lie 



CLAMS, OYSTEK.S, AND MUSSELS 



foot (Fia;. 62). The head bears two feelers, or tentacles, 



Phj'sa lays its eggs in February or March, in bean-shaped, 

 transparent, gelatinous masses, on leaves or sticks in the 

 water. Lininfea lays fewer eggs in a mass, and lays them 

 later in the spring. 



Besides Linmica and Physa, the snails that belong to the 

 genera Planorbis and Paludina are commonl}' known as 

 "pond snails." The members of the former genus have 

 shells coiled in a flat spiral, like a roll of tape, and breathe 

 air directly, like Limntea. The members of the latter genus 

 have, generally, a longer and more pointed shell and breathe 

 by means of gills, much like an oyster. 



Helix. — The common garden snail will serve well as an 

 example of the genus Helix (Fig. 63). It has a horn-coloreil 



shell within which it 

 can contract the whole 

 body. It has two 

 eyes, one at the end 

 of each of the large 

 tentacles. It breathes 

 by means of a lung 

 which communicates 

 with the outside by an opening in the side of the snail's 

 neck that can be closed or opened at will. This snail lives 

 on plants. In France, some memliers of the genus, Helix, 

 somewhat larger than our own ganlen snail, are extensively 

 eaten as food. 



Slugs. — The.se ai-e snails that have no visible shell, — 

 in fact, some of them haA'e none at all. They usually feed 

 only in the night time, hence are not often seen. One, which 

 is sometimes found crawling along roads or walks, is known 



Fig. 63 



- Garden snail. 



