188 ARTHROPODA. 



(a) The esophagus, which bends backward from the mouth, 

 gradually enlarges as it enters the thorax. 



(b) The crop, which is not sharply separated from the esoph- 

 agus, gradually narrows posteriorly. 



(c) Following the constriction posterior to the crop is the 

 elongated stomach, frequently called the ventriculus. Surround- 

 ing the anterior end of this portion are a series of rather large 

 diverticula, the gastric cceca, that extend both anteriorly and 

 posteriorly from the points where they open into the stomach. 



{d) Some distance behind the posterior ends of the hepatic 

 caeca, quite concealed by the mass of small uriniferous tubes, is a 

 slight constriction and hardening of the alimentary canal that 

 marks the division between the stomach and intestine. It is at 

 this point that the uriniferous tubes join the alimentary canal. 



(e) Behind the intestine the alimentary canal becomes much 

 smaller and is known as the hind intestine or colon. 



(/) Behind the colon, forming the hinder portion of the ah- 

 mentary canal, is the slightly enlarged rectum. The rectum 

 cannot be seen until the ovary is removed, which should be de- 

 ferred until the ducts have been seen. 



Make a drawing showing the position of the parts of the alimen- 

 tary canal in side view. 



Cut the intestine and turn the alimentary canal posteriorly 

 and anteriorly. 



5. Notice the muscles: 



(a) That move the abdominal segments. 



(5) That move the legs (those that supply the wings have 

 been destroyed). 



(c) That move the jaws. 



Do you understand now why the thorax needs to be compar- 

 atively large and firm? 



6. The nervous system is directly comparable to that of the 

 lobster, but the connectives between the ganglia will be found 

 to be distinctly double and the ganglia to be somewhat differently 



arranged.^ 



1 The arrangement of the ganglia in insects is very variable, showing 

 many gradations in concentration. 



