HIBERNATION 333 



with the Winter, it keeps in hiding when it is not alert 

 enough to do itself justice, and it gives its body a long rest. 



A survey of the Winter-sleepers seems to show that the 

 life-saving reaction must have arisen by the natural selection 

 of variants in the direction of the hibernating habit. That 

 is to say, those that were constitutionally able to assume 

 a comatose condition when the cold weather set in, yet 

 without endangering their lives, were the survivors. On 

 this view we can understand how it is that the hibernating 

 habit is definitely related to the other habits of the creature 

 for instance, why it should occur in the land-shrew, but 

 not in the water-shrew. It is an adaptive character. 



But although the hibernating habit may be exhibited 

 by one species of mouse and not by another, being in no 

 way wrapped up with a special kind of constitution, we 

 must recognise that it means in the higher reaches of life 

 a somewhat delicate adjustment of an ordinary constitu- 

 tion. When a mammal whose constitution is not adjusted 

 to hibernation falls into a cold -coma it is not likely to 

 awaken. This is familiar to us in the case of man and his 

 stock. 



WINTER SLEEP OF COLD-BLOODED ANIMALS 



Many cold-blooded animals, which take on the 

 temperature of the surrounding world, pass into a leth- 

 argic state in Autumn. Professor Semper says that they 

 are " lulled to sleep by the falling temperature/' but it 

 must be understood that their condition is very different 

 from sleep as we know it. Often it seems more like 

 " Sleep's twin-sister, Death," so thorough is the stoppage 

 of all activity. The common edible snail, Helix pomatia, 

 closes the door of its shell with a hard lid of lime and slime, 

 and keeps the door shut for four months. All this time 

 it is fasting ; its respiration must be extremely sluggish 



