44 HISTORY OF THE HUMAN BODY 



trend of opinion leads to the rejection of the four living an- 

 thropoids (gorilla, chimpanzee, orang and gibbon) as direct 

 ancestral forms. Owing to the modifications time is apt to 

 produce in animal species it seems more logical to expect to 

 find the connection in some extinct type, as, for example, the 

 European Dryopithecus of the middle Miocene. As the case 

 stands at present, however, there are few animal species con- 

 cerning which so many of the intermediate links have been 

 preserved as in the case of man, and to the scientist the 

 " missing-links," the discovery of which would be of the 

 greatest importance, are not those representing intermediate 

 anthropoidal forms, but those lying in the far greater gaps 

 lower down, as, for example, between lemurs and primitive 

 insectivores, or between the Pantotheria and the theromorphs, 

 which would throw further light upon the reptilio-amphibian 

 ancestry of the Mammalia. 



Naturally the phylogenetic stages which lie in the direct 

 line of human ancestry are of the most value as historical 

 records, and as such form the main subject of study for the 

 morphologist, but collateral lines furnish many helpful sug- 

 gestions, and in cases where a group of animals which repre- 

 sents an ancestral line has become wholly extinct, dependence 

 must be placed upon the nearest related group, although not 

 directly in the line of descent. With this in mind it will be 

 seen from the foregoing that the phylogenetic stages of the 

 greatest value in the present discussion are the following : 



1. Amphioxus. 



2. Cylostomes. 



3. Selachians. 



4. Ganoids. 



5. Urodeles (as a substitute for the Stegocephali). 



6. Reptiles (preferably the chelonians, as the nearest living 



allies of the theromorphs). 



7. Monotr ernes (the nearest living allies of the Pantotheria). 



8. Marsupials (probably not very near the direct line, but 



suggestive of the conditions in the primitive Insec- 

 tivora). 



