80 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



reason, to admit Darwinian selection as the true 

 cause of the production of new forms : the survival 

 of the fittest is not the origin of the fittest. 



The variation of beings occurs in the species, 

 but also in the genus and even in the family. Cope 

 quotes numerous examples of this, both from living 

 beings and from fossil animals. Among the first he 

 dwells on the characteristics of gradual transition 

 between certain families of Batrachians by the pro- 

 gressive addition of a new characteristic, which 

 superadds itself, during the development of the 

 embryo, to the characteristics of the preceding family. 

 Thus, the lowest family of Batrachians, the Bufoni- 

 formes [toads], possess a movable scapulary girdle (or 

 embryonic sternum) and no teeth ; the next family, 

 the Arciferi, have the same scapulary girdle as the 

 toads, but have, in addition, teeth ; lastly, the family 

 of Eaniformes, or frogs, have both a fixed scapulary 

 girdle (complete sternum) and teeth. It is evident 

 that a slight improvement of the scapulary girdle 

 would transform an Arcifer into a Ranif orm ; the 

 appearance of teeth in a Bufoniform would make 

 it an Arcifer. The changes of species, genera, or 

 families, therefore, appear not only as additions, 

 but, sometimes also as subtractions of character- 

 istics in the embryogenic history of the modified 

 generation. 



The palaeontological history of the Camelidse 

 offers us another striking example of the same 

 facts. The action of geological times has operated 

 on this group, first by the progressive consolidation 

 of the bones of the foot into a single, or cannon 

 bone, and, secondly, by the reduction of the incisors 



