LEAVES FROM THE NOTE-BOOK OF A NATURALIST. 



113 



structure and properties of the colorific stratum 

 of the skin of the cephalopoda, upon which the 

 observations of M. Milne Edwards are in a great 

 measure based. Professor Owen quotes it in his 

 admirable article " Cephalopoda," in the Cyclo- 

 peedia of Anatomy and Physiology ; and, as this 

 part of the organization of those mollusks is the 

 key to the changes of color in the chameleon, 

 those who are interested in the subject may like 

 to see a brief account of the mechanism by which 

 the changes are effected in the marine animals. 



The epidermis of the cephalopods generally 

 forms a thick, white, semi-transparent, elastic, 

 external layer, which is easily detached by macer- 

 ation. Professor Owen remarks, that the color- 

 ific 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 that the 

 nature of this layer, when thoroughly understood, 

 may be expected to elucidate the mysterious opera- 

 tions of light in producing and affecting the colors 

 of animals. This stratum, which is analogous to 

 the rete mucosum which gives color, or " com- 

 plexion," as it is termed, to man, consists, he 

 observes, of a very lax and fine vascular and 

 nervous cellular tissue, containing an immense 

 number of small closed vesicles, which vary in 

 relative sizes in different species. These vesicles 

 are of a flattened oval or circular form, and con- 

 tain a fluid in which a denser coloring matter is 

 suspended. The color is not always identical in 

 all the vesicles, but, in general, corresponds more 

 or less closely with the tint of the secretion of the 

 ink-bag with which this race is furnished as a 

 protection ; for, as is known to all who have 

 observed their habits, their first act when surprised 

 is to eject this inky fluid, succus nigrce. loliginis, 

 that they may escape under cloud of the discolored 

 water. In the common cuttle, Sepia, besides the 

 vesicles which correspond to the ink in the color 

 of their contents, there is another series of an 

 ochre color. In the common pen-and-ink fish, 

 Loligo vulgaris, there are three sorts of colored 

 vesicles, yellow, rose-red, and brown. In Loligo 

 sagitlata there are four kinds saffron, red, black- 

 ish, and bluish. The paper Nautilus, Argonauta 

 Argo, possesses vesicles of all colors, which have 

 been observed in other cephalopods, and hence the 

 variety and change of color which its skin presents 

 when exposed to the light. The rest of this in- 

 teresting organization will be best conveyed in the 

 professor's own words : 



These vesicles have no visible communication 

 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 of repose, and the vesicles 

 are contracted and invisible, the skin be slightly 

 touched, the colored vesicles show themselves, and 

 in an instant, or sometimes with a more gradual 

 motion, the color will be accumulated like a cloud 

 or a blush upon the irritated surface. If a portion 

 of the skin be removed from the body and immersed 



in sea-water, the lively contractions of the vesicles 

 continue ; when viewed in this state under the 

 microscope by means of transmitted light, the edges 

 of the vesicles are seen well defined, and to pass in 

 their dilatations and contractions over or under 

 one another. If the separated portion of integu- 

 ment be placed in the dark, and examined after a 

 lapse of ten or fifteen minutes, all motion has 

 ceased ; but the vesicles, when reexposed to a 

 moderately strong light, soon, in obedience to that 

 stimulus, recommence their motions. As the vibra- 

 tile microscopic cilia have been recently traced 

 through the higher classes of the animal kingdom, 

 it is not an unreasonable conjecture that equally 

 inexplicable motions of the coloring parts of the 

 integument may also be detected in other classes 

 than that in which we have just described them, 

 and thus a clue may be obtained towards the expla- 

 nation of the influence of geographical position OB 

 the prevailing colors of the animal kingdom. 



This is a most seducing and interesting subject, 

 well worthy of consideration and further experi- 

 ment ; but at present we must return to our 

 chameleons. Just see how admirably the adapta- 

 tion is carried on throughout. The free foot, 

 formed in some of the other lacertians for running 

 nimbly over the sand or through the herbage, with 

 the aid of the disposition of the other limb bones, 

 is here changed into an organ essentially prehensile. 

 The two wrist-bones, which are next to those of the 

 forearm, are articulated upon one central piece, 

 which receives the five bones that correspond to th 

 metacarpal. Three of these are for the anterior toes, 

 and two for the posterior ; and the whole five finger 

 bones are bundled up in the integuments to the claws, 

 three in the fore bundle and two in the hind bundle, 

 forming a most efficient clinging instrument when 

 applied to the branch of a tree. The toes of the 

 hinder extremities are disposed in the same oppos- 

 able manner. The creature in its natural state, 

 planted firmly among the foliage, and holding 

 tenaciously on by its feet and tail, varying its 

 color at pleasure in the chequered light and shade, 

 looks more like an excrescence of the tree than an 

 animated being ;* and woe to the luckless insect 

 that, deceived by appearances, ventures within 

 reach of its unerring tongue ! For, though the 

 shortness of its neck and its enormous occiput for- 

 bid it to turn its head, which it can no more do 

 than a carp or a codfish, the sweep of its vision is 

 very great. Take up a chameleon's skull, and 

 observe how large a space is occupied by the 

 orbits. In these capacious receptacles ample room 

 is afforded for the large globe and the muscles 

 which are to direct it. The pupil looks like an ani- 

 mated gem set in shagreen, and this versatile globe 

 is capable of the most varied and extensive direo- 

 tion. This, as worthy Dr. Goddard says, " she 

 turneth backward or any way, without moving her 



* The Tarandus of Pliny will occur to those of our 

 readers who are conversant with his wonderful maga- 

 zine, where the beast is described as being as big as 

 an ox, and when he pleaseth, assuming the color of an 

 ass. But this is a small sample of his versatility, for 

 "he reflects the colors of all shrubs, trees, flowers, 

 and of the place where he lies, and hiding himself 

 from fear, he is on that account very rarely taken." 

 Nat. Hist. viii. 34. 



