366 SCOTT. [Vol. V. 



odont molars ; have lost all or nearly all of the superior incisors ; 

 have developed types of skull which, with all their differences, 

 have many features in common ; in both the limbs and especially 

 the metapodials have greatly elongated ; the ulna and fibula are 

 very much reduced and in precisely the same fashion ; the cannon- 

 bones in both series are composed of just the same elements ; in 

 both episphenial processes have been independently developed 

 upon the zygapophyses of the lumbar vertebrae, and in both the 

 odontoid process of the axis, which was originally peg-like, has 

 become spout-shaped. The stomach of the camel resembles 

 that of the typical ruminants in a way that we cannot suppose 

 to be due to a common inheritance from the Dic]iobiinid<z. In 

 both series the final result is strikingly alike, though the paral- 

 lelism is by no means complete, and as we have already noticed, 

 the keen insight of Riitimeyer detected the true relationship 

 from a comparison of the modern forms alone. In one respect, 

 however, I must venture to differ from his interpretation of the 

 facts. Riitimeyer regards the llama as less aberrant than the 

 camel ; a better statement would perhaps be that its parallelism 

 to the Pecora is more complete. 



The resemblance between the creodonts and the carnivorous 

 marsupials has been much dwelt upon, but I think that it may 

 be shown that the relationship between the two groups is a very 

 remote one and that the points of likeness are due partly to 

 parallel development and partly to the retention in both series 

 of certain primitive characteristics. 



The group of reptiles presents very similar phenomena; on 

 the one hand there are the Dinosauria, which have developed 

 so many ornithic peculiarities in the hind limb, while, on the 

 other hand, the Pterosauria possess equally striking avian feat- 

 ures in the skull, cervical vertebrae, sternum, and shoulder girdle. 

 To assume, as has been done, that the birds are diphyletic, is to 

 admit the principle of convergence in almost its extreme form, 

 while if this be denied, then the bird-like structures of either 

 the pterosaurs or the dinosaurs, or both, must be due to 

 parallelism. 



Among the invertebrates the same problems confront us. 

 Thus Wurtenberger finds well marked convergences among the 

 ammonites. " Aus den Betrachtungen welche wir bisher uber 

 die Stammesgeschichte der Ammoniten angestellt haben, diirfte 



