But there are some insects—as, for instance, the Aphides—which certainly are not among the least voracious, and which grow and breed at the same time. There are also many scavengers among other groups of animals—such, for instance, as the dog, the pig, and the vulture—which undergo no metamorphosis. It is certainly true that, as a general rule, growth and reproduction do not occur together; and it follows, almost as a necessary consequence, that in such cases the first must precede the second. But this has no immediate connection with the occurrence of metamorphoses. The question is not, why an insect does not generally begin to breed until it has ceased to grow, but why, in attaining to its perfect form, it passes through such remarkable changes; why these changes are so sudden and apparently violent; and why they are so often closed by a state of immobility—that of the chrysalis or pupa; for undoubtedly the quiescent and death-like condition of the pupa is one of the most remarkable phenomena of insect-metamorphoses. In the first place, it must be observed that many animals which differ considerably in their mature state, resemble one another more nearly when young. Thus birds of the same genus, or of closely allied genera, which, when mature, differ much in colour, are often very similarly coloured when young. The young of the lion and the puma are often striped, and the fœtal Black whale has teeth, like its ally the Sperm whale. In fact, the great majority of animals do go through well-marked metamorphoses, though in many cases they are passed through within the egg, and thus do not come within the popular ken. “La larve,” says, Quatrefages, “n’est qu’un embryon à vie indépendante.”[40] Those naturalists who accept in any form the theory of evolution, consider that “the embryonal state of each species reproduces more or less completely the form and structure of its less modified progenitors.”[41] “Each organism,” says Herbert Spencer,[42] “exhibits within a short space of time a series of changes which, when supposed to occupy a period indefinitely great, and to go on in various ways instead of one way, give us a tolerably clear conception of organic evolution in general.”