234 FOOT-NOTES TO EVOLUTION. 



tologists have not approached their work from the 

 biologic side, and biologists have been equally neglect- 

 ful of the results attained by paleontology. A distin- 

 guished zoologist once said to the writer, on being shown 

 an ontogenetic series of ammonites, and the conclusions 

 reached, " It is all beautiful, but almost too good to be 

 true." In paleontology it is especially true that a natu- 

 ralist may be a specialist in the fauna of one age, and 

 know little of that of another. Hence the animals of 

 various periods have been classified according to vary- 

 ing standards, all artificial. The only cure for these 

 discrepancies is study of ontogeny, and comparison 

 of stages of growth of the individual with ancestral 

 genera. This will also prevent the description of sup- 

 posedly new genera and species based on immature 

 specimens, as has so often been done. The writer re- 

 members once collecting numerous Ceratites in the Kar- 

 nic limestone of the California Trias, much to his aston- 

 ishment, for they ought not to occur so high up. He 

 afterward found, however, that they were not adults, 

 but adolescent ceratitic stages of Arpadites ; a similar 

 case was the finding in the same horizon a Tirolites 

 above its proper range, but it turned out to be the 

 young of a Trachyceras that persisted unusually long in 

 the Tirolites stage. At that time there was nothing in 

 the description of these genera or any of their species 

 to guide one, and so their ontogeny had to be worked 

 out independently. But there is nothing in the descrip- 

 tion of almost any fossil genera and species to prevent 

 just such mistakes, and they are constantly being made. 

 By careful study of ontogeny in comparison with 

 phylogeny the paleontologist can correlate correctly 

 fossil beds where even all the genera and species are 

 new; he can even prophesy concerning the occurrence 

 of unknown genera in certain horizons when he finds 



