386 



SECTION A. TECTIBRANCHIATA. 



1003. The animals of this Section still show an approach to 

 that arrangement of the gills, which characterises the great bulk 

 of the Class ; these organs being concealed beneath a fold of 

 the mantle, in which a small shell is usually contained. They 

 are all marine ; and live chiefly on the shore, or on floating sea- 

 weeds. A very characteristic example of the group is the 



FIG. 674. APLY81A. 



Aplysia, commonly termed Sea-Hare, which is abundant on many 

 parts of our own coasts, and which forms the type of the family 

 APLYSIAD E. Its common name is probably derived from the 

 peculiar form of the superior pair of tentacula, which are flattened 

 and hollowed like the ears of a quadruped. The head has a 

 very distinct neck. The gills consist of leaflets arranged in a 

 complex form, and situated on the back beneath a fold of the 

 mantle, which also frequently incloses a flat horny shell. The 

 digestive apparatus is very complicated ; consisting of a mem- 



FIG. 675. BCLI^KA APERTA. FIG. 676. BULLA LIGNARIA (a): BVLLA AMPULLA (I). 



branous crop like that of Birds, a gizzard having cartilaginous 

 walls, and a third stomach beset with sharp hooks in its interior. 





