250 



ilABIT AND INTELLIGENCE. 



[chap. 



Vertebrates) into the reptile, the bird, and the mammal? 

 Of course, most of these questions cannot be answered 

 in detail. As already remarked, most of the transitional 

 forms have perished without leaving a ruin behind them. 

 But the laws of Habit are perfectly well known, and we 

 know something, though not much, of the laws of correla- 

 tion ; and with the aid of these laws it is, I believe, 

 possible so to combine and co-ordinate the facts of em- 

 bryology and comparative morphology, that in some cases, 

 though not in all, we can arrive at definite, though general, 

 conclusions as to the stages of modification through which 

 organic forms have passed, and as to the causes and laws 

 which have determined the modifications. 



How do If this chapter is read by any intelligent man un- 



thatrudi- acquainted with zoology, the question may probably occur 

 mentaiy to him, by what criterion are we able to assert that the 



organs are 

 aborted, 

 and not 

 nascent ? 



Classifica- 

 tion. 



leg-bones of serpents and the wing-bones of the apteryx 

 are proofs of descent from animals that had legs and 

 wings ? Is it not as probable a conjecture that they are 

 remnants of the races from which the animals that have 

 legs and wings are descended ? May not all birds be 

 descended from the apteryx tribe, and all air-breatliing 

 Vertebrates from the serpents ? 



There are two answers to this question. The one is 

 based on the facts of classification. Serpents are not on 

 the line of ascent from fishes to the air-breathing Verte- 

 brata. The transition is not tlirough the serpents, but 

 through the Batrachians (newts, &c.). And there is no 

 reason for thinking that the apteryx is on or near the 

 line of ascent from reptiles to birds. The ascent was, in 

 all probability, through the reptilian birds, the former 

 existence of which has been lately shown by geological 

 evidence. 



But there is another answer, even more satisfactory than 

 this, inasmuch as it is independent of comparative mor- 

 phology, and depends only on the relation of structure to 

 function in the species. A serpent can never have given 

 origin to an animal with legs, or an apteryx to a bird with 



