HODGSON ON HELIX, AND PERFORATED LIMESTONE. 43 



Helices, aud that the eroding action is performed by the foot, with 

 the aid of an acid secretion. 



Ever since I became familiar with the microscopic structure of 

 the tongue of Helix, etc., I have always believed that it was so con- 

 structed for purposes of abrasion, either of stone or other hard sub- 

 stances ; but I was not previously aware that the land -snails were, 

 any of them, supposed to form for themselves hollowed, hybernating 

 chambers in rocks. That they do consume the limestone no one 

 who has seen the above memoir can doubt ; the only thing not so 

 evident is the way it is done and the purpose for its being done. 



rinding some individuals of Helix aspersa under a stone in a 

 hybernating state, I had the stone and all carefully placed under a 

 bell-glass in a warm room, leaving sufficient space under the edge of 

 the glass for air. The following morning all had burst the epiphragm 

 and shifted their position. In another day they were all upon the 

 glass, in full activity, crawling about. On examining the under-side 

 of the head througli the bell-glass with a lens, no tongue was visible, 

 but on smearing the glass with the juices of bruised geranium leaves, 

 the tongue protruded itself, making strokes upon the glass at the 

 rate of about one in three or four seconds. I then scraped a piece 

 of limestone with a pen-knife upon a sheet of paper, and moistened 

 the scrapings into a paste with distilled water, and then smeared the 

 inside of the glass with the paper. The action of the tongue hitherto 

 had been sluggish and not continuous, but the instant the head 

 came in contact with the lime the action quickened. Make after 

 flake was removed from the glass and taken into the crescent-shaped 

 mouth. The tongue appeared to be used nearly in the same way as 

 that of the pond-snail when it is taking off the green film from the 

 sides of the aquarium ; that, however, is accompanied by a clear, 

 ringing sound, doubtless owing to the necessary force used. In 

 Helix the tongue is curved outwards and first pressed momentarily, 

 more or less flat, against the glass, the next instant it becomes 

 channeled or spoon-shaped, and in this form is withdrawn, the con- 

 cave side uppermost. I have no doubt, however, on a dry substance, 

 one not so slippery as glass, that the flat application would be pro- 

 longed, and more muscular force exerted, — indeed I have occasionally 

 observed a slight jerk of the head as the tongue left the glass, indi- 

 cating greater power of stroke. 



On subsequently trying Helix nemoralis, it swallowed the lime 

 with the same avidity, and both worked at it, with short intervals 

 of rest, for hours and day after day. In both species a little wave 

 of moisture is driven before the head, extending beyond it about 

 the fiftieth part of an inch ; but the tongue appears to be drier in 

 H nemoralis than in H aspersa, although I think the amount of 

 fluid varies in both. When the animal is merely gliding along, and 

 not using the tongue, a little bubble of fluid is constantly, at short 

 intervals, emitted from the mouth, which partially opens for the 

 purpose. I have repeatedly saturated scrips of litmus paper in this 



