302 



LOWER INVERTEBRATES. 



the outside of the tentacles near their junction with the head. The shells are mostly 

 small, and j^ossess but little interest ; a large proportion are fossil, ranging from the 

 carboniferous to the present time. 



The Bullion embraces much larger forms, in which the ventricose 

 -^^ shell is coiled in a spiral in which the sjiire is internal. The shell, in 

 ^ '^Sm niany forms, is spirally banded or spotted, and is more or less concealed 

 Ww ''-^ ^^^^ mantle and epipodia. I^h-e lingual ribbon bears one median and 

 nianv lateral teeth. In Bulla the eves are sessile on the middle of the 

 — '^ frontal fold formed by the united bases of the tentacles. The species 

 FiG.343.— ronm- fvequent sandy and muddy bottoms near the shore, even going into 

 brackish water. At the retreat of the tide they bui-row into tlie mud or 

 hide themselves beneath masses of seaweed. On our east coast is found H. solitaria, 

 a brownish spotteil form. Cylichna, which possibly deserves family rank, is repre- 

 sented on our shores by several small cylindrical shells which frequent slightly deeper 

 water than the Bullas. They move very slowly. Hambiea may be readily separated 

 from Bulla l)v the lack of color in the shell. 



In the PiiiLiNiD^E the bases of the tentacles are united to form a broad cephalic 

 disc. The shell, which is covered by the mantle and epipodia, is shaped like that of 

 Bulla, but scarcely forms a single whorl ; in some it is internal and in others external. 

 Eyes may be present or absent. The species are found in water of moderate depth, 

 many species of Philine frequenting the shallow water along the shores. 



The Aplysiid^ embraces slug-like forms known in popular parlance as 'sea- 

 hares.' The shell is small or wanting, and when present is covered by the mantle. 

 The stomach is armed with hardened teeth which ])lay no unim|iortant part in j)repar- 

 ing the food for digestion. The animals feed principally on other molluscs, especially 

 on species of y\cera (one of the Bullidae). Aplysia., the principal genus, has a pointed 

 oval shell, and the e])ipodia are extended in swimming. In one species {A. camelus) 

 numerous small glands are foimd beneath the free edge of the mantle which secrete 

 the purple for which these animals were celebr.ated among the ancients. Near the 

 base of the gill is tlie outlet of a gland, the secretion of which is said to be poisonous, 

 but whether any of the sea-hares have the toxic effects attributed to them, or even 

 have any poisonous qualities, is yet to be determined. Certain it is that all of the 

 group are not ]ioisonous, for one S])ecies forms an article of diet among the South 

 Sea Islands. Some of the European species have a very nauseous smell. 



