310 



THE ANIMAL KINGDOM 



Testis and Spe-rm duct 



Hea-T-tn 

 <KRcctixm 



Malpi^hiantiibul^s Sali^^ary reservoir 



Salivary glands 



soph ados 

 rBrain. 



EjaLCulat-ory 



haT3?rT)C 



plna^e^ 



Mou.th.-J ganglion. 



Seminal vesicles 

 Ne-rve ganglion- 

 Figure 16.20. Internal anatomy of the cockroach (male). (After Metcalf, Flint and 

 Metcalf.) 



the stomach has eight digestive pouches. The stomach curves around 

 to the anterior end of the abdomen where it joins the hindgut. This 

 includes a long intestine and a short rectum, lined with chitin. The 

 stomach is lined with a simple gastrodermis, surrounded by thin cir- 

 cular and longitudinal muscle layers. The gizzard projects into the 

 stomach, and the posterior cells of the foregut secrete chitin contin- 

 uously, forming a tubular peritrophic membrane that surrounds the 

 food as it passes through the stomach and intestine. This remarkable 

 structure is found in many insects. 



Digestion occurs primarily in the crop. Secretions from the digestive 

 pouches are passed forward as in the crayfish. Mechanical breakdown 

 is aided by the gizzard, and the finely pulverized and digested food is 

 then passed into the stomach. Water and dissolved nutrients diffuse 

 through the peritrophic membrane to be absorbed by the lining of the 

 stomach and digestive pouches. The remaining water is absorbed in 

 the intestine, leaving dry fecal pellets to be eliminated through the anus. 



At its anterior end the intestine receives six groups of delicate 

 Malpighian tubules. These are blind tubules lying in the hemocoel. 

 They pick up waste from the blood and excrete it into the intestine. 

 Nitrogenous wastes are excreted as uric acid, an adaptation which con- 

 serves body water (p. 95). Each tubule has a muscular coat and its 

 slow writhing aids the passage of wastes down its lumen. These are the 

 excretory organs of all labiates. 



The brain (Fig. 16.20), formed from three parts as in the Crustacea, is 

 a bilobed structure lying over the esophagus. The subesophageal gang- 

 lion is formed by fusion of the remaining three pairs of head ganglia 

 and lies beneath the esophagus. These are connected by stout circum- 

 esophageal connectives forming a nerve ring around the esophagus. 

 The ventral cord continues posteriorly with three thoracic and six ab- 

 dominal pairs of ganglia. The last pair supplies all of the remaining 

 abdominal segments. 



The compound eyes of insects are remarkably like those of crusta- 

 ceans. Each ommatidium of the cockroach has the same general parts, 



