116 HOMES WITHOUT HANDS. 



leaves its food and attaches itself to the rock, remaining in the 

 same spot until summer approaches. During this time, the por- 

 tion 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 atmosphere. 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 man- 

 ner. I may here mention that the stone of the Bois de Eoches 

 is that of which the column at Boulogne is built, which has re- 

 tained its sharpness of outline after exposure to wind and weath- 

 er for nearly sixty years. It is therefore called marbre Napoleon. 

 Mr. Hancock proceeds to say, "The following are a few of the pe- 

 culiarities which I have not mentioned in my letter in the Field: 



" 1st. There is no instance at Bois de Roches of a tunnel being 

 formed on the horizontal surface of a rock, or on the sides facing 

 the south and southeast. They are always on the sides facing 

 the north or northeast. 



"2d. The snail forms no epiphragm." 



[The " epiphragm" is the barrier of hardened mucus with 

 which snails mostly close the entrance of their shells. There are 

 generally several in each shell.] 



" 3d. 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 or- 

 gans for the acid, separate from that for the mucus. 



"4th. Contrary to the usual habits of burrowing mollusks, who 

 generally have a bed of muddy matter between their shells and 

 the walls of their dwelling, the Helix saxicava keeps his tunnel 

 perfectly clean and neat. 



" 5th. When the liquor alluded to as forming a fatty aureole 

 round the tunnel penetrates into pre-existing clefts in the rock, it 

 provokes the growth of a microscopic lichen, which also grows in 

 the tunnels in places after the liquor has evaporated. 



"6th. The tunnels of the Helix saxicava are always irregular, 

 bearing no relation to the size or shape of the excavators, where- 

 as, in other excavating mollusks, the shape of the hole always 

 bears some relation to its occupant, and also the excavations are 

 alike for all animals of the same species." 



There is an opinion that the gastric juice secreted in the stom- 



