194 THE BOOK OF NATURE STUDY 



than the appropriate element. It is probable that each of the 

 many hundreds of component eyes receives a picture of a small 

 portion of the surrounding view, the action being comparable 

 to that of a " pin-hole " camera ; and inasmuch as the eye- 

 elements are distributed over the curved sides of the head a 

 fairly complete panorama is obtained. In addition to the two 

 compound eyes, there are situated upon the summit of the head 



three small " simple " eyes (ocelli), 

 arranged in a triangle. Projecting 

 from the front of the head, between 

 the compound eyes, are the antennae. 

 These are delicate organs of touch, 

 as may readily be determined by 

 watching the behaviour of a living 

 wasp ; they are also possessed of the 

 sense of smell, and perhaps too of 

 hearing. The first joint, that next 

 the head, is longer than the rest, and 



FIG. 6 9 .-Part of the compound eye is known as the " scape " ; the re- 

 of a wasp, much magnified. maining joints are set at an angle on 



the scape, and together constitute 



the "flagellum" or "flail." The flagellum of "queens" and 

 workers contains eleven joints, while that of drones contains 

 twelve. Thus there are in all thirteen joints in the antenna 

 of the male, but only twelve in that of the females. The front 

 of the scape is yellow in all sexes of those wasps which build 

 nests on trees, but is so only in the males of ground- wasps. Thus 

 a worker-wasp with a yellow line on the front of the scape 

 may at once be known to come from a nest that is above 

 ground, and probably well situated for observation. The area 

 between the two eyes and below the antennae is known as the 

 " clypeus." 



Jaws. Sunk into the ventral portion of the posterior surface 

 of the head is a large and deep depression, in which is lodged 

 the greater part of the jaw apparatus. The depression has no 

 limiting wall in front, so that its contents can be thrust forward 

 to project in front of the clypeus. The jaws consist of three pairs 

 of appendages or limbs, modified to subserve feeding, namely, 



