PLANT-LICE. 237 



leaves of the infested plants and blocks up their stomata. All 

 Aphides have a mealy or waxy substance on the skin which 

 repels water. Winged and wingless females occur, the males 

 being also often winged. Parthenogenetic reproduction takes 

 place ; both oviparous and viviparous females are found in aU 

 species. The wingless forms are generally asexual, and so are 

 the summer winged females. Ova are usually laid only in 

 the autumn by the oviparous female after fertilisation by 



Fig. 121. — Cherry Aphis (Myeus cerasi). 

 a. Winged 9 ; b, apterous ? . 



the male. The tarsi are two-jointed, and the wings contain 

 very few veins, by which the Dolphins, as they are called 

 in Kent, are partly classified. The reproductive powers of 

 these insects are enormous as well as peculiar. The wingless 

 female, starting in the spring, produces with great rapidity living 

 young without the agency of a male ; these asexuaUy produced 

 young or lice soon grow sufficiently to start reproducing again, 

 and so on for eight or nine generations. As a rule, a plant 

 becomes smothered by these wingless forms ; and in the summer 



