88 



DIGESTION 



but all is so digestible that 

 no undigested food is found 

 in them, there is nothing to 

 soil their waxen cells, and 

 economy and sanitation 

 march hand in hand. 



In animals such as we are 

 now considering the alimen- 

 tary canal is embedded in 

 the otherwise solid body and 

 moves as the body moves. 

 If the latter stretches, the 

 digestive system stretches ; 

 if it contracts, the alimen- 

 tary canal also contracts. 

 The latter may branch 

 throughout the solid tissues 

 of the animal, but the long- 

 est branch is never lonjxer 

 than the animal. 



Body-cavity 



In higher animals, how- 

 ever, a second cavity arises, 

 the body-cavity. This is 

 bounded on the outside by 

 the skin and underlying 

 muscles and on the inside 

 by the muscular walls of 

 the alimentary canal. The 

 body-cavity is traversed by 

 the stomach and intestine, 

 and it houses, besides, the 

 large glands connected 

 therewith, the liver and 

 jDancreas, also the heart, 

 the lungs, and the kidneys. 

 Although in many of the 

 simpler animals, e.g. the 

 earthworm, the alimentary 

 canal passes straight from 



- 4 



Fig. 33. Diagram of digestive and excre- 

 tory system of the Liver-fluke, Distomum 

 hepaticum. Magnified about 8. From 

 Leuckart. 1. Mouth. 2. Pharynx. 3. Re- 

 productive pore. 4. Branch of alimen- 

 tary canal. 5. Branches of excretory 

 system. 6. External opening of excretory 

 system. 7. Nerve-ring. 



