332 Mr. W. Clark on the Pholadidse. 



tubular mantle which contains the liver, ovarium and pericar- 

 dium, in a distinct independent membrane that may be called a 

 peritoneum, and in their passage under these organs they furnish 

 them with filaments, and then piercing the fundus of the peri- 

 toneum enter the pericardium, and form a junction with a second 

 larger ganglion that is fixed in that cavity in some measure en- 

 veloped by the heart and auricles, and is only visible when the 

 pericardium is cleared of them : this mass supplies the terminal 

 part of the ovarium, the entire branchiae, and all the posterior 

 parts of the body with nervous threads. 



The digestive organs next present themselves. Authors have 

 said there are two distinct stomachs ; this is not so : they have 

 mistaken the peritoneal cavity containing the liver, ovarium and 

 pericardium, for one : the true and only stomach is within the 

 hemispherical valves, in immediate contact with the greenish 

 brown liver that pours the bile into it from above ; it is very 

 small ; the walls are simple ; and the elastic stylet and gizzard, 

 which some naturalists denominate the tricuspid membrane, 

 work within it as a gizzard and attritor. 



I have carefully dissected the apparatus of the present species, 

 and have it on a card in a united state, showing the hard horny 

 parts of the rubbing portion. Some authors say that this machine 

 is not to be found in all bivalves. Which ? I am inclined to think 

 that none are without it. 



The mouth is a triangular V-shaped aperture placed imme- 

 diately above the foot ; on each side there is a palpar or salivary 

 mass, which from its wavy streamlets appears to be of the latter 

 quality ; they have a glandular aspect, and may perhaps combine 

 tentacular uses. The mouth opens into a short oesophagus which 

 descends into a small stomach, the contents of which under the 

 microscope appeared to be wood reduced to a pulpy mass, that 

 after having undergone the action of the gizzard is discharged 

 into the intestine, which, as soon as it springs from the pylorus, 

 mounts to the integuments that divide the dorsal aperture from 

 the peritoneal cavity, passing through them and showing from 

 without a tubular inflation that has been mistaken for the oeso- 

 phagus of the second stomach, but is undoubtedly an intestine, 

 which I have traced and opened throughout its length ; it pro- 

 ceeds in a straight line through the liver to about the centre of 

 the ovarium for 1 inch ypths, when, by a sudden short turn, it 

 retraces its steps for y^ths of an inch, when it again turns and 

 makes an oblique reach of about ^ an inch, and then makes a 

 further gyration, and forms a complete but small sigmoid flexure, 

 and pursues its course for 1 inch y'^jthsto the anterior part of the 

 body, which it descends, coasting for y^yths of an inch the foot 

 to the external pyloric point of the stomach, and becoming a short 



