412 



THE OCEAN WORLD. 



gizzard, with two accessary pockets, one of w^hich terminates in the 

 form of sac. The gizzard has thick walls, and is furnished on the 

 internal wall with cartilaginous quadrangular pyramids, the summits 

 of which intertwine. This apparatus is intended to bruise the food 



Fig. 179. — Aplysia depilans 

 (Linn). 



Fig iSo. — Aplysia inca (D'Orbigny). 



Fig. iSi.--Shell of 

 Aplysia inca. 



when it reaches the third stomach. It is also armed with little 

 hooks, the curvature of which is directed towards the entrance of the 



gizzard. 



The genus Bulla differs materially from the genus Aplysia. 

 The species have a well-developed shell, the form of which is elegant 



Figs. 182 and 183. — Bulla ampulla (Linnseus). 



and delicate in structure ; their brilliant colours, consisting of red, 

 black, or white bands, separated by many varied tints, cause these 

 little shells to be much sought after for ornamental collections. The 

 shell itself is oval or globulous, rolled up in a scroll, smooth, spotted, 

 very thin and fragile, with a concave spire, umbilicate, open in all its 

 length, with a straight, wide, and cutting edge. The gills of the 

 animal are placed upon the back, a little to the right and behind, but 



