STUDIES OF VARIATION IN INSECTS 329 



doubtedly an actual actively-regulative factor in species control, 

 will take care of it. 



Variation in Parthenogenetically Produced Individuals and 

 in those of Bisexual Parentage. — Among the " explanations " 

 of variation, that emphasized by Weismann is the most con- 

 spicuous. The admixture of the heredity-bearing germ-plasm 

 of two individuals explains why there is variation, and has in- 

 deed for chief raison d'etre (if " rejuvenescence " be not the 

 primary reason) the production of those variations necessary for 

 the grounding of the natural selection theory. Sex is indeed 

 for the sake of variation ; variation is the result of amphimixis. 



As a matter of fact, parthenogenetically produced animals 

 vary, and by casual inspection seem to vary in practically equal 

 degree with those of biparental ancestry. That in certain in- 

 stances they really do vary quite as much as do the progeny of 

 two parents is shown by our statistical study of the variation in 

 series of drone honey-bees (parthogenetically produced) as com- 

 pared with the variation of the same organs in series of worker 

 honey-bees, of the same maternal parentage as the drones, but 

 having an added parent, with series of workers and of entirely 

 distinct parentage. The organs examined for variation in these 

 series of bees are the wings, organs used by both drones and 

 workers and having no immediate relation either structurally 

 or physiologically to the differentiation of these two castes or 

 kinds of individuals of the honey-bee species. The workers 

 are " incomplete " only in that most of them are infertile : in no 

 other structural or physiological feature of their make-up are 

 they less " complete " than the drones. They are indeed dis- 

 tinctly the more specialized kind of individual of the two and 

 according to one of the early Darwinian canons of variation 

 might be expected on that account to vary more than the drones. 

 But the drones are males and according to another commonly 

 accepted belief, this is the explanation for a larger variation on 

 their part, if such larger variation occurs. As a matter of fact 

 it does. Reference to our account (p. 214, et seq.) shows that 

 the drones in all the series studied show markedly more varia- 

 tion in the venation of the wings (something the entomological 

 systematists expect to see little of, as witness the constant use 



