WILD LIFE OF ORCHARD AND FIELD 



ning water, where the bottom is rocky, such as 

 the members of the famiHes Viviparidae and Stre- 

 pomatidae. All such alterations are gradual, and 

 imply a comparatively long life. 



Another curious thing is to be noticed in this con- 

 nection : whole species sometimes suddenly die out. 

 Not only a conchologist, but any one travelling 

 through certain parts of our western territories, 

 must be struck by the prodigious quantities of dead 

 snail-shells scattered over the ground. These are 

 the Helix cooperi, of which a few are still living in 

 nooks and corners of the mountains. They are 

 of all sizes, degrees of variation, and ages, and lie 

 bleached in millions on the surface of the ground. 

 Mr. E. L. Layard, in a letter to the London Field, 

 mentions a precisely similar case in Mozambique 

 and another in Fiji. Why have these species thus 

 suddenly become extinct? 



Snails, being great eaters, meet their just reward 

 in being eaten. The paludine forms are sought 

 after by all sorts of water-birds, particularly ducks 

 and rails; while some tropical thrushes and other 

 birds crush the shells of the land snails and extract 

 their juicy bodies. Few birds, however, will eat 

 the naked-bodied slugs; the slime sticks to their 

 beaks and soils their feathers ; but the ducks seem 



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