No. 570] SPECIES-BUILDING 323 



variations appear under uniform external conditions 

 leads one to be very skeptical toward most of the past 

 experimental work supposed to show the effects of the 

 environment upon insects in modifying the germ cells. 

 Any one wishing to try an experiment on the production 

 of variations by the influence of the environment, or upon 

 the inheritance of acquired characteristics, should deny 

 himself absolutely this privilege until he shall have bred 

 under normal conditions at least a thousand individuals 

 of the stock that he will subsequently employ. 



That species necessarily breed true to the specific char- 

 acters ascribed to them by their inventors is an unveri- 

 fied dogma. At best the reporter picks out stray individ- 

 uals here and there from a vast procession of which he 

 can only see glimpses, and, trusting to the credulity of the 

 public in the established ideas about these matters, he 

 creates upon paper a new species. Doubtless the unit 

 characters of " specific " grade in the stock of some spe- 

 cies are more generally constant or homozygous than 

 those of certain others, but it is reasonable to suppose 

 that, owing to dominance the heterozygous 2 condition re- 

 garding certain characters is frequently masked and un- 

 noticed in apparently pure strains of wild stock. If the 

 heterozygote respecting a certain character be compara- 

 tively rare, or if it be a heterozygote based on several 

 interacting factors, like redness in the kernel of Nilsson- 

 Ehle's wheat, 3 it may cross again and again with 

 the homozygous dominant, or with another heterozygote 

 of similar nature to itself, without the appearance in the 

 population of the recessive. That specific and varietal 

 characters do exist in heterozygous condition in wild 

 stock of "pure" species, unmasked by dominance and 

 easily detected, I have found to be the case in Colias at 

 several points. The color pattern as a whole apparently 

 fluctuates in variation, but these variations in detail are 



