INSECTS 261 



the females, and these males fight with one another with their 

 mandibles. Here, therefore, the required mechanical stimulus 

 is present to account for the greater development. In the 

 social bees there are three forms the perfect fertile females, 

 the perfect males, and the workers which are permanently 

 immature females, i.e. adults in which the sexual organs 

 are imperfectly developed. The perfect females of solitary 

 bees usually possess organs specially adapted for food-collect- 

 ing, which are absent in the males. There is no difficulty in 

 accounting for this structure as the result of stimulations 

 caused by the act of carrying the pollen. A few words of 

 explanation concerning the mode in which I believe such 

 stimulation acts in insects are here necessary. So far as my 

 knowledge goes, the perfect insect does not change its form, 

 or exhibit new growths after its emergence from the pupa. 

 Nevertheless, mechanical irritations applied to a particular 

 spot on the cuticle can affect the growth of the living cells 

 beneath it, and such stimulation may show itself in the imago 

 of the next generation in a changed form of the epidermis 

 and of the cuticle produced from it. I conceive the process 

 to be of the same kind as that which produces an outgrowth 

 of the epidermis and cuticle in Crustacea, for example the 

 outgrowth of the penultimate joint of the pincher claw in the 

 lobster, which I regard as due to the pressure of the last joint 

 biting against the last joint but one. 



In the hive bee the pollen-brush on the legs is wanting in 

 the queen, but present in the worker. It seems to me possible 

 to explain this on the view that the organ has disappeared in 

 the queen through disuse, and that nevertheless she transmits 

 it to her female offspring in every generation, because the 

 reduction of it in the queen is associated with the specialisa- 

 tion and increase of the reproductive organs. The latter are 

 not fully developed in the worker, which accordingly inherits 

 the earlier stage of development of the queen. 



