170 ■ THE COCKEOACH. 



Cut off the elytra and the wings. Carefully cut through 

 the terga of the abdomen and thorax close to each side, and 

 remove the terga, avoiding injury to the heart, which lies just 

 beneath. 



A. The Circulatory System. 



1. The heart is a straight chambered tube running along 

 the mid-dorsal line of the abdomen and thorax. It 

 receives blood through paired lateral openings or 

 ostia, arranged segmentally, and drives it forwards 

 by rhythmical contractions. 



B. The Digestive and Excretory Systems. 



The alimentary 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 appen- 

 dages. In dissecting the salivary ducts great care must be 

 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 stomodoeum 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 stomodoeum 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 elon- 

 gated fleshy tongue or lingua. 



The salivary duct opens by a median 

 aperture in the angle between the lingua 

 and the labium (fig. 38). 



