XIV INTRODUCTION. 



The phenomena of hibernation are amongst the most re- 

 markable and interesting which occur in the history of ani- 

 mals. That the cold-blooded creatures of which we are 

 now treating, with their limited respiration and circula- 

 tion, their entire dependence upon external heat to carry 

 on their functions, and the consequent diminution of all 

 their powers, and of their expenditure also, during a low 

 degree of external temperature, should be able to sustain 

 life for an almost indefinite period, under peculiar circum- 

 stances, is not, perhaps, so surprising. But this simple 

 torpidity is very different from that true hibernation to 

 which many of the warm-blooded animals are liable. The 

 bats, the squirrel, the dormouse, the marmots, and many 

 others, may be cited as examples. It is sufficient in 

 reference to the present class to observe, that in temperate 

 or cool climates, the whole of them retire during the winter 

 to some place of concealment ; the land Tortoises to exca- 

 vations which they often dig for themselves ; the fresh- 

 water Tortoises to holes in the muddy banks, or to the 

 mud at the bottom, of their native lakes or rivers : the 

 Lizards and Serpents to holes in trees, under stones, 

 beneath dead leaves, or in similar hiding-places, where 

 many species, especially of the latter order, congregate 

 in large numbers, and are found closely entwined together. 

 Here they pass the winter in a state of almost lifeless re- 

 pose, the functions of life so nearly suspended, that none 

 of the external signs of its existence are visible. The 

 circulation is extremely slow, the respiration apparently 

 altogether stopped, digestion absolutely suspended. The 

 return of the genial warmth of spring calls them again into 

 action. The circulation is restored, the blood is again 

 fitted for its various offices by the return of regular respi- 

 ration, the functions of the digestive organs are again 



