176 



ECHINODEEMATA. 



seen in the ray g, wherein, the upper walls of the caeca having been 

 removed, their sacculated internal structure is rendered visible. 



(461.) With respect to the exact office of these capacious appendages 

 to the stomach, there exists some diversity of opinion. 



(462.) It is scarcely possible that they can be at all instrumental in 

 the digestion of food, the passages whereby 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 by the receptacle into which the food is first introduced. 

 But there is every evi- 

 dence to prove that, al- Fig. 89. 

 though they can have 

 little part in digestion, 

 the caeca are intimately 

 connected with the ab- 

 sorption of nutriment ; 

 and thus, although pos- 

 sessing 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 ma- 

 terial usually found in 



them, namely, a pultaceous creamy fluid, evidently a product of diges- 

 tion, 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 that ramify so ex- 

 tensively 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. 



(463.) Those physiologists who have adopted a different view of the 

 nature of the caecal appendages to the stomach, consider them to be 

 adapted to the secretion of some fluid, and probably representing a 

 biliary apparatus. Their enormous extent, however, would alone lead 

 us to dissent from such a conclusion, more especially as another organ 

 has been pointed out to which the functions of a liver have been assigned. 

 This is situated upon the base of the stomach (fig. 89, 5), and is a 

 yellow or greenish-yellow racemose sacculus, which opens into the 



Digestive apparatus of Asterias : a, stomach ; b, hepatic (?) 

 glands ; c, d, e, csecal appendages in situ if, the same unravelled ; 

 .9, the same laid open, showing their sacculated interior. 



