AIR-BREATHING MOLLUSKS. 



73 



The common snail^, Helix alholalris, is a type of the aii-- 

 breathing mollusks. Fig. 86 represents this snail of natu- 

 ral size, in its shell. The opening to the lung is seen at a, 

 and at B is represented the heart and lung of the garden 

 slug [Limaxfiavus). 



The eggs of the pond-snails are laid in transparent cap- 

 sules attached to submerged leaves, etc. 

 Those of Physa heterostropha are laid in I 

 the early spring, and three or four weeks | 

 later from fifty to sixty embryos with 

 well-formed shells may be found in the | 

 capsule. 



The eggs of Limncsus are laid late ir 

 the spring in capsules containing one oi 

 two eggs, and surrounded by a mass o] 

 jelly. 



Land£ggpls and slugs lay their eggs 



loose opmei" damp leaves and stones, and fiq. 85.— siug; natural 

 develOpiuent is direct, the young snail ^'''''• 



hatching in the form of the adult. 



Various shells, such as Marginella, Turbinella, etc., are 



Fig. 86.— .4, common .snail, natural size; B, the heart and lung. 



strung in bracelets and armlets by savages. Cyprma mo- 

 neta, the cowry (Fig. 87), is used for money, and other 

 shells are worked into various shapes for wampum or abo- 



