1902 Snails hi Winter '^'X, 



found buried quite deep in the earth. How little the texture 

 of the shell is able to compensate for old tribal feelings and 

 habits is well shown in the species I have mentioned. Cryp- 

 tomphalus, Tachea, and especially Cyclostoma, all have thick 

 shells, and the last named has a stout operculum as well ; 

 while Vitrina has the thinnest of shells, which, as a rule, 

 only covers a portion of its person. One of the most at- 

 tenuated coverings among English snails is that of a species, 

 Fruticicola fusca, which has acquired some fame for its 

 boldness in frosty weather. 



Space forbids of more than a brief consideration of some 

 of the points which are suggested by the behaviour of our 

 aquatic species in winter. The two factors which have 

 probably been chiefly instrumental in keeping the popula- 

 tion of our fresh-water system within such meagre limits 

 are the rapidity of the efferent currents to the sea, and 

 the variations of temperature to which small bodies of 

 water are subject, with their attendant dangers of dessi- 

 cation on the one hand and freezing on the other. Were 

 it not for that most convenient property of water which 

 results in an ice-film being first formed on the surface, 

 animal life in many ponds would in all likelihood be re- 

 duced almost to nothing. Records are abundantly present 

 in the literature of the subject showing that snails may 

 be frozen in a solid mass of ice for days or even weeks, and 

 yet recover and live when liberated by a thaw. Whether 

 in these cases the body of the animal has been actually per- 

 meated by an ice mass is, I think, somewhat doubtful. That 

 soft tissues could endure the cutting and disruptive effects 

 of the formation of a mass of ice crystals without suffering 

 some permanent damage seems improbable ; and in a good 

 many cases it has been shown that animals so enclosed 

 in a block of ice are in reality immediately surrounded by a 

 narrow liquid zone. The difficulty in believing that com- 

 plete freezing may be followed by permanent recovery, lies 

 not so much in the low temperature as in the mechanical 

 conditions to which the animal is subjected. 



Many of our water snails bury themselves in the mud at 

 the bottom during cold weather ; but one can usually find a 

 fair number in a lethargic state moving about in the upper 



VOL. I. — NO. I. c 



