244 ZOOLOGY FOR MEDICAL STUDENTS chap. 



The Hymenoptera represent a very high grade of insect evolution, 

 both in their structure and in their psychical features. The latter is 

 specially apparent in those members of the group (bees, ants) which 

 live in complex social communities. Here, as in the case of the termites, 

 those types which have made a success of communal life show an intense 

 specialization of the individuals for different functions in the community. 

 Here again we see in the Bee a restriction of the reproductive function, 

 in so far at least as the female sex is concerned, to a single individual — 

 the queen. The ordinary females in the community are kept from 

 attaining sexual maturity by being fed with different food and these 

 sterile undeveloped females are the workers of the community. More 

 than one female may receive the food necessary for sexual development, 

 but in such a case the first queen that reaches the adult condition proceeds 

 to sting the others to death. This is apparently not the only way in 

 which sexual development is controlled. The males or drones are pro- 

 duced from eggs which develop by parthenogenesis, i.e. without being 

 fertilized, and it is believed that the queen, whose spermatheca has been 

 filled with spermatozoa during the first flight, is able voluntarily to 

 prevent or to allow access of the spermatozoa to the eggs as they are 

 being laid. 



In the case of the Ants the community consists of functional males 

 and females provided with wings, and wingless undeveloped females 

 which may be differentiated into ordinary workers and " soldiers." In 

 particular species various extraordinary types of specialization are 

 found. Thus in certain ants which feed on honey (Myrmecocystus, 

 etc.) some of the individuals are differentiated as honey-pots, taking 

 in surplus honey until the abdomen is swollen out into a large globe, 

 and hanging on to the roof of a special store chamber in the nest. 

 Again in Colobopsis certain of the workers have enormously swollen 

 heads which serve as animated stoppers to the galleries leading to the 

 nest. 



Among the Hymenoptera are included the Gall-flies which deposit 

 their eggs in the tissues of plants, the presence of the egg or of the 

 larva that develops from it stimulating the plant tissue to pro- 

 duce a gall or tumour having a quite definite specific appearance 

 according to the species of Gall-fly. The Ichneumon-flies deposit their 

 eggs on or in the bodies of other insects, usually the larvae of Lepi- 

 doptera, and play a great part in keeping the numbers of these insects 

 in check. 



A common feature of the Hymenoptera is that the first segment of 

 the abdomen is fused with the thorax : in many members of the group 



