176 THE WALKS ABROAD OF 



or rather animals of transition. Frogs, toads, and 

 salamanders undergo metamorphoses, something like 

 insects, and serpents change their skins in a similar 

 way to the Crustacea. 



" By the conformation of their legs and of their 

 skeleton, the Batrachians, the Saurians, and the Tor- 

 toises approach the mammalia, while the cloaca of the 

 intestine, and their mode of reproduction by eggs, are 

 points of relationship with hirds. On the other hand, 

 serpents and eels (members of the fish tribe) have an 

 air of resemblance or kindred that cannot be ignored. 

 By the way," added Leon, who had become quite 

 wide-awake, " do you know which of the reptiles it is 

 that anatomically most resembles a bird ? " 



" No." 



" Well, it is the tortoise : the mandibles, the conso- 

 lidated breastbones " * 



" A bird and a tortoise ! What a pair of anatomical 

 relatives ! However much the sternum may be 

 soldered, I shall wait to admit the resemblance until 

 chickens have teeth." 



" At present they have not teeth," said the doctor ; 

 " but they have had them ; certainly not chickens 

 exactly, but some fossil birds discovered a few years 

 ago by the American geologists. And it may be 

 mentioned as a coincidence that tortoises with teeth 



The breast or plastron of the tortoise is not now considered homologous 

 with the breastbone of birds. 



