Chap. XIII. 
EMBEYOLOGY. 
439 
circumstance mentioned by Agassiz, namely, that having 
forgotten to ticket the embryo of some vertebrate ani¬ 
mal, 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 occasion¬ 
ally 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 leguminosse. 
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 condi¬ 
tions 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 condi¬ 
tions of life. No one will suppose that the stripes on 
the whelp of a lion, or the spots on the young blackbird, 
