which the species known to Linnæus belong, there are two aberrant forms,
each represented by a single species. These are the little _Tarsius_ of
Borneo and Celebes, and the singular _Chiromys_, or Aye-aye, which,
though an inhabitant of the headquarters of the group, Madagascar, and
living in the same forests and under the same conditions as the most
typical lemurs, exhibits a most remarkable degree of specialisation in
the structure both of limbs and teeth, the latter being modified so as
to resemble, at least superficially, those of the Rodents, a group with
which in fact it was once placed. It was discovered by Sonnerat in
Madagascar in 1780, two years after the death of Linnæus. The specimen
brought to Paris by this traveller was the only one known until 1860.
Since that date, however, its native land has been more freely open than
before to explorers, and many specimens have been obtained, one having
lived for several years in the Gardens of the London Zoological Society.
The history of a name is often not a little curious. Linnæus applied the
term _Lemures_, _i.e._ the departed spirits of men, to these animals on
account of their nocturnal habits and ghost-like aspect. The
hypothetical continent in the Indian Ocean, supposed to have connected
Madagascar with the Malayan Archipelago is called by Mr. Sclater,
_Lemuria_, as the presumed original home of the lemur-like animals.
Although the steps are not numerous, it might puzzle a classical
scholar, ignorant of Zoology, to explain the connection between this
continent and the Roman festival of the same name.
The fifth animal which Linnæus places in his genus _Lemur_, under the
name of _L. volans_, is the very singular creature to which the generic
term _Galeopithecus_ has since been applied. It is one of those
completely aberrant forms which, having no near existing relations, and
none yet discovered among extinct forms, are perfect puzzles to
systematic zoologists. It is certainly not a lemur, and not a bat, as
has been supposed by some. We shrink from multiplying the orders for the
sake of single genera containing only two closely-allied species; so we
have generally allowed it to take refuge among the _Insectivora_, though
without being able to show to which of that somewhat heterogeneous group
it has any near affinities.
The fourth genus of the PRIMATES is _Vespertilio_, comprising six
species of bats. This genus has now by universal consent expanded into
an order, and one of the best characterised and distinctly circumscribed
of any in the class: indeed, those who have worked most at the details
of the structure of bats find so much diversity in the characters of the
skull, teeth, digestive organs, etc., associated with the modification
of the fore-limbs for flight common to all, as almost to entitle them to
be regarded rather as a sub-class. Anatomical as well as palæontological
evidence shows that they must have diverged from the ordinary mammalian
type at a very far distant date, as the earliest known forms, from the
Eocene strata, are quite as specialised as any now existing, and no
trace has hitherto been discovered of forms linking them to any of the
non-volant orders. By the publication within the last few weeks of a
valuable monograph on the existing species of the group, entitled “A
Catalogue of the Chiroptera in the Collection of the British Museum,” by
G. E. Dobson, we are enabled to contrast our present knowledge with that
of the time of Linnæus. Although the author has suppressed a large
number of nominal species which formerly encumbered our catalogues, and
wisely abstained from the tendency of most monographists to multiply
genera, he describes four hundred species, arranged in eighty genera;
nearly double the number of species, and exactly double the number of
genera, of the whole class MAMMALIA in the _Systema Naturæ_, and these
Dr. Günther remarks in his Preface are probably only a portion of those
existing. The small size, nocturnal habits, and difficulty of capture of
these animals, are sufficient reasons for the supposition that there
are still large numbers unknown to science. In the list of Linnæus, the
first primary group of Dobson, the _Megachiroptera_, now containing
seventy species, is represented by a single one, _V. vampyrus_,
obviously a _Pteropus_, to which the bloodthirsty habits of the fabulous
Vampyre are attributed, but which is not absolutely identified with any
one of the known species. The other species described by Linnæus can
almost all be identified with bats at present well known.
A curious example of the results of basing classification upon a few,
and those somewhat artificial characters, is afforded by one of the true
bats, now called _Noctilio leporinus_, though admitted by Linnæus to be
“_simillimus vespertilionibus, similiter pedibus alatus_, being
separated from the others, not only generically, but even placed in
another order, that of the GLIRES or Rodents, because it did not, or was
supposed not to fall under the definition of the order PRIMATES, which
begins “_Dentes primores incisores superiores IV. paralleli_.” In
reality this bat has four upper incisors, but the outer ones are so
small as to have been overlooked when first examined. But even if this
were not so, no one would now dream of basing an animal’s position upon
such a trivial character when opposed to the totality of its
organisation and habits.
