3 38 Shell Life 



the respiratory opening more forward than in that 

 species. This also has the prominent keel. The 

 slime is white or pale yellow. When at rest it 

 contracts itself into an almost globular shape. It 

 occurs in hedgerows and gardens, but its distribution 

 is not nearly so wide as that of L. carinatus, and is of 

 only local occurrence. 



The Pellucid Glass-snail ( Vitrina pellucida), which 

 is frequent under mossy logs and stones in damp 

 woods, has special interest for us because of its 

 intermediate position between snails and slugs. 

 The animal may be called a slug, but it has a shell 

 ordinarily of just sufficient dimensions 

 to accommodate it within, yet of such 

 exceedingly delicate substance as to 

 be little protection from enemies. 

 Simroth believes tliat it is the ances- 

 tral form from which the Slugs have 

 Pellucid Glass-snail and ^ gvolvcd by thc gradual dcgcncra- 



shell (enlarged) i/ in & 



tion of the shell, and its investment 

 by the mantle. It may also be reasonably supposed 

 that in the opposite direction by the development of 

 the shell in size and solidity, such an ancestral form 

 may have originated the Snails (Helix), the thin- 

 shelled Hyalinias marking a stage on the way. Our 

 only native species is very hardy in spite of its 

 delicate covering, and it may more commonly be 

 found in winter crawling over mosses and liverworts 

 than in summer. This hardiness may be partly due 

 to the fact that the eggs are not deposited until 

 autumn, so that the young ones enter upon life at a 

 time when thick-shelled snails have retreated into 

 snug quarters for the winter and have plastered up 



