AIR-BREATHING GASTEROPODS. 



shell-less except when very young. Eolis and Tritonia have 

 been heard to make audible sounds. The eggs of Doris 



FIG. 68. Naked-gilled mollusca, commonly called sea-slugs. D, Doris 

 pilosa ; E, Eolis coronata ; f, foot ; g, breathing-gills ; /, tentacles. 



are incased in a ribbon and rolled up like a watch-spring ; 

 360,000 young are often produced, that are at first free 

 swimmers. 



AIR-BREATHING GASTEROPODS (Pulmonata). 



General Characteristics, Mollusks possessing a single 

 lung, a chamber on the right side of the body near the 

 head, lined with a membrane containing blood-vessels. 

 The cavity is closed 

 by a valve. The shell, 

 when present, is gen- 

 erally thin and deli- 

 cate, and often highly 

 colored. 



Pond -Snails 



, . FIG. 69. #, egg capsule of a fresh-water 



\L,imn<Zt(l(E) . - snail . ^ c ^ eggs highly magnified, show- 



ire the common pond- ing the young snail, (After Morse.) 



