74 



NUTRITION. 



When the food has been sufficiently digested there, it passes 

 into the general cavity of the body (c), which is filled with 

 water, and mingling with it, flows thence into all parts 



of the animal. The jelly-fishes (Medusse), 

 and some Worms have a distinct stomach, 

 with appendages branching off in every di- 

 rection (Fig. 31), in which a more com- 

 plete elaboration takes place. The little 

 worms known by the name of Planaria 

 present a striking example of these rami- 

 fications of the intestine (Fig. 49, e). But 

 here likewise, the product of digestion, 

 namely, the chyle, mingles with the fluids 

 of the cavity of the body which surround 

 the intestine (d] and its branches, and cir- 

 culation is not yet distinct from diges- 



Fig. 49. tion. 

 206. As we rise in the scale of animals, the functions 

 concerned in nutrition become more and more distinct from 

 each other. Digestion and circulation, no longer confounded, 

 are accomplished separately, in distinct cavities. The most 

 important organs concerned in di- 

 gestion are the stomach, and the 

 small and large intestine. The 

 first indications of such a distinc- 

 tion are perceived in the higher 

 Radiata, such as the sea-urchins 

 (Fig. 50), in which the stomach (s), 

 is broader than either extremity of 

 the intestine. The dimensions and 

 form of the intestinal cavities vary Fig. so. 



considerably according to the mode of life of the animal ; 

 but the special functions assigned to them are invariable ; 

 and the three principal cavities succeed each other, in every 

 animal where they are found, in an invariable order ; first, 



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