TEGUMENTARY ORGANS 425 



different states of contraction, relatively to one another, successive 

 changes in the colour of the spot. 



Among the Vertebrata the Chama^leon, as is well known, presents 

 similar phenomena. 



PapillcB of the enderon. — The enderon is frequently produced into 

 conical or cylindrical processes, which either merely contain a vascular 

 loop, or are supplied, in addition, with special nerves. In the Inverte- 

 brata, 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 processes in the 

 Ascidians, as vascular papillae. Among the Articulata like processes 

 extend, in the Crustacea, through the whole thickness of the integu- 

 ment 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 Lamelli- 

 branchs and Gasteropods, the papillae of Onchidium, &c. and those of 

 Tremoctopus (H. Muller) are very probably both vascular and 

 nervous papillae like those of fishes. 



Among the Vertebrata, fishes present large projecting papillae^ 

 particularly about the region of the lips and operculum, which are 

 both vascular 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 surface 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 exception to this rule ; it is stated (Heusinger, 

 Breschet, and Roussel de Vauzeme) that the very thick integument 

 of these animals is traversed by vascular and nervous papillae, four or 

 fives 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 papillae are, as is well 

 known, so abundant as to 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 Leydig for showing that in certain 

 Crustacea, Insecta, and Mollusca, it is very similar to what occurs in 