The characters of the incisor teeth are placed in the first rank in the
definitions of all the orders in the _Systema Naturæ_, and hence the
next order called BRUTA, characterised by “_dentes primores nulli
superius aut inferius_,” contains a curious mixture of heterogeneous
animals, as the names of the genera _Elephas_, _Trichechus_, _Bradypus_,
_Myrmecophaga_, _Manis_, and _Dasypus_ will indicate. It contains, in
fact, all the animals then known comprised in the modern orders of
_Proboscidea_, _Sirenia_, and _Edentata_, together with the walrus, one
of the _Carnivora_. The name BRUTA has been revived for one of these
orders, that more generally called _Edentata_, but I think very
inappropriately, for it was certainly not equivalent, and if retained at
all, should rather belong to the _Proboscidea_, as _Elephas_ stands
first in the list of genera which Linnæus assigned to the group.
It is curious to find that the striking differences between the African
and the Indian elephants, now so well understood by every beginner in
Zoology, and all the facts which have already been accumulated relating
to the numerous extinct forms of Proboscideans, whether Mammoths,
Mastodons, or Dinotheria, were quite unknown to Linnæus. One species
only, _Elephas maximus_, represented in the zoology of a hundred years
ago all that was known of the elephants or elephant-like animals.
The genus _Trichechus_ of this edition exhibits a very curious phase of
zoological knowledge. It contains two species--1. _T. rosmarus_, the
walrus, now known to be a modified seal, and therefore a member of the
Linnæan order FERÆ, and 2. _T. manatus_, a name under which were
included all the known forms of manatees and dugongs, in fact the whole
of the modern order _Sirenia_,--animals widely removed in all essential
points of their organisation from the walrus, with which they are here
generically united. Their position, however, between the elephant on the
one hand and the sloths on the other, is far better than their
association with the _Cetacea_, as in Cuvier’s system, an association
from which it has been most difficult to disengage them, notwithstanding
their total dissimilarity except in a few external characters. Although
the discovery of many fossil forms has done much to link together the
few existing species and to show the essential unity of the group, it
has thrown no light upon their origin, or their affinities to other
mammals. They still stand, both by their structure and their habits, in
a strangely isolated position, and it baffles conjecture to say whence
they have been derived, or how they have attained their present singular
organisation.
The remaining genera of the Linnæan order BRUTA constitute the group out
of which Cuvier, following Blumenbach, formed his order _Edentata_, a
name certainly not happily chosen for a division which includes species
like the great armadillo, having a larger number of teeth than any other
land mammal, but which, nevertheless, has been so generally adopted, and
is so well understood, that to attempt to change it would only introduce
an element of confusion. Four out of five of the principal modifications
of form in the group at present known are indicated by the four Linnæan
genera, _Bradypus_ or sloth, _Myrmecophaga_ or ant-eater, _Manis_ or
pangolin, and _Dasypus_ or armadillo. The advances during the century
have consisted in the accumulation of a great mass of details respecting
these groups; the addition of a fifth and very distinct existing form,
the _Orycteropus_ or Cape ant-eater; and the discovery of numerous and
very remarkable extinct forms, such as the Megatheriums and Glyptodons
of South America, now so fully known by their well-preserved osseous
remains. There is, however, still much to be done in working out the
real relationship of the somewhat isolated members of the order, if it
be a natural order, both to each other, and to the rest of the Mammalia,
from which they stand widely removed in many points of organisation.
The third order of Linnæus, FERÆ, contained all the then known animals,
which, with whatever diversities of general structure, agreed in their
predatory habits, and possessed certain general characters of teeth and
claws to correspond, though the terse definition of “_Dentes primores
superiores sex, acutiusculi canini solitarii_,” is by no means
universally applicable to them. This order was broken up by Cuvier into
the orders _Carnivora_ and _Insectivora_, and the genus _Didelphys_,
included in it by Linnæus, has been since by universal assent removed to
another group.
The first six genera belong to the very well-defined and probably
natural group now called _Carnivora_. The one placed at the head of the
list, _Phoca_, is equivalent to the large and important modern sub-order
_Pinnipedia_,--the walrus, however, though essentially a seal, having
been, as before mentioned, relegated by Linnæus to another order, on
account of its aberrant dentition. But three species are recorded in the
genus; _P. ursina_, the sea-bear of the North Pacific (now _Otaria
ursina_); _P. leonina_, founded on Anson’s sea-lion, now commonly called
the elephant seal, or sea-elephant (_Macrorhinus proboseideus_, or more
properly _leoninus_); and _P. vitulina_, the common seal of our coasts.
