THE OPEN TYPE OF WING-GROWTH 71 



grasshoppers and cockroaches, for their jaws are highly 

 modified for piercing and sucking, so that they are adapted 

 for taking not solid but liquid food. The labium is a long, 

 jointed beak, projecting beneath the head ; on its front aspect 

 is a groove within which the mandibles and maxillae, trans- 

 formed into fine, needle-like piercers work to and fro. Thus 

 the aphid, pressing the tip of its beak against the surface of 

 a leaf, can perforate the plant-tissue with its piercing jaws 



FIG. 38. COMMON COCKROACH (Blatta orientalis). 

 a, female ; 6, male, dorsal views ; c, female, side view ; d, young 

 with wing-rudiments. Natural size. From Carpenter, " Life Story 

 of Insects," after Marlatt, Entom. Bull. 4, U.S. Dept. Agric. 



and suck in a meal of sap through the narrow channel between 

 them. 



Most aphids pass the winter in the shelter of hard-shelled 

 eggs laid on suitable plants during the previous autumn. 

 From these eggs are hatched in the spring young insects 

 (Fig. 39 d) which grow through a series of moults but with 

 hardly any change of form into wingless females (Fig. 39 c) 

 known as " stem-mothers ". There are no males for these to 

 mate with, and they have the power of producing young which, 

 developing from unfertilized eggs within the mother's body, 

 are born in an active state, and may themselves become adult 



