270 HABIT AND INTELLIGENCE. [cHAP. 



larval stage of development. For instance, the Batra- 

 Batra- chians are, I believe, descended from an ancestor resem- 

 bling a tadpole, which, from causes that I intend to speak of 

 in a future chapter, was transformed into an air-breathing- 

 animal;^ and in every successive generation the same 

 change takes place, and at about the same age at which 

 it took place in the original ancestor. But in the 

 Land sala- land Salamander the change into an air-breather is in- 

 herited, not at the corresponding age, but at birth ; and 

 thus it undergoes no metamorphosis. This account of the 

 matter is, I think, in accordance with what we know of 

 the laws of habit and variation, and of the facts of 

 embryology. 



It is desirable, whenever it is possible, to adopt Darwin's 

 plan of reasoning from relations between varieties, the com- 

 mon origin of which is known, to relations between species, 

 the common origin of which can only be inferred ; and 

 Darwin has stated an instance in which the variations that 

 mark the several varieties of one species mostly appear some 

 time after birth, but in one variety are very conspicuous 

 Youug at birth. " The young of the short-faced tumbler differs 

 vM-ious ° fi'*^'^ ^^6 young of the wild rock-pigeon and of the other 

 breeds. breeds in all its proportions, almost exactly as much as in 

 the adult state ;" while the young of the other breeds of 

 the pigeon, even of those which are most unlike in the 

 adult state, are very nearly alike.^ The short-faced 

 tumbler, in presenting from the first the peculiar cha- 

 racters in which it differs from the original race of pigeons, 

 may be compared to the land salamander, which breathes 

 air from the first ; while the other varieties of pigeon, in 

 presenting at first the character of the original race, resem- 

 ble those Batrachians which commence their lives breathing- 

 water, like the fishes from which they are descended. 

 Series. To return to the subject of metamorphoses. We find in 



nature the following series : — 



1 I do not mean that this transformation took place in one generation. 

 On the contrary, I believe it must have occujiied countless generations, 

 and must have passed through many specific forms, like those preserved 

 among the Perennibranchiates. 



2 Darwin's Origin of Species, p. 626. 



