412 THE OCEAN WORLD. 
gizzard, with two accessary pockets, one of which 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 
2 
Fig. mgs depilans Fig. 180.—Aplysia inca (D’Orbigny). ee esi of 
inn). plysia 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 (Linnzus). 
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 
