INTRODUCTION. Xlll 



sphere ; and even under the most favourable circumstances is 

 extremely slow. Many Serpents are more than a fortnight 

 after taking their food before the undigested remains are 

 voided, during which period they usually fast. If the tem- 

 perature in which they are placed be very low, it is greatly 

 retarded, and during hibernation it ceases altogether ; for I 

 have known a Tortoise which had fed largely upon grass im- 

 mediately before it became torpid, retain the grass un- 

 changed in the stomach during the whole of the winter, so 

 that on opening the body after its death, which took place 

 immediately on its awaking in the spring, and before it had 

 any access to food, the stomach was found filled with a large 

 quantity of grass wholly undigested. 



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 circulation, their 

 entire dependence upon external heat to carry on their func- 

 tions, 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 in- 

 definite period, under peculiar circumstances, 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 dor- 

 mouse, 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 excavations which they often dig for them- 

 selves ; 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, 



