ECHINODERMATA. 



(193.) With respect to the exact office of these capacious ap- 

 pendages to the stomach, there exists some diversity of opinion. 



Fig. 66. 



It is scarcely possible that they can be at all instrumental in the 

 digestion of food, the passages by which they communicate with 

 the central cavity being too narrow to admit any solid substance 

 into their interior ; the digestive process would therefore seem to 

 be entirely accomplished in the receptacle into which the food is 

 first introduced. But there is every evidence to prove that, 

 although they can have little part in digestion, they are inti- 

 mately connected with the absorption of nutriment ; and thus, 

 although possessing no excretory orifice, they must be looked upon 

 as strictly analogous in function to the intestinal canal of other 

 animals : the great extent of surface which they present internally 

 would alone lead to this supposition, even did not the nature of the 

 material usually found in them, namely a pultaceous creamy fluid, 

 evidently a product of digestion, abundantly confirm this view of 

 their nature. The matter seems, however, to be put beyond a 

 doubt by the arrangement of the vascular system connected with 

 these organs, as the veins which ramify so extensively through their 

 walls are here, as in other ECHINODERMATA, the only agents by 

 which the absorption of chyle can be effected ; this will be evident 

 when we examine the organs subservient to the circulation of the 

 nutritious fluids. 



Those physiologists who have adopted a different view of the 

 nature of the csecal appendages to the stomach, consider them to 

 be adapted to the secretion of some fluid, and probably represent- 



