bfeVELOPMENT OP SEX IN SOCIAL INSECTS. BB 



are fertile females (queens), sterile females (workers), and males 

 (drones). Assuming that the primary constituents for the characters 

 of both sexes are included in the same egg, Weismann considers that 

 " in many instances it appears that a stimulus decides as to which 

 group of them shall undergo development — whether the male or 

 the female." 



It is generally accepted, on the strength of the experiments of 

 Siebold and Leuckart, that in bees and wasps fertilised eggs develop 

 into females, whilst unfertilised eggs develop into males. No real 

 explanation has, I believe, hitherto been given as to how this occurs ; 

 Weismann, however, accepts the fact, and points out its utility, in- 

 asmuch as the queen can produce male or female offspring according 

 to necessity ; he then goes on to say " we can understand why the sex 

 has here been made to depend on an external impulse," although he 

 strongly disagrees with the conclusions that the " stimulus is the efficient 

 cause of the male or female character of the embryo," and warns his 

 readers against mistaking in other less apparent cases the stimulus, for 

 the causa e^Jiciens of the development, illustrating his contention by 

 the consideration of the neuters or workers of state-forming insects — 

 bees, ants and termites — ^which (workers), as well as the males and 

 females, originate from one kind of egg, the non-fertilisation determin- 

 ing the production of the male, a bountiful supply of nutritious food 

 or the reverse, giving rise respectively to the development of a queen 

 or a worker from a fertilised egg. 



The essential difference between the queens and workers is the 

 fertility of the former, the sterility (more or less absolute) of the latter. 

 It has generally been assumed that the quality of the food is the direct 

 cause of the difference, but although the bees have it in their power by 

 means of food-supply to cause a larva to become either a queen or a 

 worker, yet Weismann does not look upon the poor feeding as the real 

 causa efficiens in producing sterility in the latter, but merely as " the 

 stimulus which not only results in the formation of rudimentary ovaries, 

 but at the same time calls forth all the other distinctive characters of 

 the workers." He considers it, therefore, doubly incorrect to look 

 upon the poor nourishment as the cause of the sterility, (1) because it 

 confuses the stimulus with the real cause, (2) because it fails to 

 distinguish between an organ that has become rudimentary and one 

 imperfectly developed. Weismann's contention that the ovaries of the 

 workers "are actually rudimentary," and not simply imperfectly 

 developed is, in spite of the reiteration, difficult to understand, con- 

 sidering that the workers do sometimes lay eggs. It seems to be im- 

 perfect development all round — the number of egg-tubes are reduced from 

 about 200 (in the queen bee) to from two to six (in the worker), and it is 

 quite beside the question to say that " no matter how rich the food may 

 be, no more egg-tubes can be formed in the imaginal state." One 

 knows that structures in insects do not grow or become developed 

 when they have reached the imaginal condition ; already formed 

 structures may, in some instances, become matured, but to suppose 

 that rich nourishment in the imago stage can increase the number of 

 egg-tubes, or otherwise that we must consider the ovaries rudimentary 

 and not imperfectly developed, seems illogical and unreasonable. The 

 proof that certain fly-maggots (Musca vomitorta), sparingly fed, pro- 

 duced an abundance of eggs, and the conclusion that " in spite of the 



