WEISMANN'S THEORY OF HEREDITY 53 



perature or food supply. The gall insects of oak and willow 

 trees have summer and winter generations very different in 

 character. The summer generation usually feeds upon the 

 soft tissues of the growing leaf and produces winged adults of 

 both sexes; whereas the winter generation feeding on the 

 woody tissues produced by a stem or metamorphosed bud, 

 may consist of wingless females only, which lay unfertilized, 

 i. e., parthenogenetic eggs. In such cases Weismann sup- 

 poses that alternative sets of determiners exist in the germ- 

 plasm, which are activated by summer or by winter condi- 

 tions respectively. 



The case of the social insects (bees and ants) is still more 

 complicated ; here there may exist four or ^ve different adult 

 forms as drones (males) queens (egg-laying females) and 

 workers or soldiers of various sorts. The workers and soldiers 

 are all imperfectly developed females, not producing eggs 

 ordinarily but merely taking care of the rest of the colony. 

 Experiment has shown that the same egg, in the case of the 

 honeybee, may produce either a queen or a worker, depend- 

 ing upon the amount and quality of the food suppHed to the 

 developing larva. The same is undoubtedly true of the 

 various sorts of soldiers, among other social insects, these be- 

 ing alternative forms of the female. Weismann supposes 

 that there are as many distinct sets of determiners in the egg 

 as there are different forms into which it may develop. This 

 line of explanation assigns to determiners located within the 

 nucleus of the egg, influences which demonstrably lie outside 

 the egg. As an explanation of polymorphism the theory of 

 alternative nuclear determiners is not only superfluous but 

 also positively erroneous. 



4. Variation. Weismann supposed that all variations 

 originate in the germ-plasm, and subsequently find expres- 

 sion in the body of the offspring, reversing the idea of La- 

 marck and Darwin, who supposed that variations first origi- 

 nate in the body and are thence transferred to the germ-cells. 

 To account for adaptive variation, Weismann framed two 

 supplementary hypotheses. 1. To account for the origin of 



