FISHES 



best be regarded as the involuntary result of excitement. 

 The elongated fins may alarm small and timid specimens of 

 the same species, merely as any sudden movement will 

 alarm and frighten them away, but it is obvious that these 

 fins are not in themselves formidable. All dragonets possess 

 weapons of some importance in the three-spined projection 

 on their opercula, which can be thrust out from the sides of 

 the head at will. These seem to be used for defence, and 

 are not specially associated with the peculiarities of the adult 

 male. 



We have now to bestow some consideration on the 

 peculiarities of coloration in the mature male. In the case 

 of the dragonet, as in most, if not all other cases, the differ- 

 ence in the colour of male and female is a quantitative, not a 

 qualitative difference. That is to say, the same pigments 

 are present in both sexes, but in different amounts. These 

 pigments are a yellow, probably of the kind known to 

 physiological chemists as lipochromes, and a black, known as 

 melanin. The colour of this and other fishes does not, how- 

 ever, depend on pigments alone, but partly on a reflecting 

 substance disposed in various ways, and found to consist 

 chemically of a substance called, from its presence in guano, 

 guanin. The pigments are largely contained in definite 

 bodies known as chromatophores, which consist of branch- 

 ing processes radiating from a common central disc. The 

 chromatophores are of microscopic size, and under nervous 

 influence in the living fish are capable of extending or con- 

 tracting their processes, changes which have a marked effect 

 on the temporary coloration. 



The young male and female are identical in coloration, so 

 that the peculiarities of the adult male are due to changes 

 that take place in the coloration elements of the young 

 male. In the latter the second dorsal fin is marked by 

 horizontal broivn bands, alternating with bands of opaque 



14 



