66 
FIRST CLASS OF THE VERTEBRATED ANIMALS. 
together all the known species of this genus, and then taking the mean of their di- 
mensions, M. Isidore Geoffrey found that the largest species only exceeded this mean 
by an inch and a quarter, while the smallest remained below the average by an equal 
quantity. If, however, the Ooistitis be subdivided into those three sections usually 
received by Naturalists, then the dimensions of the species belonging to each section 
will differ from the medium magnitude proper to that section only by six lines one 
way or another. 
Among the Bats the genus Vespertilio, as formerly established, would seem at 
first sight to present a striking exception to this rule, in respect to the Roussettes, 
in which the distance between their expanded wings is four feet, while the smaller 
species of this country scarcely measure as many inches. But upon investigating the 
characters upon which the genus had been instituted, M. Geoffroy observed several 
important points of difference between the organization of the larger and the smaller 
Bats, which have ultimately led to their being separated into distinct subdivisions and 
genera. IVIany other apparent exceptions have also vanished in a similar manner on 
being examined more minutely, and the consequence has been, that several new 
Genera have been adopted by the general consent of Naturalists. Indeed, it may be 
stated generally, that wherever there have existed striking differences of size between 
nearly-allied species. Naturalists have always felt the necessity of establishing sub- 
genera, or groups in w hich these remarkable anomalies are made to disappear. 
Since it thus appears that the sizes of the Mammalia bear a determinate relation 
to those external characters which usually serve to determine the Genera or higher 
divisions, it will follow that their magnitude must bear a corresponding relation to 
the conditions of their existence, such as the element in which they move, their mode 
of life, their food, their climate, and their situation. In all these respects we may 
expect to find that their sizes will bo so apportioned by Nature, as to bring them into 
harmonious correspondence with the circumstances of their condition. 
In reference to the element in which they move, we find that all those Mammalia 
which dwell in the bosom of the ocean acquire the largest dimensions. The different 
species of VNTjale (Salana)^ of Cachalot CPht/seter)f and of Dolphin (Dtlphinm')^ 
attain a bulk to which few other IVIammalia can compare. Even among those groups 
of Mammalia where some genera commonly frequent the water, and others live habi- 
tually on the land, wc find that the former attain to a magnitude much greater than 
that of the latter. Thus, among the Camassiers, no species reaches so great a size 
as the Sea-Horse or Morse (TncAecAiw roswartts). Again, among the numerous 
animals composing the Genus Mustela of Linnteus, the Weasels, Martins, and other 
terrestrial species, are much smaller than the Otters. Even among the Otters 
it is precisely those species which are the most essentially aquatic, such as 
the Brazilian Otter (X. Brazilienins')^ and the Sea-Otter (Z/. luiris), which attain 
the greatest dimensions. The same observation is also applicable to the Rodentia 
and Insectivora. The Beaver is larger than the Mouse, and the Water Shrew (^Sorex 
Jodiens) of greater magnitude than the common Shrew (S', uraneua), and for a si- 
milar reason. This adaptation of Nature seems obviously intended to accommodate 
their bodies to the density of the medium in which they more habitually reside. A 
greater bulk, by displacing a larger quantity of water, renders them more buoyant, 
and leaves the muscular force of their limbs more unfettered to execute the movements 
proper to each animal- Again, the force of gravity at the earth’s surface being 
counteracted in a more sensible degree by the reaction of the denser fluid, enables 
some of the aquatic species to attain a bulk which would be impossible in a land 
animal. 
