2 76 MANUAL OF ZOOLOGY. 



female individuals ; but there occur some striking exceptions 

 to this rule, as seen in the Social Insects. In those organised 

 communities which are formed by Bees, Ants, and Termites, 

 by far the greater number of the individuals which compose 

 the colony are either undeveloped females, or are of no fully 

 developed sex. This is the case with the workers amongst 

 Bees, and the workers and soldiers amongst Ants and Termites. 

 And these sterile individuals, or " neuters," as they are com- 

 monly called, are not necessarily all alike in structure and 

 external appearance. Amongst the Bees, all the neuters re- 

 semble one another ; but amongst Ants and Termites they are 

 often divided into " castes," which have different functions to 

 perform in the general polity, and differ from one another 

 greatly in their characters. 



In all the above-mentioned insects the males are relieved 

 from the performance of any of the duties of life except that of 

 propagating the species ; and the females which are generally 

 solitary in each community fulfil no other function save that 

 of laying eggs. All the other duties which are necessary for 

 the existence of the community are performed by the workers, 

 or neuters. 



The organs of the two sexes are in no case united in the 

 same individual, or, in other words, there are no hermaphro- 

 dite insects. (In some very abnormal cases amongst Bees 

 hermaphrodite individuals have been observed.) As has been 

 noticed, however, before, asexual reproduction is by no means 

 unknown amongst the Insecta, and the attendant phenomena 

 are often of extreme interest. (See Introduction.) 



The great majority of insects, during their adult condition, 

 are terrestrial or aerial in their habits, but in many cases, even 

 of these, the larvae are aquatic. Many other insects live 

 habitually during all stages of their existence in fresh water. 

 A few insects inhabit salt water (either the sea itself or inland 

 salt waters) during the whole or a portion of their existence. 

 (This is the case with two or three Beetles of the families 

 Hydrophilidce. and Dytiscida, some Hemipterous Insects, and 

 the larvae of various Dipteral) Lastly, many insects live 

 parasitically upon the bodies of Birds of Mammals, or upon 

 other Insects. 



