THE SEA SNAIL. 67 
columellar muscle. Detach it and strip off all parts 
of the shell. Kill by immersion for a few minutes in 
vinegar and water. Pin out, under salt water, with 
two pins passed through the foot, the operculum being 
below. The pallial cavity formed by the mantle over 
the neck will be found to be closed, the mantle being 
joined to the head, except a small opening on the 
right side just behind the head. This closed pallial 
chamber is the pulmonary sac, and the opening the 
pulmonary opening ; behind the opening is the anus, 
Put the point of the knife or scissors into the pulmo- 
nary opening and cut the mantle transversely across 
the back of the neck ; commence again at the opening 
and cut longitudinally towards the middle of the back 
of the animal. Turn the cut flap over to the animal’s 
left. Notice on the roof of the cavity the renal organ, 
shaped something like a feather and having a minute 
opening at its point. Hxamine a portion. The floor 
of the pulmonary sac is formed by a delicate, trans- 
parent membrane (homologous with the dermis) 
through which some of the other organs can be seen ; 
notably the orange-coloured albumen gland, sur- 
rounded by coils of the intestine. At the anterior 
left-hand corner of the pulmonary sac, at the base of 
the renal organ, will be seen the pyriform yellowish 
heart, the auricle connected with the roof of the sac 
by the pulmonary vein. Passing backwards is the 
aorta, which soon divides into two. Round and below 
the heart passes a coil of the intestine, easily distin- 
guished by its longitudinally striped appearance, 
caused by foldings. 
3. Alimentary system.— Lower down, and rather to the 
left of the median line, will be found the cesophagus. 
