TERRESTRIAL. 



The terrestrial molluscs of Great Britain have now 

 to be considered. Although the greater number live 

 entirely on land, some of them are capable of remain- 

 ing submerged for a considerable time. 



With respect to animals of a higher organism there 

 is a true and common saying, that it is impossible to 

 determine the point at which instinct ends and reason 

 begins, and in the case of these humbler creatures of 

 the Great Artificer's hand, it is equally impossible to 

 detect a single flaw or gap in the chain which unites 

 them not only to one another, but to beings of a 

 higher as well as of an inferior order, so deftly and so 

 imperceptibly are its links graduated. 



The terrestrial molluscs, like the LimnceidcE, belong 

 to the second order {Pulmonobranchiatd), and are com- 

 prised in five families which for convenience' sake may 

 be divided into three sections. The first section con- 

 tains three families, and the animals comprised in it 

 resemble the LimnceidcE in most respects, but their ten- 

 tacles are retractile instead of contractile. The second 

 section contains only one family, which has a still 

 closer affinity to the LimncBidcB, inasmuch as the ten- 

 tacles of the animals which belong to it are contractile, 

 and their eyes are placed at the base instead of on the 

 tips of the tentacles. The third section consists of one 



