lt^Hp-sH^ils 



UR introduction to the Land- 

 Snails must be made through 

 a few species that may appear 

 to belong to the previous 

 chapter and to have been forgotten when that 

 was written. They are slugs it is true, and until 

 quite recently they were classed with the true 

 slugs of the genus Limax, but of late they have been 

 separated as having closer affinity with snails of the 

 genus Helix — they may, indeed, be said to fall in with 

 the popular and ancient definition of a slug, which 

 says it is a snail that has cast off or not yet developed 

 its shell. The slugs of the genus Avion have not 

 even the debased shell — the mere scale that, hidden 

 by the mantle, protects the respiratory chamber in 

 Limax; in Avion it is represented by a few dis- 

 connected granules of shell-matter covered by the 

 hinder part of the mantle. They may be distinguished 



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