REPTILIA : SEYMOURIA 67 



a single large temporal vacuity and foot structure not unlike that 

 of Varanosaurus, was an animal which had diverged in other 

 respects widely from its contemporary reptiles. It had developed 

 an ectepicondylar foramen, and had become a very swift-moving 

 reptile. 



In summation: The evolution of the land vertebrates had 

 developed so far by the close of Carboniferous times that reptiles 

 of considerable diversity of habits and structure had arisen, and 

 it would be unreasonable to suppose that the temnospondyls and 

 cotylosaurs were exceptions, that they still retained their primitive 

 characters unchanged or almost unchanged; that the many resem- 

 blances between such creatures as Diadectes, Seymouria, Limnoscelis , 

 and Eryops were the result of heredity rather than adaptive 

 evolution. We have been deceived time without end, and are 

 yet often deceived in every group of animal and vegetable life by 

 resemblances which we impute to heredity — that is, to blood rela- 

 tionships — rather than to adaptations to like environmental condi- 

 tions. Of course, it will be conceded that animals whose habits 

 and environments have changed little have probably not changed 

 their structure greatly. The marsh turtles have continued for 

 millions of years with not very great modifications of their skeletal 

 structure; and I do not wish to say that all the resemblances 

 between Diadectes and Eryops, for instance, are necessarily of 

 adaptive origin, but simply that we have many more facts to learn 

 before we can say that they are of genetic origin. The most that 

 we can expect to discover in the Permian fauna are the ways in 

 which the evolution of the reptiles from the amphibians has occurred; 

 to discover archaic forms that, one by one, bridge over the class 

 differences between the amphibians and reptiles. And in this we 

 have been very successful; there is scarcely a detail in the whole 

 structure of the reptiles whose origin is yet inexplicable; dis- 

 tinguishing characters, one by one, have been completely or largely 

 broken down, but we have, nevertheless, not yet found a creature 

 about which there is doubt as to its position in the two classes 

 when fullv known. 



