CEPHALOPODA. 



543 



In the Nautilus (Jig- 224) there is a larger and 

 smaller branchia on each side; the larger and 

 external branchia (m) presents forty-eight pairs 

 of laminae; the smaller branchia (n) thirty-six. 



In the Dibranchiates the gills vary in the 

 relative size and number of laminae in different 

 genera; they are, perhaps, proportionally small- 

 est in the Loligopsis, where, according to 

 Rathke, the number of branchial laminae does 

 not exceed twenty-four pairs ; and it is inte- 

 resting to observe in this genus that the mus- 

 cular structure of the mantle has a correspond- 

 ingly feeble development. In the Cuttle-fish 

 the branchiae are each composed of thirty-six 

 pairs of triangular laminae : in the Sagittated 

 Calamary of sixty pairs of laminae. 



As the branchiae of the Cephalopods are un- 

 provided with vibratile cilia, respiration is 

 effected by the alternate dilatation and contrac- 

 tion of the branchial chamber ; in the first ac- 

 tion the sea-water rushes in by the anterior aper- 

 ture of the mantle ; by the second it is expelled 

 through the cavity of the funnel. As in other 

 classes, respiration is performed more quickly 

 in the young than in the full-grown animals : 

 Dr. Coldstream witnessed an Eledone, which 

 measured one inch and a half in length, respire 

 eighteen times in a minute; while one of the 

 same species, which measured four inches in 

 length, respired ten times in a minute. The 

 proper direction of the respiratory currents is 

 insured by various mechanical contrivances ; in 

 the Nautilus, the funnel passes through a hole in 

 the substance of the mantle, which fits it so 

 closely, that at the moment when the funnel is 

 distended by the expiratory stream, no space is 

 left external to it by which the water can 

 escape ; and the greater the force by which the 

 water is driven into the funnel, the closer is it 

 girt by the mantle. In the Poulp and Eledone, 

 where the funnel is connected to the fore part 

 of the neck, and the mantle passes across its 

 base, two large valvular folds (one of which is 

 shown at v,Jig. 216) are extended from its sides; 

 these are concave towards the respiratory sac; 

 they subside during inspiration, and the parietes 

 of the funnel at the same time are collapsed ; 

 the latter during expiration are dilated, while 

 the valves are raised and expanded, and thereby 

 prevent the ejected currents from passing out- 

 side the funnel. In the Argonaut, and in 

 all the Decapods, except the Loligopsis and 

 Cranchia, the sides of the funnel are articula- 

 ted to the opposite sides of the mantle by ball- 

 and-socket joints, which produce so close an 

 apposition of the anterior free margin of the 

 mantle with the parts it surrounds, that upon 

 its contraction, no other outlet, save the funnel, 

 is left for the expiratory currents. In the Ar- 

 gonaut the pallial eminence is a round tuber- 

 cle, below which is a small cavity, and these 

 are adapted to a cavity and tubercle of corre- 

 sponding form at the side of the funnel. In 

 Sepia, the articular tubercle is elongated in the 

 direction of the axis of the body, and is of an 

 oval form. In Loligo and Onychoteuthis it is 

 still more elongated and narrow, and the arti- 

 cular depression is conformable : in Loligopsis 

 the corresponding cartilage is no longer sub- 



servient to an articulation with the funnel, but 

 is represented by a series of wart-like knobs. 



TEGUMENTARY SYSTEM. The skin of the 

 Cephalopods is thin and lubricous, and can 

 be more easily detached from the subjacent 

 muscles than in the inferior Molluscous classes. 

 In the Poulp, Eledone, Argonaut, Cuttle-fish, 

 and Sepiola, its texture is soft and tender, and 

 the whole mantle is semitransparent in some 

 species, as the Octopus hyalinus ; but in the 

 Calamaries and Onychoteuthides it is thicker, 

 harder, and more unyielding ; it is interesting 

 to observe that it is in these latter genera that 

 the epidermoid system is most developed, as. 

 is exemplified in the horny denticulations and 

 hooks upon the acetabula. 



In the Cuttle-fish the suckers are provided 

 with simple unarmed horny rings. In the 

 Octopods the epidermis is reflected over the 

 interior of the suckers without being thickened 

 into a horny substance at that part. In the 

 body generally the epidermis is readily de- 

 tached by maceration, and forms a thick, white, 

 elastic, semitransparent, external layer. 



The colorific stratum of the integument forms, 

 both in its structure and vital phenomena, one 

 of the most curious and interesting parts of the 

 organization of this singular class of animals ; 

 and the nature of which, when thoroughly un- 

 derstood, may be expected to elucidate the 

 mysterious operations of light in producing 

 and affecting the colours of animals. 



This stratum, which is analogous to the 

 rete mucosum, consists of a very lax and 

 fine vascular and nervous cellular tissue, con- 

 taining an immense number of small closed 

 vesicles, which vary in relative sizes in different 

 species of Dibranchiata. These vesicles are of 

 a flattened oval or circular form, and contain a 

 fluid in which is suspended a denser colouring 

 matter. The colour is not always the same in 

 all the vesicles, but in general corresponds 

 more or less closely with the tint of the secre- 

 tion of the ink-bag. This, for example, is the 

 case in Sepiola, in which all the vesicles con- 

 tain material of the same colour. In Sepia, be- 

 sides the vesicles which correspond to the ink 

 in the colour of their contents, there is another 

 series of an ochre colour. In Loligo vulgaris 

 there are three kinds of coloured vesicles, yel- 

 low, rose-red, and brown. In Loligo sagittata 

 there are four kinds, saffron, rose-red, deep 

 blue, and light blue. In Octopus vulgaris there 

 are also four orders of vesicles, viz. saffron, red, 

 blackish, and blueish. The Argonauta Argo 

 possesses vesicles of all the colours which have 

 been observed in other Cephalopods, and hence 

 the variety and change of colour which the 

 surface of its skin presents when exposed to 

 the light. 



These vesicles have no visible communica- 

 tion either with the vascular or the nervous 

 systems, or with each other : yet they exhibit, 

 during the life-time of the animal, and long 

 after death, rapid alternating contractions and 

 expansions.* If, when the animal is in a state 



* Conf. Dr. Coldstream in Edinb. Journal of 

 Natural and Geographical Science, vol. ii. p. 297. 



