EMBRYOLOGY 395 



he cannot now tell whether it be that of a mamma), 

 bird, or reptile. The vermiform larvae of moths, flies, 

 beetles, etc., resemble each other much more closely 

 than do the mature insects ; but in the case of larva- . 

 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 leguminos*. 



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, 

 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 



