HABITS AND PROPERTIES. 51 



lation becomes slow, the pulsations of the heart, which 

 in the season of activity vary from forty to sixty in a 

 minute, according to the temperature of the air, decrease 

 in frequency and strength, until they at length become 

 imperceptible. The other ftmctions of the body cease, 

 and a state of torpidity succeeds, which is internipted 

 only by the reviving heat of the next spring's sun. 

 During the months of April or May, on the accession of 

 the first warm weather of the season, the animal breaks 

 down and devours the membranous partitions, and comes 

 forth to participate in the warmth and freshness of the 

 season. At first it is. weak and inactive, but recoveiing 

 in a short time its appetite, resumes its foinner activity. 



The season of hybernation continues from four to six 

 months. The final cause of this extraordinary condition 

 is undoubtedly to enable the animal to resist successfully 

 the extreme reduction of temperature, and to survive 

 through the long period when it must, in northern cli- 

 mates at least, be entirely destitute of its usual food. 

 With a view to the first purpose, a place of shelter is 

 provided, and the aperture of the shell is hermetically 

 sealed by the epiphragm or the hibernaculum ; for the 

 second, the state of torpor is adopted, during which the 

 functions of digestion, respiration, and circulation being 

 suspended, and all the secretions and excretions having 

 ceased, there is no drain upon the strength and vitaUty 

 of the animal, and no exhaustion of its forces. Hence 

 it comes forth, at the end of the period, in much the same 

 condition in wliich it commenced it, and resumes almost 



