166 A COURSE ON ZOOLOGY. 



bag," that produces a black liquid from which the 

 artists' color, sepia, was formerly prepared. 



Cephalopods have been classified in two groups, ac- 

 cording to the number of gills. The dibranchial are 

 those that have two gills, like the argonaut, the sepia, 

 and the squid. The tetrabranchial have four gills, arid are 

 now represented only by the genus nautilus, which was 



FIG. 



CUTTLE-FISH (Sepia officinalis), swimming and at rest. 



very abundant in geologic ages ; the ammonites, now 

 found only as fossils, belong to this group. 



Cephalopods all live in the sea ; we can mention only 

 the squids and the cuttle-fish. 



Squids are abundant on the Atlantic coast. By the 

 aid of their eight strong arms, which are furnished with 

 suckers, they swim in the water or climb over the rocks. 

 Those which are seen usually are rather small, but out 



