x MOLLUSC A 133 



structure is not present in the young snail, being only formed 

 as it approaches its maturity. Clausilia has four tentacles, 

 but the two lower ones are very short. 



The chief enemies of snails are the various 

 birds which feed on them ' Particularly the thrush, 

 which often has a special table-stone on which 

 it smashes successive victims, holding them by the lip of the 

 shell, and breaking the spire on the stone. 



Gardeners also are the snails' constant enemies, on account 

 of the very great damage the latter do in a garden. For whilst 

 most wild plants have acquired some more or less adequate 

 defence against the ravages of snails either by the forma- 

 tion of a surface covering of hairs, or by a secretion of silica 

 or calcium carbonate which hardens the external tissues, or 

 by the secretion of some such substance as tannin cultivated 

 plants have, as a rule, no such protection, and so fall easy 

 victims to hungry snails. It is interesting to test the value 

 of the various protective contrivances by giving snails a 

 variety of apparently protected and unprotected plants to 

 eat, and noting the results. 



Snails have been cultivated as an article of 



Snail? * ood even at so eai 'ty a date as ^ B.C., and were 

 considered a great delicacy by the Romans. Prob- 

 ably they were eaten also by the cave men of the Stone 

 Age, for masses of Helix shells are found in their caves. 

 Snail gardens are still to be seen in many parts of France 

 and Spain. Helix pomatia, the Apple Snail, which is common 

 in vineyards, is specially valued as an article of food, but 

 several other species are also eaten. 



Various concoctions of snails used to be made as remedies 

 for many kinds of disease, especially for consumption, and 

 the idea of their healing power in this disease still lingers in 

 some parts of the country. 



The shell of the Almond Whelk (Fusus antiquus) often serves 

 the fishermen of the Shetlands for a lamp. It is suspended by 

 a string, filled with fish-oil, and provided with a cotton wick. 

 Snails can withstand considerable extremes of 

 of Siiails 6 co ^ d and nea tj and even drought, owing to the 



epiphragm or operculum, with which they prevent 

 the complete loss of moisture from the body when they enter 

 a state of torpor. 



