CHAP. 1.1 DEFINITION \M> STRUCTURE OF INSECTS. 15 



the protrusible penis. In the female there are generally paired 



o\aries from which tin- eggs arc discharged through the oviducts 

 into .1 common tube (tin- vagina) into which also runs the open end 

 of the spermatheca or receptacle in which the male spermatozoa 

 are received and stored. The ovipositor, which as its name implies, 

 is the instrument In winch tin- eggs are placed in position, assumes 

 very different forms in different groups, and is often 

 externally, as in in. m\ grasshoppers, Ichneumon-flies, etc.; when 

 internal it is capable 0! protrusion often to a considerable extent. 

 Besides the actual sexual organs there are also in both sexes 

 various accessory structures; in the male, for example, there is 

 frequently a complex armature of chitinous hooks and claspers 

 which often differ in character in species otherwise hardly distin- 

 guishable and which are thus of great assistance in systematic 

 work ; and in the female there may he sebific glands, such a 

 in various grasshoppers, which pour out a gummy fluid which 

 cements the eggs into a mass and at the same time gives them .1 

 protective covering. A great deal of work has been dune on the 

 spermatogenesis and oogenesis of insects but this subject cannol 

 be entered into here. 



Fertile reproduction is gcnei.dk attained in insects, as in the 

 higher animals, by the union of the two sexes but occasionally 

 aberrant forms of reproduction are met with. Of these the com- 

 monest is Agamcgenesis (a name derived from Greek words mean- 

 ing " birth without marriage"), commonly called Parthenogenesis 

 (Greek, " virgin-birth ") ; in this case the female lays fertile eggs 

 without the intervention of the male and this phenomenon is the 

 normal mode of reproduction in the case of many Aphids and is 

 also commonly met with in some other groups (scale-insects, bees, 

 and moths). 



The case of the honey-bee is well known but is of considerable 

 interest. The queen-bee has the power of withholding the passage 

 oi spermatozoa from the spermatheca in which these are stored. 

 When eggs descend from the ovary, it the queen-bee allows sper- 

 matozoa to issue, the eggs are fertilized and become females, 

 workers or queens according to the food on which the young larvae 

 are fed. If, however, exit of spermatozoa is prevented by the 

 queen-bee (or if she is old and the spermatozoa exhausted) tin- 

 unfertilized eggs only develop into males (drones). The name 

 Pedogenesis is given to cases in which agamogenetic reproduction 

 occurs in the larval stage and this is known to occur in a few 

 Diptera and Coleoptera (Miastor, Chironomus, Micromalthidc 

 minute wingless flj (Termitoxenia), commonly found in Termites' 

 mounds in India, is reputed to be hermaphroditic, combining both 



