ASPECTS OF KINETIC EVOLUTION m 



European Helix hortensis, afford the best examples of this type of 

 intraspecific diversity. The quail, or Virginia partridge, a non- 

 migratory bird widely distributed through eastern North America 

 from New England to Guatamala, shows many local subspecies 

 connected by series of imperceptible gradations. The sugar 

 maple of eastern North America has several geographical sub- 

 species. 



Stenic Species. — Species consisting of stens, that is, of nar- 

 rowly segregated subspecies, domesticated varieties, or breeds, 

 propagated by sexual reproduction. 



As a result of propagation by narrow breeding, the individual 

 members of a sten are much more nearly uniform than those of 

 normal symbasic species, or even than those of geographical 

 subspecies. As purely stenic species may be mentioned those 

 which do not exist any longer in the wild state, but are made 

 up of many local domesticated varieties. The domesticated 

 animals fall here, except as they may represent hybrids of dif- 

 ferent wild species. Of domesticated plants the Indian corn or 

 maize is the best example, since it has retained a complete system 

 of cross-fertilization, which many domesticated plants have lost. 



Very small, closely localized natural species, like the remark- 

 able Hawaiian land-snails upon which Gulick has based his 

 theory of evolution by isolation, represent essentially the same 

 condition of restricted descent as domesticated stenic varieties. 



Linic Species. — Species composed of separate, parallel or 

 slightly diverging lines of descent, propagated by autogamy or 

 parthenogenesis, and not united into a network. 



Wheat and barley are perhaps the most conspicuous examples 

 of linic species among domesticated plants, though many other 

 species are autogamous, with more or less consistencv- Strict 

 line breeding is not possible, of course, among the sexually 

 differentiated higher animals, but is sometimes approached by 

 what is called in-and-in breeding of closely related individuals. 



Line-bred organisms are extremely uniform, even more so 

 than stens. Self-fertilization involves only the combination 

 of gametes of the same origin and probably of very nearly 

 identical nuclear configuration ; at least there is even less varia- 

 tion. Linic species occur in nature as in the well-known in- 



