STRUCTURE OF COCKROACH 375 



eight club-shaped digestive (pancreatic) outgrowths are 

 connected. 



(3) The hind-gut (proctodaeum) is Hned by a chitinous 

 cuticle. It is convoluted and divided into narrow^ ileum, 

 wider colon, and dilated rectum with six internal ridges. 



Respiratory system.— The tracheal tubes, which have 

 ten pairs of lateral apertures or stigmata, ramify throughout 

 the body, and have a spirally thickened chitinous hning. 



Circulatory system. — The chambered heart lies along 

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



Fig. 213. — Transverse section of insect. — After Packard. 



h., Heart ; j?., gut ; n., uerve-cord ; St., stigma ; tr., trachea ; w., wing ; 



/., femur of leg. 



blood by lateral valvular apertures from the surrounding 

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

 The blood, perhaps better called haemolymph, 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. They are often found to 

 be charged with excretory products (urates), apparently 

 collected and passed into the lumen by the hning cells. 

 The free end of each tubule is closed. The absence of 

 nephridia in insects has been already mentioned. 



