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‘Gill University are kept 