The terrestrial sub-order of _Carnivora_ is represented by five genera:
1. _Canis_, including the dog, wolf, hyæna, fox, arctic fox, jackal,
etc. 2. _Felis_, with only six species, but still one of the few Linnæan
genera, which covers exactly the same ground as at present in the
opinion of the majority of zoologists, although it may be mentioned as
an example of the tendency towards excessive and unnecessary
multiplication of generic names which exists in some quarters, that it
has been divided into as many as fourteen. 3. _Viverra_, a heterogeneous
group, containing ichneumons, coatis, and skunks, animals belonging to
three very distinct families, according to modern ideas. 4. _Mustela_, a
far more natural group, being nearly equivalent to the modern family
_Mustelidæ_; and, lastly, a very comprehensive genus _Ursus_, consisting
of _U. meles_, the badger, _U. lotor_, the raccoon, _U. luscus_, the
wolverene, and all the true bears known, comprised in the single species
_U. arctos_. Many interesting forms of _Carnivora_, as _Cryptoprocta_,
_Proteles_, _Eupleres_, _Ailurus_, and _Ailuropus_, have no place in the
Linnæan system, being comparatively modern discoveries. The very recent
date (1869) at which the last-named remarkable animal was made known to
science by the enterprising researches of the Abbé David into the Fauna
of Eastern Thibet, gives hope that we may not yet be at the end of the
discovery of even large and hitherto unsuspected forms of existing
mammals.
Next in the Linnæan system comes the genus _Didelphys_, constituted for
the reception of five species of American opossums. This is a very
interesting landmark in the history of the progress of the knowledge of
the animal life of the world, as these five opossums, forming a genus in
the midst of the order FERÆ, were all that was then known of the great
sub-class _Marsupialia_, now constituting a group entirely apart from
the ordinary members of the class. It is difficult now to imagine an
animal world without kangaroos, without wombats, without phalangers,
without thylacines, without dasyures, and so many other familiar forms,
and yet such was the animal world known to Linnæus. It is true that a
species of kangaroo from one of the islands of the Austro-Malayan
Archipelago was described as long ago as 1714 by De Bruyn, who saw it
alive at the house of the Dutch governor of Batavia, and that Captain
Cook and Sir Joseph Banks saw and killed kangaroos on the east coast of
Australia in 1770, and had published figures and descriptions of them in
1773, or five years before the death of Linnæus; but the work we are
now considering contains no traces of knowledge of the existence of such
a remarkable and now so well-known animal.
The three remaining genera of FERÆ, _Talpa_, _Sorex_, and _Erinaceus_,
contained all the known species of the present order INSECTIVORA, which
now embraces many and very varied forms, quite unsuspected a century
ago, and to which it is probable that many others will be added by the
time the exploration of the animal products of the world is completed.
The fourth order, GLIRES, has remained practically unchanged to our day,
although the name _Rodentia_ has generally superseded that bestowed upon
it by Linnæus. The five genera of the _Systema Naturæ_, _Hystrix_,
_Lepus_, _Castor_, _Mus_, and _Sciurus_, have been vastly increased,
partly by subdivision and partly by the discovery of new forms.
_Noctilio_ is, as before mentioned, removed to the Chiroptera, but its
loss is well compensated for by _Hydrochærus_, the well-known Capybara,
the largest existing member of the group, which in the Linnæan system is
placed among the Belluæ, in the same genus with the pigs.
The fifth Linnæan order, PECORA, is a fairly natural group, equivalent
to Cuvier’s _Ruminantia_; but it is no longer considered of the value of
an order, since the animals composing it have now been shown to be as
closely related to certain of those belonging to the next order as they
are to each other. The first genus, _Camelus_, contains both the
American lamas and the Old World camels, the demonstration of the common
origin and close affinities of which has been one of the important
results of the recent discoveries in the palæontology of the Western
continent. In the next genus, _Moschus_, were placed the well-known musk
deer of the highlands of Central Asia, and two small African antelopes,
which have no special affinity with it. The subsequent inclusion in the
same genus of the small chevrotains (_Tragulinæ_), which was very
natural at the time, as they agree perfectly with the musk in the
absence of horns and the presence of large canine tusks, by which
artificial characters the genus was defined by Linnæus, was one of those
unfortunate associations which have greatly retarded the progress of
knowledge of the true affinities of the group. Judging by the popular
works on Zoology, it is still as difficult to apprehend that a
chevrotain is not a musk deer, as it is that a manatee is not a
cetacean,--both errors of the same kind, if not quite so gross, as that
of regarding a whale as a fish, or a bat as a bird. The Linnean genus
_Cervus_ contains six species of true deer, including the moose,
reindeer, red deer, fallow, and roe, associated with the giraffe.
The twenty-one species of the great group of hollow-horned Ruminants, at
that time recognised, are distributed quite arbitrarily in three genera,
_Capra_, _Ovis_, and _Bos_. Though subsequent investigations have
greatly increased the number of species known, we are still in much
uncertainty about their mutual affinities and generic distinctions.
Being a group of comparatively modern origin, and only just attaining
its complete development, variation has chiefly affected the less
essential and superficial organs. Moreover, the process of extinction of
intermediate forms has not operated sufficiently long to break it up
into distinctly-separated natural minor groups, as is the case with many
of the older families, which lend themselves, therefore, far more
readily to systematic classification, especially as long as the extinct
forms are unknown or ignored.
