GASTEEOPODA. 



393 



tained in the branchial shield. In Fig. 182 we have the small and 

 thin cartilaginous shell which exists in the interior of the animal. 



Fig. 180. Aplysia depilaus 

 (Lin). 



Fig. 181. Aplysia inca (D'Orbigny). 



Fig. 182. Shell of 

 Aplysia inca. 



The Aplysise are found nearly in every region of the globe, not only 

 upon the shores of the Continent, but on every island shore. They 

 commonly inhabit sandy and muddy shores of small depths, or even 

 the rocky recesses, or under shelter of the stones which have fallen 

 from the cliffs. Their eggs consist of those long filaments which are 

 discharged in immense numbers, and which fishermen call sea-worms. 



They feed upon certain algae, with which the bottom of the sea is 

 covered ; but they eat, also, small marine animals, such as the naked 

 molluscs, annelids, and crustaceans. 



We are the less astonished to see the Aplysiee so gluttonous when 

 we learn how liberally Nature has accorded to them organs of masti- 

 cation, trituration, and digestion. Their mouth is formed of thick 

 and muscular lips ; a very long oesophagus or gullet succeeds, and 

 this oesophagus does not communicate with a single stomach, but 

 with four one enormous membranous crop, an exceedingly muscular 

 gizzard, with two accessary pockets, one of which terminates in the 

 form of a 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 

 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 Aplysiae. They have 

 a well-developed shell, the form of which is elegant ; they are delicate 

 in structure ; their brilliant colours, consisting of red, black, or white 



