CEPHALOPODA. 191 



maries, and Paper Nautilus, and they are characterized by 

 being almost invariably destitute of any external shell ; by 

 never having more than eight or ten arms, which are always 

 furnished with suckers ; by having only two gills, which are 

 provided with " branchial hearts ; " by the possession of an 

 " ink-bag ; " and by the fact that the " funnel " forms a com- 

 plete tube. They are divided into two sections Octopoda 

 and Decapoda according as they have only eight arms, or 

 eight arms with two additional longer processes or "tentacles " 

 (Fig. 89). Among the Octopoda are the Paper Nautilus and 

 the Poulpes ( Octopus). The Paper Nautilus is found in the 

 warmer seas of various parts of the world, generally floating 

 at the surface. The two sexes differ, as already said, greatly 

 in external appearance. The female (Fig. 90) inhabits a beau- 



FIG. 90. Argonauta argo, the Paper Nautilus, female. The animal is represented in its 

 shell, but the webbed dorsal arms are separated from the shell which they secrete, and 

 which they ordinarily embrace. 



tiful one-chambered shell, which is secreted by the webbed ex- 

 tremities of two of the dorsal arms. The shell is not in any 

 way attached to the body of the animal, but the webbed arms 

 are turned backward, and the animal sits in the shell with the 



