THE SNAIL. 



3 6 7 



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 mouths 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. 



FIG. 18^. Vertical section of the shell of a species 



of Helix, 



M, 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 



