756 CLASS IV. INSECTA. 



sexual and parthenogenetic reproduction. The result of par- 

 thenogenetic development is usually a male, but not unfrequently 

 females only arise, and in some cases both sexes arise partheno- 



R, 



FIG. 487. The viscera in the abdomen of the queen bee (after R. Leuckart). D alimen- 

 tary canal ; R rectum with rectal glands and anus ; Gk chain of ganglia ; Ov ovary ; 

 Re receptaculum seminis ; Gb reservoir of poison gland ; St sting. 



genetically from the same brood (sawflies). The queen bee 

 when fertilized stores the spermatozoa in a receptaculum seminis 

 which she can open at will, and the view is generally held that 

 if she closes this sac the unfertilized eggs then laid develop 

 into males or drones, but that if she permit the access of 

 spermatozoa to the eggs, females or workers arise. 



Polymorphism is also a dominant feature in many of the 

 colonial forms. Different castes are present, such as the worker, 

 the drone, the soldier, the queen, and so on, and it is thought 

 that these various castes are evoked by differences in the quality 

 and amount of the food supplied to the larvae.* 



The Hymenoptera form a very large order with some 30,000 

 described species. This figure will probably be multiplied by 

 eight before the existing species are exhausted. They are 

 divided into two sub-orders, the Sessiliventres and the Petiolata, 



Sub-order 1. SESSILI VENIRES, f 



Base of abdomen as broad as base of thorax or nearly so ; no waist ; first 

 abdominal segment not completely fused with thorax ; trochanter divided into 



* There is unfortunately no space in this volume to devote to the 

 fascinating habits and life histories of most of the Hymenoptera, but for 

 graphic accounts of these the student is referred to Mr. Sharp's volumes in 

 the Cambridge Natural History, and to the works of the eminent French 

 naturalist, J. H. Fabre. 



t P. Cameron, Monograph Brit. Phytophagous Hymenoptera, Ray Society,. 

 1882-1893. 



