Origin of Species Variorum

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 .. 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. In how important a manner this has acted, has recently been well shown by Sir J. Lubbock in his remarks on the close similarity of the larvæ of some insects belonging to very different orders, and on the dissimilarity of the larvæ of other insects within the same order, according to their habits of life. From such adaptations, especially when they imply a division of labour during the different stages of development, as when the same larva has during one stage to search for food, and has during another stage to search for a place of attachment, the similarity of the larvæ ... of allied animals is sometimes greatly obscured; and cases could be given of the larvæ of two species, or of two groups of species, differing more from each other than do the adults. ↑ In most