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 TZ%rolites 
above its proper range, but it turned out to be the 
young of a Zrachyceras that persisted unusually long in 
the Zvrolites 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 
