NUTRITION IN THE ASTERIAS. 101 



and which is properly the stomach. From this 

 central sac there proceed ten prolongations, or 

 canals, which occupy in pairs the centre of 

 each ray, or division of the body, and subdivide 

 into numerous minute ramifications. These 

 canals, with their branches, are exhibited at c, c, 

 Fig. 258, which represents one of the rays of the 

 Asterias, laid open from the upper side. The 

 canals are supported in their positions by mem- 

 branes, connecting them with the sides of the 

 cavity in which they are suspended. 



In the various species of Echini, we find that 

 the alimentary tube has attained a more perfect 

 developement ; for instead of constituting merely 

 a blind pouch, it passes entirely through the body 

 of the animal. We here find an oesophagus, or 

 narrow tube, leading from the mouth to the sto- 

 mach ; and the stomach is continued into a 

 regular intestine, which takes two turns in the 

 cavity of the body, before it terminates. 



The alimentary tube in the lower animals fre- 

 quently exhibits dilatations in different parts : 

 these, if situated in the beginning of the canal, 

 may be considered as a succession of stomachs ; 

 while those that occur in the advanced portions 

 are more properly denominated the great intes- 

 tine, by way of distinction from the middle por- 

 tions of the tube, wdiich are generally narrower, 

 and are termed the small intestine. We often 

 see blind pouches, or c(Eca, projecting from dif-^ 



