INSECTA ^ 387 



segments in the female and the 9th segment in the male there are 

 paired structures known as gonapophyses which perform various 

 reproductive functions (oviposition in the female, copulation in the 

 male). It is highly probable that these are modified appendages. 



The alimentary canal (Fig. 290) varies greatly in length ; in many 

 larvae it is no longer than the animal itself, but in certain types of 

 insects like the Homoptera, which feed on plant juices, it is much 

 coiled and may be several times the length of its possessor. It consists 



ant' 



p.WM 



Fig. 289. To illustrate the mechanism of wing movement in an Aphid. 

 Wing depression: A, side view of mesothorax; B, transverse section. Wing 

 elevation: C, side view of mesothorax; D, transverse section, ant. anterior; 

 dv.m. dorsoventral muscles; post, posterior; l.m. longitudinal muscles; 

 p.w.a. pleural wing attachment; t.w.a. tergal wing attachment. Effective 

 muscles shown by dotted lines in A and C. After Weber. 



of an ectodermal stomodaeum or fore gut, an endodermal mid gut 

 and an ectodermal proctodaeum or hind gut. The fore gut consists of 

 {a) the buccal cavity succeeded by {b) the pharynx, which may be 

 muscular and form a pumping organ (Fig. 309 A), [c) the oesophagus, 

 which has a posterior dilatation, the crop. This functions as a food 

 reservoir and may have a diverticulum enormously developed in 

 sucking insects to store the liquid food. Lastly there is {d) the pro- 



25-2 



