ECHINODERMATA. 153 



ing 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 (Jig. 66, Z>), and is a yellow or greenish-yellow racemose 

 sacculus, which opens into the bottom of the digestive sac by a free 

 aperture : the contents of this organ, moreover, resemble bile both 

 in taste and colour.* 



In the slender-rayed genera, such as Ophiuru*, the csecal 

 appendages are not met with ; but their deficiency appears to be 

 supplied by the plicated walls of the stomach itself, the ^nu- 

 merous folds of which resemble lateral leaflets attached to the cen- 

 tral cavity. We are unacquainted with the precise organization of 

 the alimentary canal in Comalula ,- but, from the orifices visible in 

 the shell, it would appear that in this genus, as well as in some 

 Crinoid species, the digestive tube was furnished with an anal 

 aperture. 



(194.) The star-fishes, grossly considered, might be regarded as 

 mere walking stomachs ; and the office assigned to them in the eco- 

 nomy of nature, that of devouring all sorts of garbage and offal which 

 would otherwise accumulate upon our shores. But, as we have 

 already seen, their diet is by no means exclusively limited to such ma- 

 terials, since crustaceans, shell-fish of various kinds, and even small 

 fishes, easily fall victims to their voracity. Delle Chiaje found a 

 human molar tooth in the stomach of an individual which he exa- 

 mined. Neither is the size of the prey upon which they feed so 

 diminutive as we might suppose from a mere inspection of the orifice 

 representing the mouth ; for this is not only extremely dilatable, 

 but, as we have found to be the case in the Actiniae, the stomach 

 is occasionally partially inverted, in order more completely to 

 embrace substances about to be devoured. Shell-fishes are fre- 

 quently swallowed whole ; and a living specimen of Chama anti- 

 quata, Lin., has been taken from the digestive cavity of an Asterias 

 in an entire state. It appears, moreover, that it is not necessary for 

 testaceous mollusca to be absolutely swallowed, shells and all, to 

 enable the Asteridse to obtain possession of the enclosed animal, 

 as they would seem to have the power of attacking large oysters, 

 to which they are generally believed to be peculiarly destructive, 

 and of eating them out of their shells. The ancients believed that, 

 in order to accomplish this, the star-fish, on finding an oyster par* 



* Delle Chiaje, op. cit. 



