50 HELICIDyE. 



umbilicus being minute, but open. Its growth is rapid, 

 and it has usually increased in magnitude three or four 

 times, before the close of the first year. 



In the month of October, or at the epoch of the first 

 frost, the snail ceases to feed, becomes inactive, and fixes 

 itself to the under surface of the substance by which it 

 is sheltered, or partially burrows in the soil, and with the 

 aperture of the shell upward, disposes itself for its annual 

 sleep or hibernation. Withdrawing into the shell, it 

 forms over the aperture a membranous covering, con- 

 sisting of a thin, semi-transparent mixture of lime mu- 

 cus or gelatine, secreted from the collar of the animal. 

 This membrane is called the epipliragm. It is formed in 

 this manner. The animal being withdrawn into the shell, 

 the collar is brought to a level with the aperture, and a 

 quantity of mucus is poured out from it and covers it. A 

 small quantity of air is then emitted from the respiratory 

 foramen, which detaches the mucus from the surface of 

 the collar, and projects it in a convex form, like a bubble. 

 At the same moment, the animal retreats further into the 

 shell, leaving a vacuum between itself and the membrane, 

 which is consequently pressed back by the external air to a 

 level with the aperture, or even farther, so as to form a 

 concave surface, where, having become desiccated and 

 hard, it remains fixed. These operations are nearly sim- 

 ultaneous, and occupy but an instant. As the weather 

 becomes colder the animal retires further into the shell, 

 and makes another septum, and so on, until there are 

 sometimes as many as six of these partitions. The circu- 



