258 TOWARDS THE HUMAN FORM 



instincts is in itself an unexpected argument in favour of the 

 theory of evolution, and of the mutability of living forms. 



Contemporary with this development of Insects, such small 

 creatures, the evolution of the terrestrial Vertebrates took a 

 sudden step forward. During the Triassic Period the Stego- 

 cephalan Batrachians were still represented by temnospondylous 1 

 and stereospondylous 2 forms. Among the latter, the Mastodon- 

 saurus of the Trias of Germany and England attained a gigantic 

 size ; the skull alone was one metre long. The last representa- 

 tives of this group, which did not survive the Trias, appears 

 to have been Labyrinthodon of the county of Warwick and 

 its vSouth African counterpart Rhytidosteus. Thenceforward, 

 the forms which were to persist came closer to those of to-day. 

 A small Batrachian something like a salamander, Hyolceo- 

 batrachus, is found in the Wealden clay. The anurous Batra- 

 chians began to appear in the Jurassic with Palceobatrachus, 

 but the large Batrachians, such as the more or less armoured 

 species, had had their day. The world was to belong to the true 

 Reptiles whose skin was so dry as to become scaly and in 

 whom the skull was articulated with the vertebral column by 

 a single condyle, whose branchial arches were atrophied before 

 birth without ever being used, so that the animal could breathe 

 only in the open air. 



At the time of their appearance the world was empty of large 

 animals. Vast horizons were opened to their activity. We 

 can hardly admit that the struggle for existence or natural 

 selection played any considerable part in the evolution of 

 those that did exist. This evolution was in two directions. 

 The first large Reptilian fauna that appeared on earth is known 

 to-day chiefly by the fossils found at Elgin in Scotland, in the 

 Permian of Bohemia, Thuringia, and Autun, in the Karroo 

 formations of South Africa belonging to the early part of the 

 Triassic Period, and in the North American deposits of the 

 same age. These Reptiles seem to have disappeared toward 

 the middle of this period. We have no precise indication of 

 their origin, but they appear, however, to approximate to the 

 Stegocephalan Batrachians. Pareiasaurus, which appeared, 

 as we have seen, towards the close of the Carboniferous Period, 



1 Eupelor, Brachiops, and in India, Gondwanasaurus. 



2 Trematosaurus, Capitosaurus, Metopias in the Trias of Germany ; 

 Diadetognathus, Pachygonia, Gonioglyptus. 



