We occasionally, though rarely, see something of the same kind in plants; thus the first leaves of the ulex or furze, and the first leaves of the phyllodineous acacias, are pinnate or divided like the ordinary leaves of the leguminosae.
The points of structure, in which the embryos of widely different animals within the same class resemble each other, often have no direct relation to their conditions of existence.

We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar loop-like courses of the arteries near the branchial slits are related to similar conditions--in the young mammal which is nourished in the womb of its mother, in the egg of the bird which is hatched in a nest, and in the spawn of a frog under water.

We have no more reason to believe in such a relation than we have to believe that the similar bones in the hand of a man, wing of a bat, and fin of a porpoise, are related to similar conditions of life.

No one supposes that the stripes on the whelp of a lion, or the spots on the young blackbird, are of any use to these animals.
The case, however, is different when an animal, during any part of its embryonic career, is active, and has to provide for itself.

The period of activity may come on earlier or later in life; but whenever it comes on, the adaptation of the larva to its conditions of life is just as perfect and as beautiful as in the adult animal.