PULMONARY GASTEROPODS. 
395 
tables it to dispose of fruit, tender leaves, mushrooms, and other 
substances easily divided. 
At the bottom of the mouth is an oesophagus, or gullet, to which 
Sll cceeds a stomach of moderate size. The intestine lies in folds round 
the liver, which is divided into four lobes, and terminates in a special 
°rifice. 
The little lung of the snail is placed in a cavity, vast for its size, 
J' ls t above the general mass of the viscera, and occupies all the last 
Thai turn of the cavity. 
The mechanism of respiration is as follows : The animal inhales the 
air into its lung by forcibly dilating the pulmonary orifice, which lies 
111 the largest spiral ton of the shell. In order to expel the air 
res pired by the lung, it withdraws its body into the narrower part of 
shell, where it gathers itself up completely, even to its head and 
ket, and by this compression of all its little being it expels the air 
^hich fills it. These respiratory movements, however, are not regular, 
h'R succeed each other only at certain intervals. Life would bo too 
hard for the poor snail were it passed in such violent efforts as would 
he necessary if it respired as the larger animals do. In its case the 
bathing is intermittent and imperfect ; it is merely a rough attempt, 
as it were, at respiration, which becomes perfect in some of the higher 
inches of the animal kingdom. 
The snail has a heart, consisting of a ventricle and auricle, con- 
nected with a well-developed arterial vascular system, while the venous 
System is imperfect. In short, the blood only returns from the various 
Parts of the body to the respiratory apparatus, after traversing lacunae, 
° r air-cells, existing between the several organs. 
The blood of the snail is colourless, or rather of a pale rose colour, 
lightly tinted with blue. They have a rudimentary brain, composed 
01 a pair of thick ganglions, situated above the oesophagus, which 
dre in connection with another pair of ganglions placed below, which, 
to gether, form a sort of collar, or ring. From this ring springs a 
•? r eat number of nervous cords, which are distributed to the mouth, 
“ e tentacles, the lung, and the heart. The skin, in those parts 
covered by the shell, exhibits great sensibility ; it receives a con- 
querable quantity of nervous filament, so that the sense of touch ought 
0 Possess extreme delicacy. 
The tentacles, the skin of which is so fine and so sensitive, are the 
