THE STRUCTURE OF INSECTS. 9 



small conical valves closing the passage, thus preventing 

 the regurgitation of the food. The two salivary glands con- 

 sist each of a bunch of follicles, emptying by a common duct 

 into the floor of the mouth. 



The oesophagus is succeeded by the crop (ingluvies). It 

 dilates rapidly in the head, and again enlarges before pass- 

 ing out of the head, and at the point of first expansion or 

 enlargement there begins a circular or oblique series of folds, 

 armed with a single or two alternating rows of simple spine- 

 like teeth. Just after the crop leaves the head, the folds 

 become longitudinal, the teeth arranged in rows, each row 

 formed of groups of from three to six teeth, which point 

 backward so as to push the food into the stomach. It is 

 in the crop that the "molasses" thrown out by the locust 

 originates. 



The proventriculus is very small in the locust, easily over- 

 looked in dissection, while in the green grasshoppers it is 

 large and armed with sharp teeth. A transverse section of 

 the crop of the cricket shows that there are six large irreg- 

 ular teeth armed with spines and hairs (Fig. 5). It forms 

 a neck or constriction between the crop and true stomach. 

 It may be studied by laying the alimentary canal open with 

 a pair of fine scissors, and is then seen to be armed with 

 six flat folds, suddenly terminating posteriorly, where the 

 true stomach (chyle-stomach, ventriculus) begins. The 

 chyle-stomach is about one half as thick as the crop, when 

 the latter is distended with food, and is of nearly the same 

 diameter throughout, being much paler than the reddish 

 crop, and of a flesh-color. 



From the anterior end arise six large pouches called gas- 

 tric cceca, which are dilatations of the true chyle-stomach, 

 and probably serve to present a larger surface from which 

 the chyle may escape into the body-cavity and mix with the 

 blood, there being in insects no lacteal vessels or lymphatic 

 system. 



The stomach ends at the posterior edge of the fourth ab- 

 dominal segment in a slight constriction, at which point 



