122 THE EVOLUTION OF MAN. 



and the Amphibians, were doubtless in many respects 

 different from their three direct descendants of the present 

 time, but in the most essential characters they must have 

 coincided Avith the latter. Unfortunately, the germ-history 

 of the three surviv^ing Mud -fishes is as yet entirely un- 

 known; probably at some future time it will afibrd U3 

 further important information as to the tribal history of the 

 lower Vertebrates and so of our ancestors. 



Yery important information of this kind has been 

 supplied by the next Vertebrate class, that of the Batra- 

 chians (Aonphihia), which is directly connected with the 

 Dipneusta, from which it originated. To this class belong 

 the Axolotl, Salamanders (Plate XIII.), Toads, and Frogs. 

 Formerly, after the example of Linnseus, all Reptiles (Lizards, 

 Snakes, Crocodiles, and Tortoises) were also classed among 

 Amphibia. But these animals are of a far higher organiza- 

 tion, and in the most important characters of their ana- 

 tomical structure are more nearly allied to Birds than to 

 Amphibians. The true Amphibia, on the other hand, are 

 more nearly allied to the Double-breathers and to Primitive 

 Fishes : they are also much older than Reptiles. Even as 

 early as the Carboniferous Period numerous very highly 

 developed Amphibia (some of large size) were extant, whereas 

 the earliest Reptiles first appear only towards the close of 

 the Permian Period. In aU probability the Amphibia were 

 developed from Double-breathers at an even earlier period — 

 during the Devonian Period. The extinct Amphibia, of 

 which fossil remains have been preserved from that most 

 ancient Primaeval Epoch — and these are especially numerous 

 in the Trias — were distinguished by a large bony coat of mail 

 overlying the skin (like that of the Crocodile), while most 



