2S6 MANUAL OF ZOOLOGY. 



quiescent, unless touched or otherwise irritated ; is incapable of 

 changing its place; and is often attached to some foreign object. 

 This constitutes what — in the case of the Lepidoptera — is gene- 

 rally known as the " chrysalis," or '' aurelia " (fig. 93). The 

 body of the pupa is usually covered by a chitinous pellicle, 

 which closely invests the animal. In some cases {e.g., in many 

 Dipterous insects) no traces can be detected in the pupa of the 

 future insect ; but in the Lepidoptera the thorax and abdomen 

 are distinctly recognisable in the pupae; whilst in others {e.g., 

 Hymenopterd) the parts of the pupa are merely covered by a 

 membrane and are quite distinct. In some cases the pupa is 

 further protected within the dried skin of the larva ; and in 

 other cases the larva — ^immediately before entering upon the 

 pupa-stage — spins, by means of special organs for the purpose, 

 a protective case, which surrounds the chrysalis, and is termed 

 the " cocoon." 



Having remained for a variable time in the quiescent pupa- 

 stage, and having undergone the necessary development, the 

 insect now frees itself from the envelope which obscured it, 

 and appears as the perfect adult, or " imago," characterised by 

 the possession of wings. ■>■ 



Sexes of Insects. — The great majority of Insects, as is the 

 case with most of the higher animals, consist of male and 

 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 am.ongst 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 gene- 

 rally 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 



