98 



NUTRITION. 



the interior of the body. When the food has been sufficiently 

 digested there, it passes, by imbibition, into the general cav- 

 ity of the body, (c,) which is filled with water, and mingling 



with it, flows thence into all parts of the an- 

 imal. The jelly-fishes, (Medusas,) and 

 some Worms, have a distinct stomach, with 

 appendages branching off in every direction, 

 (Fig. 31,) in which a more complete elabo- 

 ration takes place. The little worms known 

 by the name of Planaria, present a striking 

 example of these ramifications of the intes- 

 tine, (Fig. 49, e.) But here, likewise, the 

 product of digestion 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 cavities of the intestine 

 vary considerably, according to the mode of life of the ani- 

 mal ; but the special functions assigned to them are invaria- 

 ble ; and the three principal cavities succeed each other, in 



Fig. 50. 



