108 ANIMAL INTELLIGENCE 



most active to their most sluggish condition is not 

 probably relatively greater than in the case of 

 mammals. 



All forms of profound winter (or summer) sleep are 

 protective, both of the individual and the species. 

 Manifestly amphibia, reptilia, and other groups of 

 the animal kingdom must have utterly vanished from 

 the face of the earth but for such a power to adapt to 

 conditions. Probably many individuals, if not some 

 entire groups, have, through^ more or less complete failure 

 to adapt, disappeared before this habit of the nervous 

 system and of the whole organism became perfect 

 enough. 



It is equally clear from the investigation given to 

 the subject that hibernation, like daily sleep, is not a 

 fixed and rigid thing, but just as it has been the result 

 of adaptation to the environment, by virtue of the 

 plasticity of function of all living cells, so the power to 

 modify still remains. 



It is possible to conceive of its being lost in certain 

 groups of animals indeed this phase of the subject has 

 been as much impressed on me as the other. Sleep, 

 hibernation, and all such states are not invariable, but 

 to a certain extent, so dependent on the surroundings 

 that as in the case of my last marmot, also of turtles 

 and frogs kept within doors there may be an omission 

 of that condition which is habitual under the normal 

 environment of the animal. 



I would like to emphasise these facts, for they seem 

 to me to throw great light on the evolution of function 

 at all events, and on those changes which may become 

 so great as to lead, we can hardly say to what, in the 

 lapse of time. 



For years I have had turtles, and especially frogs, 

 under observation during the winter months. Our 

 frogs for laboratory use at M'Grill University are kept 



