Mr.Darwin gives us a diagram exhibiting the variation of an original species into a score or so of varieties, ending in distinct species.

But this is very far, indeed, below the necessities of the case.

The horse hair worm lays 8,000,000 of eggs; and the primeval germ, whatever it was, could hardly be less fertile, since fertility increases with simplicity of structure.
But, taking 8,000,000 to begin with, here were as many varieties; since no two of them, or of any creature, could be exactly alike.

The next generation would give 8,000,000 times as many varieties, and so on till Natural Selection began to thin off the feeble.

But here we have, instead of a few well-marked varieties, an infinite multitude of imperceptible variations, rendering classification impossible.