72 



ZOOLOGY. 



ribbon." Familiar examples of the class are the sea-snails, 

 the sea-slugs, and the genuine air-breathing snails and 

 slugs. 



In the shell-less or Nudibranch mollusks, such as the 



Fio. 81.— ^Eo!is, a Nudi- 

 branch; enlarged twice. 



Fig. 83.— P/n/.sa heterostropha. Com- 

 mon pond-snail. After Morse. 



.Eolis and Doris and allied forms, the gills are arranged in 

 bunches on the back, as seen in Fig. 81, JEolis pilata, a 

 common species on the coast of New England. In Doris 

 (Fig. 82) they are confined to a circle of pinnate gills on 

 the hinder part of the back. 



FlQ. 84.- 



-Limnosus elodcs, a common pond snail showing its variations. 

 Morse 



After 



The air-breathing mollusks (PulDtoitata) are represented 

 by the pond-snails, Pliysa (Fig. 83) and Livmcetis (Fig. 

 84), and the land-snails and slugs. Fig. 85 represents 

 a slug suspended by a slimy thread from a twig. 



