SEA-FISHERIES LABORATORY. 187 
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 itis 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. Hither 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 
