HELIX. 175 



the slightest pressure ; while in others, their defensive 

 strength suits well wdth the lives of those that have to 

 sustain the dangers of a stormy element and a rocky 

 bottom, as well as the attacks of voracious fish. The sealing 

 up of the aperture of the shell, which serves in several 

 species as an effectual protection against the cold of winter, 

 is, also, admirably adapted for security as well as w^armth. 

 But the epiphragm is not of the same substance as the 

 shell ; evidently because the animal w^ould be then unable 

 to break down the enclosing barrier, when the retm-n of 

 spring invites him from his winter quarters. In the midst 

 of an almost endless variety, a striking regularity is never- 

 theless discoverable. However different individuals may 

 vary in form and colour, according to the sites which they 

 are designed to occupy, in one point they almost univer- 

 sally agree : — the number of whorls in the same species 

 is generally, if not always, the same ; and these, with a 

 few exceptions, are uniformly in one direction, that is, from 

 right to left, like the motion of the globe, when the mouth 

 of the shell is turned northward, with the base towards 

 the ground. 



The common snail is soft, spongy, and transparent, and 

 is provided with horns, or tentacles, at the extremities of 



