of Mollusks in Holothuria?. 33 



cavity, a space which exists independently of the movements of 

 the mollusk ; within it, two series of long vibrating filaments are 

 visible; one series runs longitudinally down the cavity of the 

 shell, following its curvature, and then bending round towards 

 the body of the mollusk ; the second series runs in a more trans- 

 verse direction. The mouth leads into a wide oesophagus, which 

 passes above the two auditory organs. The stomach and in- 

 testine are similar to those of other young mollusks. The intestine 

 forms a loop in the shell, whose returning limb, the rectum, bends 

 to the right. The liver consists of relatively small cells. In the 

 vicinity of the rectum, a few yellow granules may always be seen, 

 like remnants of the yelk. The innermost part of the shell, nearer 

 the apex, is filled by a transparent vesicular part of the body, 

 which is penetrated by several thread-like cords, and thence ap- 

 pears vesicular. Yellow granules, similar to those just described, 

 often lie among the threads, as if in the interspaces of vesicles. 

 Sometimes the animals come out of their shells, and then the 

 structure of this part is still clearer. In animals which have 

 been freed by injury of the shell, or the like, the gill-cavity is 

 torn, and the remains of the vibrating gill-filaments remain at- 

 tached and uncovered. 



The mollusks could be kept alive many hours by placing the 

 vesicles containing them, or the sacs, in the abdominal fluid ob- 

 tained by cutting open a Synapta. In the water they died 

 sooner. 



It would be extremely difficult to decide upon the exact zoolo- 

 gical affinities of this mollusk. The presence of the operculum 

 is not a character on which any great reliance can be placed, 

 since mollusk-larvse with deciduous shells, such as the Nudi- 

 branchiata and Tectibranchiata, possess one. But the possession 

 of a respiratory cavity, the calcareous nature of the shell, the 

 more developed spire, and its decidedly symmetrical curvature, 

 seem to me to indicate that we have to do with one of the Pectini- 

 branchiata. If, however, the shell of this mollusk be deciduous, 

 the gill-cavity, which now extends far into the shell, must become 

 wholly changed. 



That the mollusks are developed within the Holoihuria is 

 clearly made out ; how it is possible that they are so developed, 

 I know not. All that I know is the fact, and the mode in which 

 it occurs ; and I may further add, that it is impossible the mol- 

 lusks should have been introduced by any one from without. 

 The Holothuria has not eaten them, for it eats nothing but fine 

 earthy mud, and nothing else is ever found in its intestine; and 

 even if it had, how could they get out of the intestine into the 

 abdominal cavity and the molluskigerous sac? Neither have 

 they crept into the abdominal cavity of the Synapta- fragments, 



Ann. % Mag. N. Hist. Ser. 2. Vol. ix. 3 



