64 MANUAL OF THE MOLLUSCA. 



The skin of the naked cephalopods is remarkable for its variously coloured 

 vesicles, or pigment-cells. In sepia 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 driven into the deeper 

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

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

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

 ing its hue, like the chameleon. In fresh specimens, the sclerotic plates of 

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



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

 the arms (drackial), or at their bases (buccal pores). 



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

 ("nuchal") muscular band; but its margin is sometimes free all round, and 

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

 and allowing considerable freedom of motion. 



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- 

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

 sea, hundreds of miles from land. They attain occasionally a much greater 

 size than any other mollusca. MM. Q,uoy and Gaimard found a dead cuttle- 

 fish in the Atlantic, under the equator, which must have weighed 2 cwt. when 

 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, which was estimated to have measured six feet in length. (Owen.) 

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

 it is difficult 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. Body 

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

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

 mental gland. Shell external and one-celled (mono-thalamous) > 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'Orbigny. 



t Denys Montfort, 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'Orbigny.) 



