On the Study of Zoology | Page 7

crab, the water flea, and the barnacle, and separate them from all other
animals; whence they collectively constitute the larger group, or class,
'Crustacea'. But the 'Crustacea' exhibit many peculiar features in
common with insects, spiders, and centipedes, so that these are grouped
into the still larger assemblage or "province" 'Articulata'; and, finally,
the relations which these have to worms and other lower animals, are
expressed by combining the whole vast aggregate into the sub-kingdom
of 'Annulosa'.
If I had worked my way from a sponge instead of a lobster, I should
have found it associated, by like ties, with a great number of other
animals into the sub-kingdom 'Protozoa'; if I had selected a fresh-water
polype or a coral, the members of what naturalists term the
sub-kingdom 'Coelenterata', would have grouped themselves around
my type; had a snail been chosen, the inhabitants of all univalve and
bivalve, land and water, shells, the lamp shells, the squids, and the
sea-mat would have gradually linked themselves on to it as members of
the same sub-kingdom of 'Mollusca'; and finally, starting from man, I
should have been compelled to admit first, the ape, the rat, the horse,
the dog, into the same class; and then the bird, the crocodile, the turtle,
the frog, and the fish, into the same sub-kingdom of 'Vertebrata'.
And if I had followed out all these various lines of classification fully, I

should discover in the end that there was no animal, either recent or
fossil, which did not at once fall into one or other of these
sub-kingdoms. In other words, every animal is organized upon one or
other of the five, or more, plans, whose existence renders our
classification possible. And so definitely and precisely marked is the
structure of each animal, that, in the present state of our knowledge,
there is not the least evidence to prove that a form, in the slightest
degree transitional between any of the two groups 'Vertebrata',
'Annulosa', 'Mollusca', and 'Coelenterata', either exists, or has existed,
during that period of the earth's history which is recorded by the
geologist. Nevertheless, you must not for a moment suppose, because
no such transitional forms are known, that the members of the
sub-kingdoms are disconnected from, or independent of, one another.
On the contrary, in their earliest condition they are all alike, and the
primordial germs of a man, a dog, a bird, a fish, a beetle, a snail, and a
polype are, in no essential structural respects, distinguishable.
In this broad sense, it may with truth be said, that all living animals,
and all those dead creations which geology reveals, are bound together
by an all-pervading unity of organization, of the same character, though
not equal in degree, to that which enables us to discern one and the
same plan amidst the twenty different segments of a lobster's body.
Truly it has been said, that to a clear eye the smallest fact is a window
through which the Infinite may be seen.
Turning from these purely morphological considerations, let us now
examine into the manner in which the attentive study of the lobster
impels us into other lines of research.
Lobsters are found in all the European seas; but on the opposite shores
of the Atlantic and in the seas of the southern hemisphere they do not
exist. They are, however, represented in these regions by very closely
allied, but distinct forms--the 'Homarus Americanus' and the 'Homarus
Capensis': so that we may say that the European has one species of
'Homarus'; the American, another; the African, another; and thus the
remarkable facts of geographical distribution begin to dawn upon us.
Again, if we examine the contents of the earth's crust, we shall find in
the latter of those deposits, which have served as the great burying
grounds of past ages, numberless lobster-like animals, but none so
similar to our living lobster as to make zoologists sure that they

belonged even to the same genus. If we go still further back in time, we
discover, in the oldest rocks of all, the remains of animals, constructed
on the same general plan as the lobster, and belonging to the same great
group of 'Crustacea'; but for the most part totally different from the
lobster, and indeed from any other living form of crustacean; and thus
we gain a notion of that successive change of the animal population of
the globe, in past ages, which is the most striking fact revealed by
geology.
Consider, now, where our inquiries have led us. We studied our type
morphologically, when we determined its anatomy and its development,
and when comparing it, in these respects, with other animals, we made
out its place in a system of classification. If we were to examine every
animal in a similar manner, we should