12 



are probably covered with cilia in more or less active 

 motion, for all the portions of the lining of the stomach 

 and intestine examined by me appeared to be provided 

 with a ciliary covering. The faeces of the oyster are not 

 extruded in the form of a cylinder as in many other 

 mollusks, but have the form of a demicylinder with one 

 side excavated in a groove-like manner, as shown in 

 section in Fig. I, 2, the peculiar form being dne to the 

 presence of the longitudinal folds in the intestine, as shown 

 in a cross-section of the latter in Fig. I, 1. In Unio^ the 

 fresh-water mussel, a similar arrangement is said to 

 exist, according to Bronn ; (Klass. u. Ord. des Their- 

 reichs. III, p. 364.) 



The course of the intestine as sketched above is most 

 nearly in accord with Clark's account ; the hgiires given 

 by Sir Everard Home^ of the intestine of Ostrea edulis 

 are also in close agreement, but the proper relation of 

 the mouth and palps was evidently not understood. 

 Home's figure, however, fully justihes, with other evi- 

 dence, the criticism made in Woodward's Manual of the 

 Mollusca, regarding the inaccuracy of Poli'sf figures of the 

 same parts. 



The systemic heart is that organ .which serves to pro- 

 pel and continually redistribute the colorless blood of 

 the oyster through the body for its nourishment, and 

 through the gills that the blood itself may discharge into 

 the; water the poisonous gases with which it is load- 

 ed in passing through the body, and receive a fresh 

 supply of oxygen as fresh supplies of water pass through 

 the gills. The heart consists of three chambers ; the 

 upper and largest is the ventricle ve. and the two small- 

 er, lowermost, brownish, paired chambers are called 

 auricles au ; the three chambers lie in a crescent- shaped 

 space, the pericardial space Per, just forward of the 

 adductor muscle. The ventricle ve^ is almost globular ; 



*Philos. Trans. 1827. pi. IV. 



fTestacea Utriusque Siciliae eorumque Historia et Anatome, II. Tab. XXIX, fig. 3. Parma, 

 1795, Fol. 



