110 



AN INTRODUCTION TO ENTOMOLOGY 



is not distinct from the mouth-cavity; but in sucking insects the 

 pharynx is a highly specialized organ, being greatly enlarged, muscu- 

 lar, and attached to the wall of the head by muscles. It is the pump- 

 ing organ by which the liquid food is drawn into the alimentary canal. 

 The pharnyx of the milkweed butterfly (Fig. 125) is a good example 

 of this type of pharynx. 



The oesophagus. The oeso- 

 phagus is a simple tube which 

 traverses the caudal part of the 

 head and the cephalic part of the 

 thorax. There are variations in 

 the application of the term 

 oesophagus depending on the 

 presence or absence of a crop 

 and of a proventriculus, which 

 are modified portions of the 

 oesophagus; when either or both 

 of these are present, the term 

 oesophagus is commonly restricted 

 to the unmodified part of the 

 fore-intestine. 



The crop. In many insects a 

 portion of the oesophagus is dilated 

 and serves as a reservoir of food; 

 this expanded part, when present, 

 is termed the crop. In the cock- 

 roach (Fig. 124) it is very large, 

 comprising the greater part of the 

 fore-intestine ; in the ground-beetle 

 Carabus (Fig. 126, c), it is much 

 more restricted; this is the case 

 also in the honeybee, where it is 



a nearly spherical sac in which 



+1 j ., , Fig. 126. Alimentary canal of Carabns 



the nectar is stored as it is col- \ umtus; h> head;%, oesophagus; c, 



lected from flowers and carried to 



ag-- 



the hive. In some insects the 

 crop is a lateral dilatation of the 

 oesophagus, and in some of these 



auratus; h, head; 



crop; pv, proventriculus; mi, mid- 

 intestine covered with viiliform gastric 

 coeca; mv, Malpighian vessels; hi, part 

 of hind-intestine; r, rectum; ag, anal 

 glands; mr, muscular reservoir (After 

 Dufour). 



it is stalked. 



The proventriculus. In certain insects that feed on hard sub- 

 stances, the terminal portion of the fore-intestine, that part im- 