On the other hand, those Mammalia which live more exclusively in the air, such 
as the Bats, or upon trees, like the greater part of the Monkeys, never attain any 
very considerable dimensions. The agility which their situation requires would have 
been inconsistent with a heavy form, and the dimensions of the trees in which most 
Quadrumana fix their abodes, necessarily confine their magnitude within very nar- 
row limits. Among the remaining Mammalia which commonly live on the surface 
of the land, and may thence be more particularly denominated terrestrial Mammalia, 
wc find that their average bulk maintains a size intermediate to these lighter forms 
of the aerial Mammalia on the one hand, and those belonging to the more ponderous 
inhabitants of the ocean on the other. The relative magnitude depends, however, 
with the terrestrial Mammalia, upon certain other conditions; for, while we find some 
animals among them which only yield in magnitude to the aquatic tribes, wo at the 
same time discover in this division tlio very smallest animals of the entire class with- 
out exception. This rule, therefore, does not hold so accurately in respect to those 
animals which dwell habitually on the ground. 
If, however, we investigate the terrestrial and aerial Mammalia in reference to the 
nature of their food, wo. find certain constant relations established by Uie Creator between 
the quantity of food necessary for their maintenance and that which is supplied to them ; 
in other words, between the demand of their stomachs and the supply of food suffi- 
cient to sustain them. The largest of all terrestrial IMaramalia are the Herbivorous 
animals, such as the Elephant, Hippopotamus, and Rhinoceros, because the grosser 
kinds of vegetable food are supplied in immense quantities throughout many parts of 
the globe, but especially in the tropical climates. The warmer regions of the globe 
yield, in a dense and luxurious vegetation, an ample supply of nourishment to these 
ponderous frames; and supply those succulent plants, soft stems, and leaves, the 
want of which renders the regions around the poles wholly incapable of supporting the 
larger terrestrial Mammmia. In the group of Herbivorous Mammalia, while wc have 
the colossal magnitude of the Elephant on the one hand, wo have on the other the 
Java -Musk (Moschu^ meminajy scarcely the size of a Rabbit. 
The Carnivorous Mammalia compose a group which forms, after the preceding, a 
series of an inferior order. Among them wc have the Lion and the Tiger for the 
maxitnum, and find a minimum limit probably in the Lrmino (Mustela enninea). 
Although these animals find an abundant supply of nourishment among the inferior 
tribes of every denomination, it is neither so ample nor so constant as to permit them 
to attain any very great dimensions. An unwieldy bulk would ill correspond with 
that activity which their predatory habits seem ne''.cssarily to require. 
The Frugivorous tribes of Mammalia form a third group confined within much nar- 
rower dimensiuns. On the one hand wc have the OrangSi and on llie other the 
smallest species of Roussette Bats (Pteropus). These species arc accordingly con- 
fined to those more favored regions of the earth, where fruits are to be fomid 
throughout all seasons of the year. 
Lastly, we see among those Mammalia which feed exclusively on Insects a further 
instance of the relation which the nature of the food bears to the average bulk of 
species. While we have the Ant-eaters (Mprmeeopkaga and Orycteropus), whose 
length does not exceed four feet, we have, in the minute Shrews, some of the smallest 
of known Quadrupeds. 
Thus, upon considering all the Mammalia, in a general point of view, in reference 
to their comparative dimensions, wo are led to perceive that there always exists a re- 
lation between the bulk of the animals composing an entire group and the conditions 
of their diet. The more capacious animals feed upon those substances which are 
found most abundantly on the face of the globe. Those of smaller size usually attain 
to dimensions proportional either to the magnitude of the animals upon which they 
are destined to feed, or to the nature of those vegetable substances to which, their 
digestive organs are adapted. Every where we perceive a most exact correspondence 
between the quantity of nourishment which their constitution requires, and that which 
is bestowed by the hand of Nature. This method of apportioning to each animal, by 
an equitable division, its share of the produce of the earth, is surely one of the most 
admirable and beneficent arrangements of the Creator. 
Although the subject of the Geographical distribution of the Slammalia will here- 
after receive our most attentive consideration, it may be proper to remark at present, 
that the dimensions of animals always bear a certain relation to the magnitude of the 
regions in which they reside. It has long been remarked, that islands which are 
cither very small or much isolated contain very few Quadrupeds, and those only of 
small dimensions, while some arc even wholly destitute of Mammalia. Indeed, the 
largest animals of this class are found only upon the continents, in the largest islands, 
or upon those smaller islands which are so near to the larger continents as to be inti- 
mately affected by their proximity. Even in respect to the continents themselves, 
the Mammalia belonging to the Old Continent, which is the larger, surpass in dimen- 
sions those of the American, which is the smaller. The Mammalia of New Holland 
come next in magnitude, then those of Jladagascar, Britain, and the lesser islands. 
