THE GREAT GRAY SLUG AND THE POND-SNAIL. 603 



then sets about making its winter habitation. This process is very 

 curious, and is thus described by Mr. Bell : 



"A large quantity of very viscid mucus is secreted on the under 

 surface of the foot, to which a layer of earth or dead leaves adheres ; 

 this is turned on one side, and, a fresh secretion being thrown out, the 

 layer of earth mixed with mucus is left. The animal then takes 

 another layer of earth on the bottom of the foot, turns it also to the 

 part where he intends to form the wall of his habitation, and leaves it 

 in the same manner, repeating the process until the cavity is sufficiently 

 large, and thus making the sides smooth, even, and compact. In form- 

 ing the dome or arch of the chamber a similar method is used, the 

 foot collecting on its under surface a quantity of earth, and the animal, 

 turning it upward, leaves it by throwing out fresh mucus ; and this is 

 repeated until a perfect roof is formed. 



" As I have very often watched this curious process, I am certain of 

 the facts. On removing very carefully the portion of the roof soon 

 after its completion, I was enabled to see the formation of the opercu- 

 lum. In about an hour, or even less, the whole surface of the collar 

 of the mantle instantaneously pours out the calcareous secretion in 

 considerable quantity. 



" This is at first a fluid or thick cream, but very soon acquires 

 exactly the consistence of birdlime, being excessively adhesive and 

 tenacious, and in about an hour after it is poured out it is perfectly 

 solid." 



We now arrive at the great family of Limacidse, or Slugs, a race 

 of beings which many a gardener doubtless wishes extinct. 



In these creatures the foot and body are indistinguishable from each 

 other ; the head is retractile, and the whole creature can be gathered 

 into a short rounded mass, looking so like a pebble that it would escape 

 a casual glance. At the first view the Slugs appear to be destitute of 

 shell, but on a closer examination the shell is found upon the fore 

 part of the body, and either entirely or "partly buried beneath the 

 integuments. 



The Great Gray Slug is the largest of the British species, and 

 when furnished with abundant food on which it can fatten itself during 

 the night, and a secure hiding-place whither it can retreat during the 

 day, often attains an enormous size. 



The Water Snails are represented by the common Pond-snail, or 

 LiMNiEA. In all the members of this family the shell is thin, and 

 suflficiently capacious to contain the entire animal when it desires to 

 withdraw itself into its home. The aperture is simply rounded, with- 

 out notches or ridges, and the lip is sharp. 



It may be found plentifully in nearly all streams where the water is 

 not polluted and the current not very swift. I have generally found 



