334 THE BIOLOGY OF THE SEASONS 



through that calcareous wall ; its heart, even when the 

 shell is broken, is beating very feebly. This is far below the 

 level which we know in sleep. How much more is that 

 the case with, for instance, the pupae of butterflies and 

 other insects, in which the whole structure of the larva 

 has been broken down and is in process of slow recon- 

 struction. No doubt all these states are at different 

 levels on an inclined plane, but there is a great contrast 

 between the disorganised pupa, which sinks back sometimes 

 till it is practically a winter-egg that has to be hatched a 

 second time, and the comatose but quite intact snail. 

 There is another great contrast, between the comatose snail 

 and the sleeping dormouse. 



PHYSIOLOGY OF HIBERNATION 



The physiology of hibernation is still very incomplete, 

 but a few general statements may be ventured : 



1. It is very frequently the case that some store of re- 

 serve material exists within the animal which is consumed 

 during the hibernation, serving, for instance, to sustain 

 the animal heat. Thus a store of fat, accumulated when 

 food was abundant, may serve, as it were, to keep the 

 fire "in," though it cannot do much more. 



2. A second general statement may be ventured, that 

 hibernating animals show a very marked slackening of 

 all the vital functions. The heart beats feebly and ir- 

 regularly ; the breathing movements are " shallow and 

 infrequent, sometimes coming practically to a standstill " ; 

 there is no excretion from the kidneys, or next to none ; 

 the usual muscular reflexes are weak, and the senses are 

 not readily stimulated. In short, the whole metabolism 

 of the creature is at a very low ebb. 



3. Very significant is the fact that in hibernating 



