COCKROACH. 



293 



ten pairs of lateral apertures or stigmata, ramify throughout 

 the body, and have a chitinous lining throughout. 



Circulatory system.— The chambered heart lies along 

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

 blood by lateral valvular apertures from the surrounding 

 pericardial space, and drives it forwards by a slender aorta. 

 The blood circulates, however, within ill-defined spaces in 

 the body. 



Excretory system. — There are sixty or so fine (Mal- 

 pighian) tubules, which rise in six bundles from the begin- 

 ning of the ileum, and twine through the "fatty body" 

 and in the abdominal cavity. The absence of nephridia 

 in insects has already been noted. 



Reproductive System. 



Sixteen ova, one from each ovarian tube, are usually 

 enclosed within each egg-capsule. The latter is formed 



