TORPIDITY OF REPTILES. ' 141 



The labour of forming the nicely adapted exca- 

 vation or hybernaculum occupies two or three 

 days, but the whole of October is taken up by the 

 process of closing the shell. About the beginning 

 of April, revivification takes place. The mode 

 of escape from confinement is simple. The air 

 which is contained in the different opercular 

 cells is again inspired, each membranous par- 

 tition being broken in turn by the pressure of 

 the muscular foot projected through the mantle. 

 When it arrives at the outer calcareous expan- 

 sion, the animal making a last effort bursts and 

 detaches its most obtuse angle. Then insi- 

 nuating by little and little the edge of the foot 

 between the- shell and the operculum, it forces 

 the latter off, or breaks it away. 



How far our fresh water mollusks enter into 

 a state of hybernation is not very palpable ; 

 certainly most, if not all, bury themselves during 

 the winter in the oozy mud of rivers, gently- 

 flowing ditches, or drainage courses, lakes, or 

 ponds, and probably become torpid. As it 

 regards marine mollusks, we know little or 

 nothing. It may here be remarked, that in 

 dry weather, even during summer, our terrestrial 

 shelled snails throw a thin operculum over the 

 mouth of their shell, and attach themselves to 

 any convenient substance, and thus appear to 

 become dormant. From this state they are 

 roused by the first warm shower, and creep 

 abroad in the enjoyment of their animal powers. 

 Warm, humid, showery weather, and the 

 approach of eventide, appear to the snail and the 



