BURROWING MOLLUSKS. 115 



them. Mr. Hancock, who has lately reopened in the columns of 

 the Field newspaper a controversy respecting these snails, which 

 was initiated in 1839, is of opinion that the snails really form the 

 hole, and that they burrow at the average rate of half an inch 

 per annum. The late Dean Buckland was of the same opinion. 

 Other naturalists, however, think that the holes were originally 

 excavated by pholades and other marine mollusks when the 

 rocks in question formed part of the ocean bed, and that the 

 snails merely inhabit the ready-formed holes. Mr. Pinkerton up- 

 holds this opinion, and states that at least three other species of 

 helix possess similar habits, the garden and the banded snail be- 

 ing among the number. 



I have compared the burrows of the mollusk, which we will 

 call the Boring Snail, with those of the pholas and lithodomus, 

 both of which will be presently described, and find that there is 

 no resemblance in their forms, the shape and direction of the 

 holes being evidently caused by an animal of no great length 

 in proportion to its width. In my own specimen, every hole is 

 contracted at irregular intervals, forming a succession of round- 

 ed hollows. If we return to our lump of putty, we may form 

 the holes made by the thumb into a very good imitation of 

 those in which the Boring Snail lives. After the thumb has 

 been pushed into the putty and well twisted round, put in the 

 forefinger as far as the first joint and turn it round so as to 

 make a rounded hollow. Push the finger into the hole as far 

 as the second joint, and repeat the process. Now introduce the 

 whole of the finger, enlarge the extremity of the hole and round 

 it carefully, when there will be a very correct representation of 

 the tunnel formed in the rock. 



Granting that the snail really does form the burrow, we have 

 still to discover the mode of working. Mr. Hancock says that 

 it must do so by means of an acid secretion proceeding from 

 the foot, which corrodes the rock and renders it easy to be 

 washed away. If the snail be removed and placed on litmus 

 paper, the ruddy violet color which at once tinges the paper 

 shows that there is acid of some kind, and if the paper be ap- 

 plied to the spot whence the snail has been taken, the same re- 

 sults 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 round, the Boring Snail 



