VARIATIONS IN ANIMALS AND PLANTS 495 



the characters of a species are not those which appear, but the ability 

 to develop these characters under the conditions surrounding the 

 ancestry of the individual. 



But there is no evidence that the direct influence of environment is 

 a factor in the separation of species, except as its results may be acted 

 upon by natural selection. We have no reason to suppose that the 

 environment of one generation determines the heredity of the next. 

 It is true in a broad way that the ill-nourished offspring has weaker or 

 less numerous offspring, but weak or strong, their hereditary traits 

 are those of their actual parent stock. 



The features of the ' ontogenetic species ' or subspecies, have long 

 been known under the name of ' convergence of characters,' ' parallel- 

 ism ' and ' analogous variation.' An ' ontogenetic species ' is a group 

 in which the likeness among the members is due, not to genetic con- 

 nection, but to the exposure of the individuals to like conditions of 

 development. Hence it should have no recognition in taxonomy, which 

 deals with phylogenetic species and subspecies only. But no species 

 is truly defined when only the usual characters, those developed under 

 usual conditions, are considered. To know the species fully, we should 

 know what qualities individuals may develop under all the varied rela- 

 tions of the environment in which they may be placed. 



Ontogenetic species, however, tend to become phylogenetic, in isola- 

 tion from the rest of their kind, by interbreeding among themselves, 

 and under new conditions of selection. The real characters of the 

 race thus formed may be wholly obscured by the more evident char- 

 acters due to food conditions or to reaction from the environment. 

 To test the characters, phylogenetic and ontogenetic, and to purge the 

 system of species and subspecies founded on the latter, will be part of 

 the work of the student of species for a long time to come. 



Taking concrete illustrations — the Loch Leven trout, Salmo leven- 

 ensis, recently discussed, is distinguished in its native waters by certain 

 obvious characters. These disappear when the eggs are planted in 

 brooks in England or in California, and the species develops as the 

 common English brook trout. But it is conceivable that the obvious 

 or ontogenetic traits of the Loch Leven trout are not the real or phylo- 

 genetic distinctions, and that the latter, more subtle, engendered 

 through individual variation, inheritance, selection and isolation, really 

 exist, although they have escaped the attention of ichthyologists. 



After the species was planted in Yosemite Park in 1896, it remained 

 for nine years unnoticed. In 1905, individuals sent to me were, so 

 far as I could see, exactly like English brook trout. But it is con- 

 ceivable that differences in food and water have caused slight onto- 

 genetic distinctions. It is certain that in isolation from all parent 

 stocks they will, in time, develop larger differences, which, after many 

 thousand generations, will be specific or subspecific. At present, these 



