HODGSON ON HELIX, AND PERFOKATED LIMESTONE. 43 
Helices, and 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. 
Finding 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 through 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. Flake 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 otf 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channeled or spoon-shaped, and in this form is withdrawn, the con- 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 
