64 MANUAL OF THE MOLLUSCA. ^ 



Tlie skin of tlie naked cephalopods is remarkable for its variously coloured ^ 



vesicles, or pigment-cells. In sep'uc they are black and brown ; in the calamary, : 



yellow, red, and brown ; and in the argonaut, and some octopods, there are ^^ 



blue cells besides. These cells alternately contract and expand, by which the | 



colouring matter is condensed or dispersed^ or perhaps di-iven into the deeper j 



part of the skin. The colour accumulates, like a blush, when the skin is ixjfL- \ 



tated, even several hours after separation from the body. During life, these j 



changes are under the control of the animal, and give it the power of chang- ; 



ing its hue, like the chameleon. In fi'esh specimens, the sclerotic plates of i 



the eyes have a pearly lustre ; they are sometimes preserved in a fossil state, j 



The aquiferous pores are situated on the back and sides of the head, on ' 



the arms {brachial), or at their bases {buccal pores). \ 



The mantle is usually connected with the back of the head by a broad 'i 



{"nuchaV) muscular band; but its mai'gin is sometimes free all round, and i 



it is supported only by cartilaginous ridges, fitting into corresponding grooves,* • 



and allowing considerable freedom of motion. i 



The cuttle-fishes are nocturnal, or crepuscular animals, concealing them- | 



selves during the day, or retiring to a lower region of the water. They in- i 



habit every zone, and are met with equally near the shore, and in the open t 

 sea, hundi-eds of miles fi-om land. They attain occasionally a much greater-^ 



size than any other moUusca. jMJNI. Quoy and Gaimard found a dead cuttle- j 



fish in the Atlantic, under the equator, which must have weighed 2 c\^'t. wheu i 



perfect ; it was floating on the surface, and was partly devoured by birds* ; 



Banks and Solander, also met with one under similar circumstances, in the « 



Pacific, wluch was estimated to have measm'ed six feet in length. {Owen.) \ 



The arms of the octopods are sometimes two feet long.f Trom their habits, j 



it is difiicult to capture some species alive, but they are frequently obtained, | 



uninjured, from the stomachs of dolphins, and other fishes which prey upon | 

 them. 



SECTION A. OcTOPODA. 



Arms 8 ; suckers sessile. Eyes fixed, incapable of rotation. Bodi/ 



united to the head by a broad cervical band. Braiichial chamber divided .] 



longitudinally by a muscular' partition. Oviduct double ; no distinct nida- ' 

 mental gland. Shell external and one-celled {mono-thalarnous), or internal 

 and rudimentary. 



The Octopods differ from the typical cuttle-fishes in having only eight- \ 

 arms, without the addition of tentacles ; their bodies are round, and they sel- 



* Termed the " apparatus of resistance," by D'Orbiguy. 



+ Benijs Monffort, having represented a " kraken octopod," in the act of scuttling 

 a three-master, told M. Defrance, that if this were " swallowed," he would in his next 

 edition represent the monster embracing the Straits of Gibraltar, or capsizing a whole • 

 squadron of ships. {D'Orbigmj.) 