A similar law may be traced among the aquatic Mammalia, for those w hich inhabit 
the Ocean greatly surpass in bulk the species that frequent the Rivers. The largest 
of the latter do not exhibit JIamraaiia which can be compared in any degree with the 
Slorse and the Basque Wialc. 
Thus, whether we investigate the Land or the Sea, every where we perceive that 
the dimensions of the Mammalia arc proportioned to the magnitude of the regions 
which they are destined to inhabit. If the Southern hemisphere bo compared, as a 
whole, with the Northern, omitting Africa and those islands which are traversed by 
the Equator, as the animals must he nearly the same on both sides of this line, we 
shall find that the Southern hemisphere will contain Slammalia whose size is gene- 
rally less than that of the corresponding animals in the North. This is, however, 
only a particular case of that more general law already explained, for the Southern 
hemisphere contains at most only small continents or large islands. 
Differences of latitude and climate lead to many important corresponding differences 
in the sizes of animals, but these do not admit of being expressed in a general law, 
but must bo noticed in detail. It most commonly happens that genera and species 
arrive at their maximum of size in the hottest regions of the globe, and descend to 
their minimum in the coldest. There arc, however, some Mammalia, such as the 
Bears, which have their maximum in the Polar Regions, while their congeners of 
the tropics are greatly inferior in bulk and strength. But there is no instance in 
any one genus where the largest species arc found alone in temperate or moderately 
warm climates ; and the same observation is equally applicable to the several indivi- 
duals of the same species. 
It commonly happens, when individuals belonging to the same species inhabit both 
the mountains aud the valleys, that the inhabitants of the mountains will be the 
smaller of the two groups. This probably arises from exposure to cold, and a scanty 
supply of food. Here again we find that correspondence between the dimensions of 
the animals and those .active habits which a mount.ain residence demands. A heavy 
and unwieldy form would have been unsuited to the difficulties of those almost inacces- 
sible heights, where the mountain races are often compelled to gather a scanty and 
precarious subsistence. 
Among the domestic animals, indieidual variations of height happen very rarely, 
and are commonly confined within narrow limits, while, on the contrary, tho varia- 
tions in the dimensions of races are sometimes both very numerous and remarkable. 
With some domestic animals tho primitive height of the wild species is preserved, or 
it has been very slightly modified. In these instances all the races have the saffl" 
height, or differ very slightly; and whenever they are found to vary from tho height 
of the wild races, it is always to become a littlo smaller. 
There are some species of domestic animals, such as the Dog .and the Horse, 
which present some races of very large dimensions, and others, on the contrary, are 
very small. AVhen, however, the medium height of all the races is ascertained, it 
is found to differ but slightly from the height of the original type, as deduced fro"' 
measurement or from reasoning. Thus the ordinary height of those species which 
vary but slightly, as well as the medium height of all the races of those species which 
vary much, approach very nearly to the dimensions of tho height belonging to the 
primitive type. In other words, species have varied but slightly in their average 
dimensions from tho time when they were first domesticated. 
There are certain lesser variations in dimensions, which depend upon the greater 
or less care which tho individuals receive on tlie p.art of Man. Tliose species whictr 
have experienced a slight diminution, belong to such as have been generally neglected 
or badly nourished. 
The predominance of tho Male over tho Female in dimensions is much more 
general, and more strongly marked among the Mammalia than among the Birds, or 
in any other class. There is a remarkable disproportion between the size of the 
Bull and that of the Cow ; of the Ram and tho Ewe ; and of the He and She Goat. 
Thu superiority of volume is not, however, essential to the male sex ; and far fr"^ 
