624 THE AMERICAN NATURALIST [Vol. LI 



from low-crowned teeth of simple pattern into long- 

 crowned teeth of a complex pattern. And even in the 

 practical absence of paleontological evidence it is suffi- 

 ciently established that the Cetacea, which are now of 

 pelagic habit and fish-like habitus, represent transformed 

 terrestrial or littoral quadrupeds, which at a remote epoch 

 were placental mammals of some sort. Nor can it be justly 

 doubted that birds are ''glorified reptiles," that bats are 

 volant derivatives of arboreal mammals, that teleosts 

 have been derived from ganoids. Detailed knowledge of 

 the evidence in hundreds of such cases leads the paleon- 

 tologist to say with considerable confidence: "this later 

 type of animal has probably been derived from that earlier 

 type ; this structure has undergone such and such changes 

 during certain geological periods." 



Professor Bateson is equally cold towards outworn 

 notions about adaptation. ''Naturalists may still be 

 found, ' ' he says,^ ' ' expounding teleological systems which 

 would have delighted Dr. Pangloss himself, but at the 

 present time few are misled. The student of genetics 

 knows that the time for the development of theory is not 

 yet. He would rather stick to the seed-pan and the in- 

 cubator." 



Two very distinct ideas seem to be implied in this pas- 

 sage and the context, first the rejection of the supposed 

 principle of progressive adaptation in evolution, and sec- 

 ondly the idea that conclusions regarding evolution should 

 be limited to those in which control experiments can be 

 made. 



As to the principle of progressive adaptation, it is an 

 indisputable fact that existing animals possess structures 

 which are highly efficient in the performance of certain 

 functions, e. g., the locomgtive apparatus of the horse, 

 effective for progression over hard ground; its masti- 

 catory apparatus, effective in the trituration of siliceous 

 vegetation. Paleontologists, after studying the phylo- 

 genetic history of such structures, must infer that pro- 

 gressive advance of structure has been influenced to a 



2 md., p. 293. 



