178 ECHINODERMATA. 



mode in which star-fishes attack oysters, although the destruction that 

 they cause is pretty generally acknowledged. The observations re- 

 corded by M. Eudes Deslongchamps upon this subject, however, are 

 exceedingly curious*. As the waves had receded from the shore, so as 

 to leave only one or two inches of water upon the sand, he saw numbers 

 of Asterias rubens rolling in bunches, five or six being fastened together 

 into a sort of ball by the interlacement of their rays. He examined a 

 great number of such balls, and constantly found in the centre a bivalve 

 mollusk (Mactra Stultorum, Linn.) of an inch and a half in length. 

 The valves were invariably opened to the extent of 2 or 3 lines ; and 

 the star-fishes were always ranged with their mouths in contact with 

 the edges of the valves. 



(466.) On detaching them from the shell which they thus impri- 

 soned, he found that they had introduced between the valves large 

 rounded vesicles with very thin walls, and filled with a transparent 

 fluid. Each Asterias had five of these vesicles ranged around its mouth : 

 but they were of very unequal size ; generally there were two larger 

 than the rest, equal in size to large filberts, while the other three were 

 not bigger than small peas. These vesicles appeared to be attached to 

 the Asterias by short pedicles ; and at the opposite end of each was a 

 round open aperture, through which the fluid contained in the vesicle 

 flowed out, drop by drop. No sooner was the animal detached from the 

 shell that it was thus sucking, than the vesicles collapsed and became 

 no longer distinguishable. The Mactrce were all found to be more or 

 less devoured, some having only their adductor muscles left ; but, how- 

 ever little they had been injured, all had lost the power of closing their 

 valves, and were apparently dead : nevertheless there was nothing to 

 lead to the supposition that only dead shell-fishes were attacked; so that 

 it is difficult to imagine how the delicate vesicles above described 

 escaped injury from the closing of the valves. M. Deslongchamps 

 thinks that probably the Asterias pours into the shell a torpifying 

 secretion, and thus ensures the death of its victim. 



(467.) The absorption of the nutritious portions of the food in the 

 Echinodermata is entirely accomplished by the veins distributed upon 

 the coats of the digestive cavities, so that the chyle resulting from 

 digestion is at once introduced into the vessels appropriated to cir- 

 culation. 



(468.) In Asterias, the intestinal veins form a fine vascular network, 

 covering the stomach and the ten digestive caeca. The venous trunks 

 derived from all these sources unite to form a circular vessel (fig. 90, e), 

 which likewise receives branches derived from the ovaria and other 

 sources. 



(469.) The circular vein thus formed, which seems to be the common 

 trunk of the venous system, communicates with another vascular circle 

 * Bulletin des Sciences de M. le Baron Ferussac, vol. x. p. 296. 



