HELIX, 131 



more thickly clad congeners were hibernating below 

 the surface. The temperature fell considerably during 

 the next few days, and I visited the spot repeatedly 

 to find, if possible, the limit to the endurance of this 

 slender mollusc. The following notes -from my 

 memoranda at the time will best show the result. 

 Dec. 26th, the thermometer at early morning registered 

 26° and the herbage was fringed with sparkling 

 crystals of rime, notwithstanding which the little 

 creatures were abroad and lively, crawling up the 

 blades of the Great Hairy Woodrush (Luzula syhaticd) 

 not simply indifferent to a temperature which be- 

 numbed my own extremities, but positively agile. 

 Dec. 27th, min. temp. 28^ Dec. 28th, min. temp. 28°: 

 this morning H. fiisca still about and vigorous. 

 Dec. 29th, temp. 25°. Dec. 30th, temp. 32'^: after an 

 hour's search I found only one individual. Dec. 31st, 

 temp. 26° : none to be seen. The frost continued 

 without intermission throughout the first week of the 

 new year, during which time on the occasion of two 

 visits to the same and neighbouring spots I failed to 

 find it about, nor could I discover any at the roots of 

 the Luzula. Jan. 9th, milder : H. fiisca again abroad, 

 and more abundantly on the lOth. It appears then 

 that a continuance of a temperature below freezing 

 point for six successive days was necessary to drive to 

 its retreat a mollusc protected by a .shell so thin as 

 to be almost membranous, and that, on the slightest 

 return to warmer weather, the circulation of the 

 animal sufficiently increased to enable it to resume 

 activity." 



Moquin-Tandon says that the members of this 



K 2 



