480 ORIGIN OP SPECIES 



genus, and of allied genera, often, resemble each other in 

 their immature plumage; as we see in the spotted feathers 

 in the young of the thrush group. In the cat tribe, most 

 of the species when adult are striped or spotted in lines ; and 

 stripes or spots can be plainly distinguished in the whelp of 

 the lion and the puma. We occasionally though rarely see 

 something of the same kind in plants; thus the first leaves 

 of the ulex or furze, and the first leaves of the phyllodineous 

 acacias, are pinnate or divided like the ordinary leaves of the 

 leguminosse. 



The points of structure, in which the embryos of widely 

 different animals within the same class resemble each other, 

 often have no direct relation to their condition 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 any 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 larvae of some insects 

 belonging to very dift'erent orders, and on the dissimilarity 

 of the larvae of other insects within the same order, accord- 

 ing to their habits of life. Owing to such adaptations, the 

 similarity of the larvae of allied animals is sometimes greatly 

 obscured ; especially when there is a division of labour during 

 the different stages of development, as when the same larva 

 has during one stage to search for food, and during another 

 stage has to search for a place of attachment. Cases can 



