176 Gaspard on Helix Ponialia. 



of the atmosphere. Thus it took place in twenty-one days over 

 my fire-place, where the constant temperature was about 20° R. 

 (77 Fahr.) as also in the garden in summer where the thermometer 

 was at 28° (95 F.) in the day, and 10" (55 P\) in the night. 

 On the contrary, those eggs which were constantly exposed to 

 12° (60" F.) were not hatched till thirty-one days, and at 6° 

 to 8° (45° to 50° F.) not before forty-five days. Similar expe- 

 riments on the eggs of Frogs afforded analogous results. 



1 am certain that those of Snails are not developed, but go on io 

 putrifaction, either when placed in water, or in a stagnant damp 

 atmosphere, under a vessel inverted over water. A few days be- 

 fore they are hatched, the eggs become hard, opake and white like 

 chalk, sometimes on one half, at others over three quarters, or 

 over the whole globe ', at length the little animal open with its 

 teeth the white calcareous envelope, and comes forth with its soft 

 tender shell, consisting only of one volution and a half, having its 

 four tentacula, two of which are furnished with the black point ; 

 and its heart may be seen beating through the shell. If this little 

 shell be thrown into an acid, even before it has left the egg, it is 

 dissolved with eff'ervescence. 



The animal, at its first exclusion, lives only on the pellicle of the 

 egg, the whole of which is eaten. It is appropriated to it, like 

 the milk to the young of Quadrupeds ; the yelk of the egg to those 

 of Birds, of Chelonian and Saurian reptiles ; the glaire of the egg 

 to Batrachian reptiles, &c. In fact, this pellicle consisting of car- 

 bonate of lime, united with an animal substance, is necessary to 

 produce the calcareous secretion of the mantle, and to consolidate 

 the shell, at present too soft to be exposed without injury. When 

 this envelope is wholly eaten, the little snail is nourished only by 

 the moio or less vegetable soil which surrounds it, and in which it 

 continues to find materials for the secretion of the shell. It re- 

 mains thus concealed under ground in the nest for more than a 

 month, when it comes forth, feeds on vegetable matters, and es- 

 pecially on their decayed remains, and even yet returning fre- 

 quently to an earthy aliment Its increase i^ rapid during the 

 first year, and it has acquired considerable size by October, when. 

 it hibernates and forms its operculum for the first time. I am not 

 acquainted at what period it begins to propagate. 



