to 



ice." Judging' l)y the Ihiekness of the ice from which the 

 animals were taken and from tlie climate of the country 

 (Far Eastern Russia) he thinks that tliese organisms 

 must have been subjected to - 20^. 



Weigmami (19;>6) attempted to determine the body 

 temperature of snails, and of Helix pomatia in particular, 

 during death by cold. For that purpose he used a thermo- 

 couple inserted through the shell. The surrounding air 

 temperature was lowered slowly to a minimum where it 

 stayed for several hours. He found that when the snails, 

 with or without operculum, were frozen and when their 

 body temperature dropped to -3° to -4°, they were al- 

 ways killed. Whether they were also killed at higher 

 temperatures (between - 2° and - 3°) when ice was formed 

 in them, w^e cannot ascertain from Weigmann's paper. 

 He states, p. 310, that none of the species examined with- 

 stood freezing ("ein Einfrieren iibersteht also keine der 

 untersuchten Arten") and, p. 306, that some animals sur- 

 vived freezing at -2° (''ein Einfrieren bis auf -2° iiber- 

 leben"). Besides, a freezing curve is given (fig. 1) for 

 an individual which is reported to have survived (table 1). 

 As to the difference between operculated and non-opercu- 

 lated animals, Weigmann observed that the former could 

 resist for 4 to 5 hours air temperatures down to - 6°, while 

 the latter were killed in 4^ hours at - 4°. The water snails 

 Limnaea and BytJiinia are given as having a higher lethal 

 temperature than the land snails, namely, - 1.5°. 



6. Arthropods. The action of low temperature on 

 arthropods has been the object of a very large number 

 of observations and of investigations. Several reviews 

 have been published, of which we shall mention two : that 

 of Bachmetjew (1901 and 1907), and that of Uvarov 

 (1901). The reader will find in the former a detailed his- 

 tory and compilation of the older works, and in the latter 

 a short compendium of the more important modern 

 contributions. 



Although the larvae and the adult arthropoda present 

 a widely different cold resistance, we shall treat them 

 together. 



