10 



mantle' edge is first lost; the foot never becomes quite 

 insensitive. The animal is then killed in a 20% solution 

 of formol, a small piece of wood having been previously 

 placed between the edges of the valves to prevent the slow 

 contraction of the adductor muscles which occurs after 

 death. Only a slight amount of contraction takes place 

 in the formol, the siphons and foot being generally moder- 

 ately extended. If it is desired to prepare the animal for 

 sectioning, both valves are removed by placing it in a 10% 

 solution of nitric acid in 70% spirit; if for dissection, it is 

 propped up on a couple of glass slides in a dish with the 

 shell margin horizontal, and the acid solution poured in so 

 as to cover one valve. Either of the two valves can be 

 dissolved off in this way, the other being left to fix the 

 animal in the dissecting dish. A great inconvenience is 

 caused by the accumulation of carbon dioxide, resulting 

 from the decomposition of the shell, within the cavities of 

 the body. If the specimen is being prepared for section- 

 ing, it is best to remove this gas by allowing it to remain 

 for some days in 70% spirit containing a little ammonia. 



Except at the margin, and for a reddish strip at the 

 dorsal surface which is the pallial portion of Keber's organ, 

 the mantle lobe is thin and transparent. Removal of this 

 by cutting along the line Mn'. seen in fig. 2, exposes the 

 gills and labial palps. The gills pass obliquely backwards 

 from the dorsal surface of the body beneath the umbo at an 

 angle of about 30° to the vertical axis of the viscero-pedal 

 mass. 



The labial palps are triangular in shape. Their shorter 

 or anterior sides are attached to the body-wall, and their 

 most anterior extremities pass into the upper and lower 

 lips respectively. The dorsal margins are thin, smooth, 

 and slightly uneven. The internal surface of the outer, 

 and the external surface of the inner palps are marked 



