ANNULQSA: INSECTA. 343 



thorax and abdomen are distinctly recognisable in the pupae ; 

 whilst in others (e.g., Hymenoptera) 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 amongst Ants and Ter- 

 mites. And, these sterile individuals, or " neuters," as they are 

 commonly 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 character. 



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

 same individual, or, in other words, there are no hermaphrodite 

 insects. (In some abnormal cases amongst Bees, Lepidoptera, 

 &c., 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.) 

 DISTRIBUTION IN SPACE. The great majority of Insects, dur- 

 ing 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 Hydrophilida and Dytiscidce^ some Hemipterous 

 Insects, and the larvae of various Diptera.) Lastly, many in- 



