Teachings of Thomas Huxt.ey 17 



the work of destructive agencies in nature, such, 

 as rains, winds, and frost have obliterated many 

 evidences of former types and therefore have 

 made the geological record imperfect; yet foot- 

 prints of these former types may frequently 

 be seen in the rocks, which do not conform to 

 the footprints of any known species ; hence we 

 may be allowed to assume that they belonged to 

 the obliterated variation derivatives. The doc- 

 trine of evolution is therefore not impaired by 

 this line of reasoning. 



The favorable evidence for the evolutionary 

 hypothesis is derived from representation in 

 animals of two types or forms, viz., the inter- 

 calary or intermediate, and the linear or imme- 

 diate or direct. Cuvier was the first to show 

 that paleontological research leads to the dis- 

 covery of types of animals independent in them- 

 selves, yet serving to link together other types 

 to which they bear some resemblance. The first 

 of these was the Anoplotherium which proved 

 to be allied to the pigs on the one hand, and 

 to the ruminants on the other. Another was 

 the Paleotherium which had characteristics be- 

 longing to the rhinoceros, the horse, and the 

 tapir, creatures which to all appearances were 

 entirely different and distinct. Thus gaps in 

 our existing series of mammals have been and 

 are being filled up more and more, strengthen- 

 ing the chain of phylogenetic progress. 



Linear or direct types are best represented 



