Class 3. Inseda. 245 



fig ; the male never leaves the fruit in wMcli it has passed its early existence, and 

 in consequence of this is clumsy and apterous, whilst the female must seek for 

 young figs in which to deposit the eggs, and is active and winged. 



Fig. 209. Blastophaga grossorum. A ? (V')- B $ (\')- — After P. Mayer. 



Many species of Insects are remarkable, in that a large number of 

 individuals remain sterile throughout life, and thus take no part in 

 the propagation of the species ; these individuals possess, as a rule, 

 distinct rudiments of sexual organs, which, however, never develop 

 far enough to form fertile genital products (or they are deficient in 

 some other way, so that the individuals cannot take any part in 

 reproduction) ; such sterile individuals are always, in some Insects 

 (Bees and Ants), incompletely developed females ; in others (Termites), 

 both males and females. The occurrence of such sterile individuals 

 depends upon the fact that these Insects are social, and form larger or 

 smaller colonies; it is an expression of a division of labour within 

 the colonies, the care of the brood, etc., being relegated to the sterile 

 individuals, whilst the reproductive faculty is exercised by relatively 

 few, which, however, produce an enormous number of oSspring (c/., 

 the division of labour in Hydroid colonies) . 



Parthenogenesis has been shown to occur in many Insects. 

 In many cases, it is an exceptional occurrence ; the female of the 

 silkworm moth for instance {Bombyx mori), if unfertilised, can still 

 lay eggs, most of which atrophy, though they may develop in the 

 usual way. The same thing is knovioi for many other Lepidoptera. 

 In other cases, parthenogenesis is of more regular occurrence ; 

 in some Insects it is the rule, males appearing only occasionally; 

 so in certain Lepidoptera, e.g., Psyche helix, in which the female is 

 apterous and maggot-like, whilst the male is normal in form : or 

 the males may appear with the females, but in small numbers, and 

 apparently without, as a rule, copulating, as in Cynips rosce, a well- 

 known rose G-all-fly : or, as in some of the Saw-flies and G-all-flies, 

 reproduction is apparently exclusively parthenogenetic, in which 

 case the species consists entirely of females ; or in certain generations 

 only, reproduction may be exclusively parthenogenetic. Another 



