A MANUAL OF AMERICAN LAND SHELLS. 11 



it remains fixed. These operations are nearly simultaneous, and occupy- 

 but an instant. As the weather becomes colder the animal retires 

 farther into the shell, and makes another septum, and so on, until 

 there are sometimes as many as six of these partitions. The circulation 

 becomes slow, the pulsations of the heart, which in the season of activ- 

 ity vary from forty to sixty in a minute, according to the temperature 

 of the air, decrease in frequency and strength, until they at length be- 

 come imperceptible. The other functions of the body cease, and a 

 state of torpidity succeeds, which is interrupted only by the reviving 

 heat of the next spring's sun. During the months of April or May, or 

 on the accession of the first warm weather of the season, the animal 

 breaks down and devours the membraneous partitions and comes forth 

 to participate in the warmth and freshness of the season. At first it 

 is weak and inactive, but, recovering in a short time its appetite, re- 

 sumes its former activity. 



The season of hibernation 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 climates 

 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 se- 

 cretions and excretions having ceased, there is no drain upon the 

 strength and vitality of the animal, and no exhaustion of its forces. 

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

 dition in which it commenced it, and resumes almost immediately its 

 usual functions and habits. So entire is the cessation of the function 

 of respiration that the air contained between the epiphragm and the 

 animal is found to be unchanged. The circulation, however, may be 

 partially restored by a small degree of heat, the warmth of the hand 

 being sufficient to stimulate the heart to action. 



In the portions of the country subject to long periods of drought the 

 same process is resorted to as a defense against want of moisture. In 

 this case the epiphragm is much thicker. In the genus Binneya it is 

 still more developed, in order to protect the parts of the animal incapa- 

 ble of being drawn within the small shell. 



The snails pass the greater part of their lives under dead leaves and 

 logs, under stones, or burrowing in the ground. They seldom come 



