256 ELEMENTARY ZOOLOGY 



They are the most highly organized molluscan forms, and 

 their predaceous habits and the great size to which some 

 of them attain have given them distinction among the 

 fierce and dangerous creatures of the sea. They are all 

 strictly marine in habitat, and are all carnivorous. Most 

 of them have no shell, or where the shell is present it is 

 internal in all but a very few forms. The tentacle-like 

 arms or feet surrounding the mouth which occur in all the 

 Cephalopods are provided with sucking organs or suckers, 

 in some cases with a horny toothed rim. These long, 

 powerful, grasping, tentacular feet, with the suckers and 

 five hooks, are very effective means of securing prey, and 

 the pair of strong, sharp, cutting mandibles or beaks are 

 equally effective in tearing to pieces. The eyes of the 

 Cephalopods are almost as highly developed as those of 

 the vertebrates. They are unusually large and staring, 

 and add much to the terrifying appearance of the " devil- 

 fishes." Cephalopods have the power of quickly chang- 

 ing color, because of the presence in the skin of many 

 pigment-cells which can expand so as nearly to touch 

 each other, thus producing a uniform tint over the whole 

 body, or which can contract so as to destroy this uniformity 

 of color. There are several sets of these color-carrying 

 cells or chromatophores, each set of a color different from 

 the others. The purpose of this change of color is pro- 

 tective, the animal being thereby able to make its color 

 so harmonize with that of its immediate surroundings as 

 to become indistinguishable. 



There are two principal groups of Cephalopods, viz., 

 the Decapods and the Octopods. The Decapods, as their 

 name indicates, have ten feet or arms surrounding the 

 mouth, and in them the body is usually elongate, con- 

 taining a horny "pen" or calcareous "bone." This 

 group includes the cuttlefishes or sepias, from which are 

 obtained sepia ink and the cuttlefish bone used to feed 



