BLATTA. 227 



The cavity of the gizzard is oontinued into that of the 

 mesenteron, a comparatively short tube which leads into a 

 still shorter and narrower intestine, terminating in a 

 vesicular rectum. At the front e^d of the mesenteron are 

 eight (or nine) hepatic cceca or hollow glandular processes, 

 and at its hind end are six tufts of extremely fine long 

 processes, called the malpighian tubules. They constitute 

 the excretory organs of the cockroach. The rectum has six 

 longitudinal folds. As in the lobster, the mesenteron alone 

 is formed from endoderm, and absorption is confined to it. 

 The parts in front and behind are formed of ectoderm and 

 are lined by chitin. The digestive fluid from the caeca 

 is said to pass forwards into the crop where it is mixed 

 with the food. . Here the food is digested or reduced to 

 a soluble condition. The gizzard then relaxes and allows 

 the digested food to pass on into the mesenteron, in 

 which absorption is effected. The most important dif- 

 ferences in the alimentary system from that of the lobster 

 are (i) the presence of salivary glands (connected with the 

 terrestrial habit) ; (2) the division of the "stomach" into a 

 large storage crop and a small gizzard ; and (3) the presence 

 of excretory organs opening into the alimentary canal. 



The cockroach has a complex system of muscles. In 

 the abdomen the dorsal and ventral abdominal muscles are 

 little modified. They serve to execute the 

 respiratory movements, not to flex the abdomen. 

 In the thorax the muscles are broken up into special limb 

 muscles, moving the legs and wing-muscles for flight. The 

 alary muscles run as a triangular band from the tergon of 

 each segment towards the heart, spreading out under the 

 pericardial septum and meeting its fellow below the heart. 

 They may serve to move the pericardial septum. 



As in the lobster, the muscles are attached to the exo- 

 skeleton but there is no endophragmal skeleton. The cavity 

 of the body is largely filled up by the corpus adiposum or 

 fat body, a mass of fat cells. 



Blood- ^^^^ heart is a long delicate tube running in 



the median dorsal line of the thorax and abdo- 



men. It lies just under the terga. In each 



segment (three thoracic and ten abdominal) it opens by 



paired valves or ostia into the pericardial cavity surround- 



