VARIATION 



383 



individual variation within the species. Sometimes certain 

 types of variation occur so constantly that the species may be 

 subdivided into varieties. This is especially true where a 

 species is widely distributed and thus lives under difYerent 

 conditions in the various districts it inhabits. Where there 

 is variation corresponding to geographical distribution it is 

 called a geographical variety. A good example of this is 

 Lycaena pseudargiolus, the common small blue butterfly, which 

 ranges from New England to Arizona. The New England, 



Fig. 241. — Two flower heads of Gaillardia. The head on the right is the nor- 

 mal type, with ray flowers ligulate. The head on the left is a variation (sport) 

 which frequently occurs. The ray flowers in this are tubular and often quite 

 regular. X2/3. 



Middle, Southern and Southwestern States varieties of this 

 butterfly dift'er so much that they might well be classed as four 

 distinct species, were it not for the intergrading forms found 

 in the transition regions. Nor is this an isolated example. 

 Extended study of a species almost invariably widens the range 

 of its recognized variability, and sharply defined species are the 

 exception rather than the rule. 



782. Opposed to the tendency to vary is a tendency for the 

 species to maintain its character. This is evident in the re- 

 semblance of the offspring to the parents. Although the in- 



