vertebrate animal, he cannot now tell whether it be that of a mammal, bird,
or reptile. The vermiform larvae of moths, flies, beetles, &c., resemble
each other much more closely than do the mature insects; but in the case of
larvae, the embryos are active, and have been adapted for special lines of
life. A trace of the law of embryonic resemblance, sometimes lasts till a
rather late age: thus birds of the same genus, and of closely allied
genera, often resemble each other in their first and second plumage; as we
see in the spotted feathers in the thrush group. In the cat tribe, most of
the species are striped or spotted in lines; and stripes can be plainly
distinguished in the whelp of the lion. We occasionally though rarely see
something of this kind in plants: thus the embryonic leaves of the ulex or
furze, and the first leaves of the phyllodineous acaceas, are pinnate or
divided like the ordinary leaves of the leguminosae.

The points of structure, in which the embryos of widely different animals
of 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 course 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 same 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 will suppose that the
stripes on the whelp of a lion, or the spots on the young blackbird, {440}
are of any use to these animals, or are related to the conditions to which
they are exposed.

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. From such special adaptations, the
similarity of the larvae or active embryos of allied animals is sometimes
much obscured; and cases could be given of the larvae of two species, or of
two groups of species, differing quite as much, or even more, from each
other than do their adult