pon one or other
of the five, or more, plans, the existence of which 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.[1]
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 similar, 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.

[Footnote 1: The different grouping necessitated by later knowledge does
not affect the principle of the argument.--1894.]

In this broad sense, it may with truth be said, that all living animals,
and all those dead faunae which geology reveals, are bound together by an
all-pervading unity of organisation, 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
_Homuarus_; 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 ev