76 HELICID^E. 



They have generally been united with the Arions ; 

 but it has lately been discovered that there are 

 animals with well-developed shells that agree with 

 the Arions in character, as the Helices do with the 

 Slugs ; and it has therefore been thought better to 

 separate them by the above character into two 

 groups, rather than follow Lamarck in dividing these 

 animals into groups, by the gradually and greatly 

 varying form of the body. 



The shells are covered with a distinct periostracum. 

 It has generally been believed that shells which are 

 covered with a reflexed portion, or imbedded in the 

 mantle, are destitute of this covering ; and they 

 have been separated from other shells for this reason. 

 But this is an error arising from the theory that the 

 periostracum of shells is analogous to the scarf-skin of 

 vertebrated animals, instead of its being merely the 

 part, consisting almost entirely of animal matter, 

 that is first deposited by the animal when it is about 

 to enlarge its shell, and which forms the basis of the 

 new part of the shell, afterwards strengthened and 

 thickened by the addition of the chalky matter 

 within it. 



These animals sometimes suspend themselves by 

 a kind of thread formed from the viscid secretion 

 which covers their body ; hence one of the smaller 

 ones has been called Limax Jilans. The eggs are 

 covered with a transparent coat, and are often 

 united together by a membrane like a string of beads. 

 They are laid between May and September. They 

 are hatched in about 25 or 30 days, and the young 

 reach their full size near the end of the year. Limax 



