162 THE COCKROACH 



b. The mesenteron is a short narrow tube extending 



backwards from the hinder end of the gizzard. 

 Lay the mesenteron open and note the funnel-like prolon- 

 gation of the gizzard extending into it. 



c. The proctodoeum is the convoluted hinder portion 



of the alimentary canal, and is lined by a thin 

 chitinous cuticle. It is divided into the following 

 regions. 



i. The ileum is a short narrow tube, the commence- 

 ment of which is marked by the attachment 

 of the numerous fine thread-like Malpighian 

 tubules. 



ii. The colon is much wider and longer than the 

 ileum, and is constricted at its hinder end. 



iii. The rectum is the short dilated terminal portion 

 of the alimentary canal. Its wall has six 

 longitudinal ridges, projecting internally. It 

 ends at the anus, between the podical plates. 



2. The digestive glands. 



a. The salivary glands are two pairs of diffuse white 

 glands on the sides of the anterior part of the 

 crop. 



The salivary receptacles are a pair of thin- 

 walled sacs, one on each side of the crop, between 

 the two glands of its side. 



The ducts of the receptacles run forwards and 

 unite beneath the nerve-cord at the hinder end 

 of the neck to form a median duct, which runs 

 forwards to open into the mouth, behind the base 

 of the lingua. 



The ducts of the salivary glands unite to form 

 one duct on each side : the two ducts thus formed 

 run forwards and unite beneath the nerve-cord in 

 the hinder part of the neck to form a median 

 duct : this runs forwards between the nerve-cord 

 and the median duct of the receptacles, and opens 

 into the latter at the anterior end of the neck. 



