MOLLUSC A. 



229 



The female of the Paper Nautilus has the well-known 

 shell, but the male is without. The shell is simple, 

 not chambered as in the Pearly Nautilus, though an 



Fia;. 79. — Pearly Nautilus (Jf, pom-pilius), a surviving formof Tetral)rancliiat& 

 Cephalopod ; shown in socfcion, to exhibit the air-chambers of the shell. 



allied species has chambers. The male is much like 

 an Octopus. Like all the male Cuttle-fishes, it has 

 one of its arms converted into a sexual organ, which 

 is called a hectocotylus. In the Paper Nautilus, and 

 some other forms, this breaks off, and is left in the 

 shell of the female. 



