162 THE COCKEOACH 



B. The Digestive and Excretory Systems. 



The ahmentary canal, with its glandular appendages, is 

 situated almost entirely in the abdomen, and is enveloped in 

 an opaque-white, dendritic mass, the fat-body. 



Expose and unravel the alimentary canal and its append- 

 ages. In dissecting the salivary ducts great care must he 

 taken not to injure the nervous system in the head. 



1. The alimentary canal is short, and slightly convoluted 

 in its hinder part. It may be divided according to 

 its mode of development into three regions : viz. 

 the stomatodcEum and the proctodoeum, which are 

 invaginations of the anterior and posterior ends 

 of the embryo respectively ; and the mesenteron, or 

 middle portion, which alone is formed from the 

 primitive alimentary tract of the embryo. 

 a. The stomatodoeum has a chitinous cuticular lining, 

 continuous with the cuticular investment of the 

 head ; and is divided into the following regions, 

 i. The buccal cavity is lodged in the head, and its 

 posterior wall is raised up to form an elongated 

 fleshy tongue or lingua. 



The salivary duct opens by a median 

 aperture in the angle between the lingua and 

 the labium (fig. 38). 

 ii. The oesophagus is a narrow tube running from 

 the mouth through the nerve collar and along 

 the neck. It is laterally compressed in the 

 cervical region, 

 iii. The crop is a large thin-walled pyriform sac, 

 extending through the thorax and far into 

 the abdomen. It is not separated by any dis- 

 tinct line of demarcation from the oesophagus, 

 iv. The gizzard, or proventriculus, is a pyriform sac 

 with thick muscular walls. Within it is a 

 series of six large cuticular teeth, and behind 

 them six small elevations covered with setse. 

 Lay the gizzard open to expose the teeth. 



