DIGESTIVE SYSTEM. 49 



body, as in Gamasus. Anus generally terminal, rarely in 

 middle of ventral surface of abdomen, as in Acarus. 



Salivary secretion universally present. Hepatic secretion 

 from follicles either simple, as in Trombidium, or multiramose, 

 as in Epeira. 



Insecta. Intestine can be divided into gullet, crop, giz- 

 zard, small intestine, large intestine, and rectum. Anus 

 terminal. Great variation among different orders of insects 

 with respect to the form and length of the canal. Coleop- 

 tera have crop, followed often by an ovoid gizzard. The 

 small intestine is often longer and more convoluted in the car- 

 nivorous than in the herbivorous families. Orthoptera have 

 gizzard armed with rows of horny denticulated plates. Hym- 

 enoptera, with simple, thin, and dilated sucking stomach. 

 Hemiptera, with compound stomach, consisting of two or 

 three chambers. Diptera, with sucking stomach, commonly 

 pedunculated. 



Salivary secretion elaborated in csecal tubes, sometimes of 

 great length, which open into the oral cavity. Hepatic secre- 

 tion from gastric cells, or long simple cseca. A fluid, analo- 

 gous to the pancreatic secretion, flows from follicles appended: 

 to the small intestine. The connection we find existing be-- 

 tween the alimentary canal and food of Vertebrata the for- 

 mer being simple when the food is simple, complicated when 

 much preparation is required of the food does not subsist 

 to the same degree among insects. Thus the Tenebrionidse, 

 which subsist on wood, have a comparatively simple canal, 

 while Lepidopterous insects, living on honey, have a much, 

 more complicated one. 



VERTEBRATA. Pisces. Gullet short, wide, and ends in, 

 stomach by a slight constriction ; regurgitation readily 

 effected. Long fleshy processes from the mucous membrane 

 project backward as in Selachia (sharks). Stomach gen- 

 erally simple. Gizzard-like structure in Salmofurio (Gillaroo- 

 trout). Intestine short, with few exceptions. Convoluted, 

 in a few Cyprinoids, rarely coiled around the air bladder 

 (Campostomci). Anus commonly directly in advance of anal 

 fin. Except Gymnotus (electric eel), and Aphredoderus, where- 



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