The sixth order of land mammals, BELLUÆ, corresponding to the
_Pachydermata_ of Cuvier, contains what is now known to be a
heterogeneous collection, viz. the horses, the hippopotamus, the pigs,
rhinoceroses, and the rodent capybara. The abolition of these two last
orders and the entire rearrangement of the ungulate mammals into two
different natural groups, now called _Artiodactyla_ and
_Perissodactyla_, first indicated by Cuvier in the “Ossemens fossiles,”
from the structure of the limbs alone, and afterwards confirmed by Owen
from comparison of every part of the organisation, has been one of the
most solid advances made in our knowledge of the classification of the
Mammalia during the present century.
The past history of this, as of so many other groups of vertebrated
animals, has been brought to light in an unexpected manner by the
wonderful discoveries of fossil remains made during the last ten years
in the Rocky Mountains of America,--discoveries, the importance of which
will only be fully appreciated when the elaborate and beautifully
illustrated work which Professor Marsh has now in progress is completed.
The last Linnæan order, CETE, is exactly conterminous with the order so
named, or rather more generally modified to _Cetacea_, in the best
modern systems, for Linnæus did not commit the error of Cuvier and
others, of including the _Sirenia_ among the whales. His knowledge of
the animals composing the group was necessarily very imperfect; indeed
it is only within the last few years, especially since the impulse given
to their study by Eschricht of Copenhagen, that the great difficulties
which surround the investigation of the structure and habits of these
denizens of the open sea have been so far surmounted that we have begun
to obtain clear views of their organisation, affinities, and
geographical distribution.
Two most remarkable forms of mammals, so abnormal in their organisation
as now to be generally considered deserving the rank of a distinct
sub-class, the _Echidna_ and _Ornithorhynchus_, were first made known to
science in 1792 and 1799 respectively, and consequently have no place in
the _Systema Naturæ_. The very recent discovery of a third form to this
group, or at least a very striking modification of one of the forms, the
large New Guinea echidna (_Acanthoglossus bruynïi_), is the last
important acquisition to our knowledge of the class.
In this brief review of the progress of one small section of one branch
of zoological knowledge, it will be seen that it is chiefly of systems
of arrangement, of classification, and of names, that I have been
treating. By many biologists of the present day these are looked upon as
the least attractive and least profitable branches of the subject. The
interest of classification, though it has lost much in some senses by
the modern advances of scientific biology, has, however, gained vastly
in others. The idea that has now, chiefly in consequence of the writings
of Darwin, taken such strong hold upon all working naturalists--the idea
of a gradual growth and progressive evolution, and therefore genetic
connection between all living things--breaks down the artificial
barriers which zoologists raise around their groups, and shows that such
names as _species_, _genera_, _families_, _orders_, etc., are merely
more or less clumsy attempts to express various shades of differences
among creatures connected by infinite gradations, and in this sense
destroys the importance attached to them by our predecessors. On the
other hand, it immensely increases the interest contained in the word
“relationship,” as it implies that the word is used in a real and not,
as formerly, in a metaphorical sense. There is a kind of classification,
such as we might apply to inanimate substances or manufactured articles.
We may say, for instance, that a tumbler, a wine-glass, and a tea-cup
are more closely related to each other than either one is to a chair or
a table, and that they might be formed into one group, and the
last-named objects be placed in a second. This kind of classification is
certainly useful in its way for methodical arrangement and descriptive
purposes. It is the kind of arrangement which Linnæus and his
contemporaries applied to animals. It is, however, a very different
classification from that which supposes that the members of a group
having common essential characters are descended from a common ancestor,
and have gradually, by whatever cause or means, become differentiated
from other groups. On this view a true classification, if it could be
obtained, would be a revelation of the whole secret of the evolution of
animal life, and it is no wonder that many are willing to devote so
large a share of their energies in an endeavour to attain it.
The right application of the principles of nomenclature, first clearly
established by Linnæus, to the groups we form is, again, by no means to
be despised, as laxity and carelessness in this respect are becoming
more and more the greatest hindrances to the study of Zoology. The
introduction of any new term, especially a generic name, and indeed the
use of an old one by any person whose authority carries weight, has an
appreciable effect upon the progress of science, and should never be
made without a full sense of the responsibility incurred. All beginners
are puzzled and often repelled by the confused state of zoological
nomenclature to an extent to which those who have advanced so far as
only to care for the things, and to whom the actual names by which they
are called are comparatively indifferent, have little idea. Those whose
special gift or inclination leads them to the pursuit of other branches
of Biology, as Morphology, Physiology, or Embryology, must have definite
names for the objects they observe, depict, or describe, and are
dependent upon the researches of the systematic zoologist for supplying
them, and should not neglect to take his counsel, otherwise much of
their work will lose its value.