30 THE WONDER OF LIFE 



spinal nerves to the skin, and finally the state of con- 

 traction of the pigment cells just below the surface. Any 

 one may see a lemon-sole, for instance, putting on its gar- 

 ment of invisibihty. Until one catches sight of its eyes, 

 it seems to be completely lost in its background. The 

 invisibility is sometimes further ensured by a dusting of 

 sand, but it is remarkably complete without that. 



It may be explained that the outer skin or epidermis 

 of fishes is dehcate and transparent. All the colour is in 

 the dermis, and it usually occurs in remarkable pigment- 

 cells or chromatophores. These typically show numerous 

 radiating processes, and the pigment can be spread out 

 to the periphery or concentrated in the centre, according 

 to the expansion or contraction of the mobile protoplasm 

 of the pigment-cell. According to the pigment which 

 they contain — black, yellow, red, and so on — the pigment- 

 cells are called melanophores, xanthophores, erythrophores, 

 and so forth. Then there are other cells containing spangles 

 of the waste- product guanin, which are called iridocyi;es or 

 guanophores. They cause the silvery, metallic, or iridescent 

 appearance famihar on many fishes. Professor Ballowitz 

 has recently discovered, in the Weaver and some other 

 Bony Fishes, a new kind of chromatophore, consisting of a 

 group of cells — a cluster of iridocytes with an encapsuled 

 central melanophore which sends its ramif3dng process 

 through the capsule in comphcated courses. 



The story goes that a chameleon, whose power of 

 colour-change is famous, reached the hmit of its capacity for 

 ' sympathetic coloration ' when it was placed in a tartan- 

 lined box. It soon died, with a pained expression of baffled 

 adaptabihty, but some of the achievements of flat-fishes 

 in the way of harmonizing with their surroundings do not 



