THE SNAIL. 383 
terrestrial animals, breathing air directly through a pulmon- 
ary chamber, and drowning (slowly) when immersed in 
water. Their food consists of leaves and other parts of 
plants, but they sometimes indulge in strange vagaries of 
appetite. They are hermaphrodite, but there is always 
cross-fertilisation. The breeding time is spring, and the 
eggs are laid in the ground. In winter snails bury them- 
selves, usually in companies, cement the mcuths of their 
shells with hardened mucus and a little lime, and fall into a 
state of ‘latent life,” in which the heart beats feebly. They 
have been known to remain dormant for years. 
Fic. 208.—Vertical section of the shell of a species 
of Helix, : 
™., Mouth of shell; A., apex; C., columella. 
General appearance.—A snail actively creeping shows a 
well-developed head, with two pairs of retractile horns or 
tentacles, of which the longer and posterior bear eyes. The 
foot, by the muscular contraction of which the animal 
creeps, is very large ; it leaves behind it a trail of mucus. 
The viscera protrude, as if ruptured, in a dorsal hump, 
which is spirally coiled and protected by the spiral shell. 
On slight provocation the animal retracts itself within its 
shell, a process which drives air from the mantle cavity, and 
thus helps indirectly in respiration. Around the mouth of 
the shell is a very thick mantle margin or collar, by which 
the continued growth of the shell is secured. On the right 
