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NATURE STUDY 



Of the smaller air-breathing pond snails, Physa is a 

 good example. 



Paludina is a gill-breathing poiid snail. The water is 

 conveyed to the gills by a tube on the right, and is then 

 forced out of the tube on the left. The proboscis is well 

 developed. The eyes at the base of the tentacles are borne 

 on small projections. The young are brought forth alive, 



Ehtrance.. 

 10 GiLtj 



OPERCULUM. 



Paludina, a gilJ-breather. 



the eggs developing inside of the mother. Only the 

 gill-breathing forms have an operculum. " Eye stones " 

 are small lime opercula. Land snails have two pairs 

 of tentacles. On the longer of these are borne the eyes, 

 which can be invaginated. Land snails are found wher- 

 ever there is lime and moisture. They both breathe and 

 protect themselves from cold and dryness, like Limnea. 

 To this genus (Helix) belong the edible snails. 



