eye-stalks can be identified with those of the legs and jaws.

But whither does all this tend? To the very remarkable conclusion that
a unity of plan, of the same kind as that discoverable in the tail or
abdomen of the lobster, pervades the whole organization of its
skeleton, so that I can return to the diagram representing any one of
the rings of the tail, which I drew upon the board, and by adding a
third division to each appendage, I can use it as a sort of scheme or
plan of any ring of the body. I can give names to all the parts of
that figure, and then if I take any segment of the body of the lobster,
I can point out to you exactly, what modification the general plan has
undergone in that particular segment; what part has remained movable,
and what has become fixed to another; what has been excessively
developed and metamorphosed and what has been suppressed.

But I imagine I hear the question, How is all this to be tested? No
doubt it is a pretty and ingenious way of looking at the structure of
any animal; but is it anything more? Does Nature acknowledge, in any
deeper way, this unity of plan we seem to trace?

The objection suggested by these questions is a very valid and important
one, and morphology was in an unsound state so long as it rested upon
the mere perception of the analogies which obtain between fully formed
parts. The unchecked ingenuity of speculative anatomists proved itself
fully competent to spin any number of contradictory hypotheses out of
the same facts, and endless morphological dreams threatened to supplant
scientific theory.

Happily, however, there is a criterion of morphological truth, and a
sure test of all homologies. Our lobster has not always been what we