272 



THE CEPHALOPODA. 



^ 234. 



delicate elastic membrane ; when contracted, tlieir form is round, but iti 

 becomes dentate on dilatation. The pigment granules, which they enclose, 

 are always of the same color in each cell, and produce the red, the yellow- 

 ish-brown, the blue, or violet spots, whose extent and shade vary, accord- 

 ing as the cells are contracted or dilated.'-^ Usually, adjacent cells have- 

 very different colors, and to their alternate contractions and dilatations in 

 groups, are due those magnificent chromatic changes which have long made 

 celebrated the skin of the Cephalopoda/'^' 



These contractions, and consequently these chromatic changes, are under 

 the influence of the nervous system. This is the reason of their decrease 

 or disappearance, or their reappearance and increased brilliancy, in certain 

 places, when the neighboring or even the distant skin is irritated. More- 

 over, the fibres of the corium preserve their contractility after having been 

 detached, so that the chromatic changes may be observed on portions of 

 the skin that have been removed. 



§ 234. 



Behind the neck of the Cephalopoda, the skin forms a large sac-like 

 mantle, which completely envelopes the trunk, but is adherent only upon 

 the back. Its anterior border is free, and can embrace, like a sphincter, the 

 neck and posterior part of the head. Under the throat, the skin is pro- 

 longed in the foi^ of a funnel, the free apex of which extends in front, 

 while the broad base communicates with the cavity of the mantle, and is 



2 The movements of the chromatic cells are not 

 directly due to the cell-membrane, but to the con- 

 tractile fibres of the dermis which are united iu 

 them, and which, upon contraction, pull at their 

 point of insertion, thus producing the ragged as- 

 pect of these cells when expanded. They return to 

 their round form when the fibres are relaxed, from 

 the elasticity of the cell-walls (see KöUi/cer, Ent- 

 wick. d. Cephalopjden, p. 71, and Hartess, loc. cit.). 

 "When these cells are dilated, the pigment granules 

 are often removed from the centre to the perijihery 

 of the cell, thus forming a central, colorless trans- 

 parent spot, which has been regarded by fVagner 

 (loc. cit.) as the nucleus of the cell. 



3 These so highly characteristic chromatic cells 

 of the Cephalopoda, are found also in the skin of 

 HectocotylLiS, and are, therefore, one of the data 

 for determining the nature of these animals, which 

 have hitherto been regarded as trematode parasites. 

 Delle Cliiaje and Costa (loc. cit.) have i-epre- 

 Bented these cells in a colored figure of Hecto- 

 cotylus nrfronautae. I have, also, distinctly seen 

 them with indiviiluals of Hectocotylus tremoc- 

 topodis preserved in alcohol. 



As Grube (Aktinien, Echinodermen und Wür- 

 mer des Adi-iat. und Mittel-.Meeres, p. 49, fig. 2) 

 has observed thuse same chromatic cells in the skin 



of a genus of parasites, which he has called Poly- 

 porus chamaeleon, it is certain that this animal, 

 found on tlie branchiae of a marine fish, is only a. 

 torn off arm of one of the Loligina. The presence 

 of these cells in tlie skin of Nautilua seems proved, 

 for Rumph (.\mboinische Raritäten-Kammer von 

 Sclinecken und Musclieln, p. 7) expressly declares 

 of this animal which he saw living, that " its upper 

 portion is reddish or bright brown with some black 

 spots, which as with the cuttle-fish, become faded." 



The fragment of the Mollusk, which Quoy and 

 Gaimnrd found at the Celebes islands, and which 

 they thought to belong to Nautilus pu7npilius 

 (Ann. d. Sc. Nat. XX. 1830, p. 470, PI. XIV. 

 A. or Isis, 1834, p. 1146, Taf. XV. A. B.) 

 deserves our attention in various ways. If it 

 really belonged to a Cephalopod, it should have the 

 chromatic cells, a point which may yet, perhaps, be 

 determined from the preserved specimen at Paris. 



In the colored figure which these naturalists have 

 given of it, the skin is dotted with red, — a presump- 

 tion in favor of the existence of these cells. 



But, indeed, is it not possible that this animal, 

 from its resemblance to the Hectocotyli, is not a 

 mutilated one, but the male of Nautilus pompiliuSf 

 abortive as to its form and size i 



ment, deposited, as he has so well described, in the 

 chromatoph>jric contractile sacs. The splendid 

 changeal)le colors of the surface appeared to be 

 due, not to the pigment spots alone, but to the in- 

 tervening tissue ; ami the surface color over the 

 pigment spots is subject to the same variations. 

 Thus, a bistre-brown spot will sometimes appear 

 blue, then green, &c. These facts may be tested 

 by placing a small portion of the skin on a plate of 



glass, and introducing a little water under it, the 

 evaporation of which,- by changing the surface con- 

 ditions, generally produces a variety of colors. 



The chromatic ai)pearance3 of these animals ap- 

 peared to me, therefore, as due full as much to sur- 

 face phenomena as to pigment , and I have failed 

 to detect different layers of pigment as described by 

 Owen ; see Burnett I'rocecd. Bost. Soo. Nat. Hist, 

 IV. p. 252. — Ed. 



