No. 570] 



SPECIES-BUILDING 



325 



for this sex-limited character. Her daughters are white 

 or colored (yellow or orange, as the case may be) in equal 

 numbers. Still another interesting heterozygous feature, 

 though uot of 11 specific " grade, was seen last summer in 

 a pure strain of Colias eurytheme. A female appeared 

 that could not upon stimulation coil up her tongue. 

 Mated with a normal male, this abnormality was in- 

 herited in various degrees by half her offspring (37 

 uncoiled and 28 coiled). One of her daughters, abnormal 

 in this respect and mated with a normal of a different 

 strain, transmitted the abnormality to about 16 per cent, 

 of her offspring (29:151), showing that the possessor of 

 this abnormality is regularly heterozygous in respect 

 to it. 



Whether (Enothera lamarckiana is or is not a complex 

 hybrid produced from two American species, is it not 

 certain that, like other wild and cultivated stock, it does 

 possess characters for which it is heterozygous, and that 

 the watcher for mutants frequently seizes upon rare com- 

 binations of recessive features as a part of his elementary 

 species? 



But to breed true is only a secondary criterion of spe- 

 cies. Inbred strains of domestic animals and plants do 

 that to a certain degree. Varieties and races to a certain 

 extent may do the same. The real criterion (and the one 

 least often practically used by the systematist) is fertility 

 within the group and sterility with other closely related 

 groups. Here dogma holds sway among writers on or- 

 ganic evolution as well as among systematists, for we are 

 told by those who have been accustomed since childhood 

 to the idea of the objective reality of species that hybridi- 

 zation of species, that is, genuine species in good and 

 regular standing before the scientific public, has played 

 very little part in the origin of new species. This atti- 

 tude was entirely logical in view of the accepted ultimate 

 definition of a species. If the individuals of one species 

 are actually sterile with members of another, hybridiza- 



