272 



THE CEPHALOPODA. 



§234. 



delicate elastic membrane ; when contracted, their form is round, but it 

 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 form 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-membraae, but to the con- 

 tractile fibres of the dermis which are united in 

 them, and whicli, upon contraction, pull at their 

 point of insL'rtion, tlius 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 Kolliker, Ent- 

 wick. d. Cephalopoden, p. 71, and Harless, loc. cit.). 

 When these cells are dilated, the pigment granules 

 are often removed from the centre to the periphery 

 of the cell, thus forming a central, coloi'less trans- 

 parent spilt, which has been regarded by Wagner 

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



3 These so highly characteristic chromatic cells 

 of the Cephalopoda, are found also in the slcin of 

 Hectocotylus, and are, therefore, one of the data 

 for determining the nature of these animals, which 

 have hitherto been regarded as trematode parasites. 

 Delle Chiaje and Costa (loc. cit.) have repre- 

 sented these cells in a colored figure of Hecto- 

 cotylus ari^onautae. I have, also, distinctly seen 

 them with individuals of Hectocolylus tremoc- 

 topodis preserved in alcohol. 



As Grube (Akthiien, Echinodermen und Wiir- 

 mer des Adriat. und Mittel-Jleeres, p. 49, fig. 2) 

 has observed these same chromatic cells in the skin 



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

 porus r.hrimneleon, it is certain that this animal, 

 found on the branchiae of a marine fish, is only a 

 torn off arm of one of the Loligina. The presence 

 of these cells in the skin of Ifautilns seems proved, 

 for Ruinph (Amboiuische Raritiiten-Kammer von 

 Schnecken und Muscheln, 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 ilollusk, which (^uoy and 

 Gaimard found at the Celebes islands, and which 

 they thought to belong to Nautibis pompiliux 

 (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 Cephalnpod, it should have the 

 chromatic cells, a point which may yet, ])erhap3, be 

 determined from the preserved si)ecimen 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 pompilius, 

 abortive as to its form and size .' 



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

 chromatophoric contractile sacs. The splendid 

 changeable colors of the surface appeared to be 

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

 tervening tissue ; and the surface color over the 

 pigment spots is subject to thj 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 aiipearances of these animals ap- 

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

 face phenomena as to pigment , and I haye failed 

 to detect different layers of pigment as described by 

 Owen ; see Burnett, Proceed. Host. Soo. Nat. Hist. 

 IV. p. 252. — Ed. 



