36 



In the farther dissection of this specimen the adipose 

 tissue may be cut away when necessary to see the parts 

 studied. 



Form of the alimentary canal. — Remove the ventral 

 wall of the head so as to expose the alimentary canal 

 throughout its entire length. 



Make a drawing of the alimentary canal and label the fol- 

 lowing parts : — 



Pharynx. — The somewhat trumpet-shaped part of the 

 alimentary canal immediately caudad of the mouth is the 

 pharynx. 

 ■ (Esophagus. — That part of the alimentary canal which is 

 immediately caudad of the pharynx and which traverses the 

 caudal part of the head and the cephalic part of the thorax 

 is the (Esophagus. It is a straight tube of nearly uniform 

 diameter except when some portion of it is distended by 

 food. 



Proventriculus. — In the caudal part of the thorax the 

 alimentary canal begins to enlarge. This enlargement in- 

 creases gradually caudad until, in the first or second abdom- 

 inal segment, its diameter is twice that of the oesophagus ; 

 then it contracts quite suddenly until its diameter is less 

 than that of the oesophagus ; this enlarged, portion is the 

 proventriculus. It corresponds in function with the gizzard 

 of birds and is very complicated in structure internally. 



Ventriculus. — Caudad of the constriction following the pro- 

 ventriculus, there is a slightly enlarged portion, from the 

 cephalic end of which there project cephalad, four large 

 pouches; this enlargement is the ventriculus or stomach 2iw6. 

 the pouches are the gastric cceca. The two caeca of each 

 side are quite closely united. 



Malpighian vessels. — Emptying into the caudal end of the 

 ventriculus are several, small, very long, and much convo- 

 luted tubes ; these are the Malpighian vessels ; they were 



