TEGUMENTARY ORGANS. 



503 



and of irregular more or less stellate masses 

 which are not enclosed in cells. The silvery 

 lustre of the skin of fishes is due to minute 

 rods which constitute a layer at this surface, 

 and should probably be regarded as a peculiar 

 form of pigment granules. 



In the Cephalopoda and some Gasteropoda 

 among the Invertebrata, the integument 

 undergoes during life the most extraordinary 

 variations of colour, becoming overspread 

 with successive clouds of the most vivid hues. 

 These are produced by the contraction and 

 expansion of peculiar sacs the chromato- 

 phora containing masses of pigment granules. 

 According to 11. Miiller, (whose observations 

 I have recently had the opportunity of re- 

 peating,) these are sacs attached to whose 

 walls are contractile fibre cells arranged ra- 

 dially, and frequently anastomosing with those 

 of other cells. They do not always contain 

 pigment, but frequently present a distinct nu- 

 cleus. Several layers of these chromatophora 

 of different colours are frequently disposed, 

 one over the other, in a given portion of the 

 skin, and produce by their different states of 

 contraction, relatively to one another, suc- 

 cessive changes in the colour of the spot. 



Among the Vertebrata the Chamseleon, as 

 is well known, presents similar phenomena. 



PapUlcB of the enderon. The enderon is 

 frequently produced into conical or cylin- 

 drical processes, which either merely contain 

 a vascular loop, or are supplied, in addition, 

 with special nerves. In the Invertebrata, we 

 find, in the processes of the mantle into the 

 shell of the Brachiopoda described by Dr. 

 Carpenter, organs which, I have no doubt, 

 must be regarded, like the corresponding pro- 

 cesses in the Ascidians, as vascular papillae. 

 Among the Articulata like processes extend, in 

 the Crustacea, through the whole thickness of 

 the integument to its surface, giving rise to the 

 colourless spots observable on the shell of the 

 crab, for instance. I imagine, however, that 

 these spots were usually occupied by a hair 

 when the shell was thin. In the Mollusca, 

 the marginal processes of the mantle of the 

 Lamellibranchs and Gasteropods, the papilla? 

 of Onchidium, &c. and those of Tremoctopus 

 (H. Miiller) are very probably both vascular 

 and nervous papilla? like those of fishes. 



Among the Vertebrata, fishes present large 

 projecting papillae, particularly about the region 

 of the lips and operculum, which are both vas- 

 cular and nervous. Simple papillae (nervous ?) 

 are scattered over the surface of the body in 

 Plagiostomes and some Ganoid fishes. 



I am not aware that papillae have hitherto 

 been observed on the integument of Birds 

 and Reptiles. In most Mammals, they are very 

 small, if they exist at all, upon the general sur- 

 face of the body, attaining a considerable size 

 only in such organs as the ball of the foot 

 (Cat, Dog), or on the muzzle. The Cetacea, 

 however, appear to make a remarkable excep- 

 tion to this rule ; it is stated (Heusinger, 

 Breschet, and Roussel de Vauzeme) that the 

 very thick integument of these animals is tra- 



versed by vascular ami nervous papilla', four 

 or five lines long, which extend as far as the 

 outer horizontal horny layer of the ecderon, 

 so that a horizontal section of the ecderon is 

 like that of a horse's hoof. In man, again, the 

 papilla? are, as is well known, so abundantasto 

 have given rise to the term pars-papillaris, for 

 the superficial layer of the ecderon. The 

 structure of those which appear to possess 

 special nervous functions will be considered 

 below. 



Sensory appendages of the enderon. Very 

 little is known of the ultimate distribution of 

 the nerves to the integument in the Inverte- 

 brata, but we are indebted to Levdig for 

 showing that in certain Crustacea, Insecta, and 

 Mollusca, it is very similar to what occurs in 

 the vertebrate classes. Thus in Argulus 

 follaceus the peripheral nerves become pale, and 

 divide, and at the point of division there is a 

 ' nucleus ' as in the embryonic fibres of the 

 frog. In Artemia salina, Branchipus st agnails, 

 and in the Heteropod Mollusk Carinaria, the 

 termination of the tegumentary nerves is es- 

 sentially similar. The larva of the Dipterous 

 insect Corethra, presents even peculiar sensory 

 appendages, in the delicate plumed hairs 

 which beset the sides of the body. These 

 are articulated in the ordinary way, and have 

 an internal ligament, a sort of spring, attached 

 to their base, which is enlarged and receives 

 the enlarged and cellaeform termination of a 

 nervous twig. It will be obvious that this 

 arrangement is peculiarly fitted for commu- 

 nicating the slightest vibration to the nerves. 



In the Vertebrata (fishes, reptiles, man), 

 the ordinary mode of termination of the 

 integumentary nerves is in one or two 

 plexuses, whence the fine terminal branches 

 proceed, and end by dividing into minute 

 branches indistinguishable from the imperfect 

 elastic fibrils of the enderonic tissue. Loops 

 have also been observed, but it is impossible 

 to say whether, in any case, these are real ter- 

 minations or not. Gerber and Kolliker have 

 also described " nerve coils" in animals, and 

 in the conjunctiva and lips of man. 



The simplest form of sensory appendage 

 in the Vertebrata is presented by the large 

 papillae of fishes, into which a bundle of nerve 

 fibres enters, some of which terminate in the 

 papillae, while others, whose looped bands may 

 be readily distinguished, probably pass out 

 again. 



In certain fresh-water fishes (Barbus, Leu- 

 ciscus), Leydig has described papillae of this 

 kind, which have a cup-shaped depression at 

 their extremities, lodging a globular mass of 

 what he describes as modified epithelium. 



Special modifications of the tissue of the 

 papillae for sensory purposes in the: fingers, 

 tongue, lips, &c. of man have lately been dis- 

 covered by Meissner and Wagner, and de- 

 scribed by them, under the denomination of the 

 Corpusculn tactus. Kolliker, who doubts their 

 special relation to the tactile function, on the 

 other hand, prefers to call these bodies, ii.cilc 

 corpuscles. They are simply ovoid masses of ini- 



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