186 PHOLADID^E. 



tion ensued, but not a particle of the mineral found a passage 

 to the branchial vault ; this result occurred in many specimens, 

 and though the pressure was often considerable before regur- 

 gitation was allowed to take place, still the branchial division 

 of the mantle remained free from the quicksilver. In one 

 experiment the fluid appeared in the lateral tissues; this 

 I attribute to a lesion of the dorsal lateral membranes. 

 2ndly, I found that when there was not the slightest solution 

 of continuity in the fine membrane on which the branchial 

 vessels are fixed on one side, and the interweavings and 

 traceries on the other, which form the roof of the anal siphon, 

 the application of the mercury to that tube gradually filled 

 the whole range of the branchial vessels, which exhibited a 

 very elegant appearance, but no fluid escaped from them into 

 the branchial sac. 3rdly, I repeated many times the first 

 experiment with the view of endeavouring to find a passage 

 through the rectum and intestine on the dorsal range that is 

 embraced by the heart, but without success; if I had suc- 

 ceeded, it would have been impossible to arrive at the stomach 

 and mouth, as the intestine plunges into the body coasting 

 the foot, at which point it is of larger diameter, and always 

 filled with a compacted mass of sand which effectually stops 

 up the passage : this part of the intestine around the foot, 

 from its difficulty and the hardness of the faecal matters, 

 seems analogous to the ascending portion of the colon in 

 man. 



In all these attempts either regurgitation ensued, or the 

 continual pressure of the mercurial column caused lesions. 



This impossibility to pass anything into the rectum pro- 

 bably arises from its sphincter, or one in the anal tube, as 

 the stoppage always occurred at that point where it empties 

 into it. 



4thly, On applying the mercury through the mouth and 

 O3sophagus the stomach was readily filled ; but as soon as the 

 pylorus was passed, a stoppage not to be removed occurred, 

 from the duodenum being, like the colon in the last case, filled 

 with sand ; we may therefore conclude that water can never 

 enter the stomach of bivalves from the anal tube. 



