76 MICHIGAN ACADEMY OF SCIENCE. 



minutes the slug was in the water resting on the bottom of the dish, and 

 contracted as in the preceding experiment. It is not certain wliether 

 the animal crawled doAvn into the water or simply fell in, having 

 loosened its hold on the glass. It seems probable that the former action 

 is what occurred, since the slug was found some distance from where 

 it would have been had it simply fallen into the water. At the end of 

 an hour, the temperature of the Avater registering -\- 2° C as before, 

 the dish was taken back into the warm room, and as before the slug 

 soon revived and eiawled out of the water. 



On account of a pressure of other work it was unfortunately impos- 

 sible to carry these experiments any farther at the time. The slug- 

 lived about two weeks, and since it was kept at room temperature all 

 the time after the experiments recorded above, never again went back 

 into the water. 



The most probable explanation of this curious behavior on the part of 

 a mollusc which in its general habit is terrestrial, seems to be that, 

 when it was in the water, the organism Avas in a stitfc of hihrrnatioii. 

 This hibernation was induced by the Ioav temperature, and Avliile in the 

 hibernating state the respiratory exchange became extremeh^ low, so 

 that the slug could exist practically as well in Avater as in air. When, 

 howeA^er, the temperature Avas raised the animal revived, i. e., came out 

 of the hibernating condition, and then craAvled out of the Avater as soon 

 as possible. An objection which has been raised against such an ex- 

 planation is that it does not seem probable that the organism could pass 

 so quickly from the normal into the hibernating state. There are, how- 

 ever, no detailed experimental results on this point and we do not know 

 how long it takes for the slug to pass from one state into the other 

 under any given conditions. From some obserA'ations of my own on 

 Afjriolimax and Hiicciiica 1 feel sure that these animals are able to pass 

 into a condition of hibernation in a comparatively short time after the 

 cessation of activity (in some cases less than fifteen minutes). So then, 

 in the absence of detailed evidence, this objection on the ground of the 

 too great rapidity of the change from the normal to the hibernating 

 condition required in the given explanation, does not ai)pear to be a 

 particularly strong one. 



There seems to be some biological significance in this sort of behavior 

 of an hibernating animal with reference to Avater. During the winter 

 months the temperature of the water at the bottom of a river or pond 

 is considerably highei* than that of the surface layer of the soil. Hence 

 an organism runs much less risk of being frozen to death Avhen at the 

 bottom of a body of water than Avheu simply beneath a stone or the 

 upper layers of the soil. 



This explanation of tlie observations is merely a tentative one and 

 may or may not be correct. I lio]ie to be able at some future time to 

 make the detailed study of the phenomenon Avhicli the case seems to 

 warrant. 



