College_: "I am much pleased
with the clearness, proportion, and vigor with which it treats the
subject. It seems to me =an admirable exposition of the principles of
plant physiology= as they are understood at the present day, and it
should have a wide use."
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Henry Holt and Company
29 West 23d Street, New York
GEOLOGY
Vol I. "Geologic Processes and Their Results"
BY Prof. THOMAS C. CHAMBERLIN
AND
Prof. ROLLIN D. SALISBURY
Heads of the Departments of Geology and Geography, University of
Chicago; Members of the United States Geological Survey; Editors of
the Journal of Geology
With numerous illustrations, including 24 colored maps and
3 tables. 654 pages, 8vo, $4.00 net
Vol. II. "Earth History." _In preparation_
CHAS. D. WALCOTT, _Director of U. S. Geological Survey_: "I am
impressed with the admirable plan of the work and with the thorough
manner in which geological principles and processes and their results
have been presented. The text is written in an entertaining style
and is supplemented by admirable illustrations, so that the student
cannot fail to obtain a clear idea of nature and the work of geological
agencies, of the present status of the science, and of the spirit which
actuates the working geologist."
T. A. JAGGAR, Jr., _Harvard University_: "An excellent statement of
modern American geology, with abundant new illustrative material based
upon the most recent work of government and other surveys."
HENRY S. WILLIAMS, _Yale University_: "It is the best treatise on this
part of the subject which we have seen in America."
R. S. WOODWARD, _Columbia University_: "It is admirable for its
science, admirable for its literary perfection, and admirable for its
unequalled illustrations."
ISRAEL C. RUSSELL, _University of Michigan_. "I deem it an epoch-making
book and one that will vastly extend the study of geology."
BUTTERFLIES
BY S. H. SCUDDER
THEIR STRUCTURE, CHANGES, AND LIFE-HISTORIES
_With Special Reference to American Forms. Being an Application
of the "Doctrine of Descent" to the Study of Butterflies. With an
Appendix of Practical Instruction_
12mo $1.50 net
Brief Guide to the Commoner Butterflies of the Northern
United States and Canada
Being an Introduction to the Knowledge of their Life-Histories
_New edition. With 21 plates, containing in all 97 illustrations_
12mo $1.50
THE LIFE OF A BUTTERFLY
A CHAPTER IN NATURAL HISTORY FOR THE GENERAL READER
16mo $1.00
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Henry Holt and Company
29 West 23d Street New York
FERNS
A MANUAL FOR THE NORTHEASTERN STATES
WITH ANALYTICAL KEYS BASED ON THE
STALKS AND ON THE FRUCTIFICATION
_With over two hundred illustrations from original drawings and
photographs_
BY CAMPBELL E. WATERS
302 pages, square 8vo. Boxed, $3.00 net; by mail, $3.34
This book is thoroughly authoritative, and is written in popular style.
It covers all the ferns in the region embraced either in Britton's or
in Gray's Manuals.
"This book is likely to prove the leading popular work on ferns. =No
finer examples of fern photography have ever been produced.= Dr. Waters
brings to his work fifteen years of experience in field and herbarium
study, and the book may be expected to prove of permanent scientific
value, as well as to satisfy a want which existing treatises have but
imperfectly filled."--_Plant World._
"For all who study or wish to study our native ferns Dr. Waters has
prepared a book which is sure to prove =both helpful and inspiring=.
Especially charming and significant are the views showing typical
habits and habitats."--_The American Naturalist._
"There could hardly be a better book for those interested in the
subject."--_Boston Literary World._
OUR NATIVE FERNS
AND THEIR ALLIES
_WITH SYNOPTICAL DESCRIPTION OF THE AMERICAN PTERIDOPHYTA
NORTH OF MEXICO_
BY LUCIEN M. UNDERWOOD
PROFESSOR IN COLUMBIA UNIVERSITY
Revised. xii+156 pages, 12mo $1.00
"The elementary part is clear and well calculated to introduce
beginners to the study of the plants treated of. The excellent key
makes the analysis of ferns comparatively easy. The writer cordially
commends the book. It should be in the hands of all who are especially
interested in the vascular cryptogams of the United States."--_Bulletin
of the Torrey Botanical Club, N. Y._
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Henry Holt and Company
29 West 23d Street, New York
MUSHROOMS
BY GEORGE FRANCIS ATKINSON
_Professor of Botany in Cornell University, and Botanist of the
Cornell University Experiment Station_
=Recipes for Cooking Mushrooms.= By MRS. SARAH TYSON RORER
=Chemistry and Toxicology of Mushrooms.= By J. F. CLARK
_With 230 illustrations from photographs, including 15 colored
plates_
320 pages, 8vo. $3.00 net; by mail, $3.23
_Educational Review_:--"It would be difficult to conceive of a
more attractive and useful book.... In addition to its general
attractiveness and the beauty of its illustrations, it is written in a
style well calculated to win the merest tyro."
Moulds, Mildews, and Mushrooms
BY LUCIEN M. UNDERWOOD
_Professor in Columbia University_
iv+236 pages, 12mo $1.50
_Bradley M. Davis_, in the BOTANICAL GAZETTE:--"Wonderfully free from
the dry diagnoses of most systematic descriptions, and everywhere
combined with interesting accounts of life-habits and activities.... A
marvel in its compactness, with a wonderfully uniform tone throughout,
condensed and yet very clear."
Flora of the Northern States and Canada
BY PROFESSOR N. L. BRITTON
_Director of the New York Botanical Garden_
x+1080 pages, large 12mo $2.25
This manual is published in response to a demand for a handbook
suitable for ordinary school use, which shall meet modern requirements
and outline modern conceptions of the science. It is based on _An
Illustrated Flora_ prepared by Professor Britton in co-operation with
Judge Addison Brown, in three volumes. The text has been revised
and brought up to date, and much of novelty has been added, but all
illustrations are omitted.
CONWAY MACMILLAN, _Professor in the University of Minnesota_, in
SCIENCE:--"There is no work extant in the whole series of American
botanical publications which deals with descriptions of the flowering
plants that can for a moment be compared with it, either for a skillful
and delightful presentation of the subject-matter or for modern,
scientific, and accurate mastery of the thousandfold mass of detail of
which such a work must consist."
V. M. SPALDING, _Professor in the University of Michigan_:--"I regard
the book as one that we cannot do without and one that will henceforth
take its place as a necessary means of determination of the plant
species within its range."
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Henry Holt and Company
29 West 23d Street, New York
Transcriber's Notes:
Simple spelling, grammar, and typographical errors were corrected.
Punctuation normalized.
Anachronistic and non-standard spellings retained as printed.
The ERRATA on p. ix has been corrected in the text.
P. xxiii corrected "_Salmo gairdneri_, the Steelhead Trout. 326" to
"_Salmo irideus_, the Rainbow Trout. 326" to agree with the actual
illustration caption.
P. xxiii corrected "_Salmo rivularis_, the Steelhead Trout. 327"
to "_Salmo gairdneri_, the Steelhead Trout. 327" to agree with the
actual illustration caption.
Italics markup is enclosed in _underscores_.
Bold markup is enclosed in =equals=.
Greek text is transliterated and enclosed in ~tildes~.
Proofreading Symbols for Diacritical Marks
(In the table below, the "x" represents a letter with a
diacritical mark.)
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macron (straight line) ¯ [=x] [x=]