CEPHALOPODA. 343 



removed from the body and placed in sea-water under the microscope, 

 the contractions of the vesicle may be watched for some time : their 

 margins are well defined, and they pass, during their dilatations or 

 contractions, over or under one another. The power which the 

 Cephalopods possess of changing their colour and of harmonizing it 

 with that of the surface on which they rest, is at least as striking and 

 extensive as in the Chameleon, in which, it seems, from the latest 

 observations, to be produced by a similar property and arrangement 

 of pigmental cells. 



The internal organised skeleton of the dibranchiate Cephalopod 

 is cartilaginous, as in the Nautilus, but consists of a greater number 

 of pieces, and enters into a larger proportion of the organisation of 

 the animal. The cranial cartilage is no longer limited in its position 

 to the under side of the oesophagus, but completely surrounds that 

 tube, which, together with the inferior salivary ducts and the cephalic 

 branches of the aorta, traverses a narrow canal in its centre. The 

 cartilage expands above into the cavity containing the brain, while 

 below it is excavated to form the organ of hearing, and at the sides 

 expands into the broad and thick orbital cavities. There is also a 

 thin and long cartilage which supports the eyeball^ and seems to be 

 analogous to the ophthalmic peduncle of the Rays and Sharks. A 

 process continued from the anterior part of the cranial cartilage ex- 

 pands into a broad transverse plate^ and gives attachment to the 

 muscles of the arms. The infundibular cartilage, which is a process 

 of the cranial one in the Nautilus^ is a distinct piece in the Dibran- 

 chiata. It is of a large size, and of a flattened triangular figure in 

 the cuttle-fish, in which it is situated above the base of the funnel. 

 It consists of three distinct portions in the Calamary. On each side 

 the base of the funnel there is a smooth oblong articular cavity, formed 

 by a distinct piece of cartilage, which is articulated with a corre- 

 sponding cartilaginous prominence from the inner surface of the side 

 of the mantle. These cartilaginous joints of the funnel vary in shape 

 in the diff'erent genera : they are wanting in the Octopus. The 

 lateral fins of the Decapoda are each supported by a narrow flattened 

 elongated cartilaginous plate, which forms the medium of attachment 

 of the powerful muscles of those fins. These appear to be analogous 

 to the pectoral fins of fishes ; but as they are not fixed to a vertebral 

 column, their position is variable ; in the Rossia^ for example, they are 

 situated near the anterior part of the body ; in the Loligo^ they are 

 placed at the posterior extremity : in the Sepia they extend, like the 

 great pectoral fins of the Rays, along the whole side of the body. In 

 the Octopods the mantle-fins and their cartilages are wanting, except 



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