THE BORING SNAIL. 
55 
washed away. If the snail be removed and placed on litmus 
paper, the ruddy violet colour which at once tinges the paper 
shows that there is acid of some kind, and if the paper be 
applied to the spot whence the snail has been taken, the same 
results follow. It is a remarkable fact that although the snail 
leaves the usual slimy marks of its progress when crawling in 
the summer time, no mucus is perceptible on the approach of 
winter. When the cold months come found, the Boring Snail 
leaves its food and attaches itself to the rock, remaining in the 
same spot until summer approaches. During this time, the 
portion of rock to which it clings is- worked away, and the 
stone around the excavation is impregnated with a greasy 
matter which soon dries up after the admission of the atmo- 
sphere. In a letter to me, dated October 14th, 1863, Mr. 
Hancock remarks that the rock at Monte Pellegrino in Sicily, 
which is crystalline and hard as marble, is perforated by the 
same snail and in the same manner. I may here mention that 
the stone of the Bois des Roches is that of which- the column at 
Boulogne is built, which has retained its sharpness of outline 
after exposure to wind and weather for nearly sixty years. It 
is therefore called marbre Napoleon . Mr. Hancock proceeds 
to say, 4 The following are a few of the peculiarities which I 
have not mentioned in my letter in the Field : 
4 1 st. There is no instance at Bois des Roches, of a tunnel 
being formed on the horizontal surface of a rock, or on the 
sides facing the south and south-east. They are always on the 
sides facing the north or north-east. 
4 2nd. The snail forms no epiphragm. 
[The 4 epiphragm ’ is the barrier of hardened mucus with 
which snails mostly close the entrance of their shells. There 
are generally several epiphragms in each shell.] 
4 3rd. Though during the summer it leaves behind it the 
usual slimy mucus track ; in the winter on returning to the 
rocks no track is perceptible except the corrosion of the rock 
by frequent passage. This would seem to point to a system of 
secreting organs for the acid, separate from that for the mucus. 
4 4th. Contrary to the usual habits of burrowing molluscs, who 
