26 BEITISH MARINE TESTACEOUS MOLLUSCA : 



aid of the extraction of the vital principle. The mouth leads 

 by a short oesophagus into the stomach, concerning which, 

 the elastic stylet, and the tricuspid membrane or stomachal 

 attritor, we refer to the account of the digestive organs of the 

 Pholas dactylus. 



The food of the bivalves appears to be animalculse and soft 

 Crustacea. From the stomach, which is of suboval or pear- 

 shape form, the intestine plunges obliquely into the lower part 

 of the body, amidst the ovarium, and forms 2-5 or 6 convo- 

 lutions, and at the last turn it ascends to the dorsal range, and, 

 as rectum, discharges at the posterior extremity, either into an 

 anal tube, as in the Pholades, Myce, &c., or without one, fixed 

 externally or floating free, as in the Pectines and Anomice. 

 The liver is usually a large, green, granular viscus, on the 

 dorsal region, almost enveloping the stomach, into which it 

 pours the bile by several ducts or orifices. 



The reproductive organs scarcely require mention, as they 

 are largely noticed in the anatomy of the Pholas dactylus, 

 above alluded to. We may, however, say, that all the bivalves 

 are strict hermaphrodites without congression. The ovarium 

 varies greatly in form and consistence at different seasons ; in 

 winter it has generally the aspect of homogeneity, but when 

 under the stimulus of the genial months it becomes tumid, 

 flaky or granular, and as fecundation advances the congeries 

 of ova appear in progressive development until the term of 

 gestation is complete, when they are ejected and deposited on 

 various marine receptacles. These animals, though termed 

 self-sufficient, have doubtless mixed up with their ovaria the 

 male influences, which are apparently minute pear-shape bodies, 

 only discoverable in the genial season, containing a glairy 

 fluid, which may be to communicate the vital spark. In some 

 genera, as Anodon, Mytilus, and a few others, the ova are 

 deposited for a time amongst the network or interspaces of 

 the branchial laminae, in which they are further developed, and 

 become testaceous, when they are finally ejected. 



In reference to the secretions already spoken of elsewhere, 

 we will only observe that the mantle envelopes the entire 

 animal ; its edges are often ciliated, and the posterior end 



