214 SEXUAL DIMORPHISM 



pigment was not given off from the skin perceptibly during 

 life, but very soon after death it could be dissolved out readily 

 in fresh water and in sea-water, as well as in alcohol and 

 various other reagents commonly used for preserving speci- 

 mens. The colour of the solution was destroyed by acids, and 

 bleached very rapidly in light. He considers that its diminu- 

 tion in the living fish after the breeding season is more prob- 

 ably due to its diffusion into the water than to its bleaching 

 in situ, though no evidence of its presence in the water was 

 obtained. Indications of the degeneration of black chroma- 

 tophores causing the fading of the blue colour after the 

 breeding season were mentioned above. Whatever becomes 

 of the pigments and guanin in the skins of fishes, whether 

 they are excreted or reabsorbed, we have reason to believe 

 that they are not entirely permanent. Eeabsorption by the 

 blood probably enough takes place. If they are not perma- 

 nent a diminution of secretory activity in their production 

 would naturally lead to a diminution in the quantities present 

 in the skin, and thus we can understand why the brilliant 

 coloration of the male dragonet fades after his sexual excite- 

 ment has ceased for the season. It is scarcely necessary to 

 point out that this suggestion applies to numerous other 

 analogous cases. 



Before quitting the subject it may be mentioned that Mr. 

 Holt found the solution of the yellow pigment to have an 

 odour resembling that of an acrid cucumber, and a subacid 

 taste not particularly disagreeable, but causing a prolonged 

 irritation of the human salivary glands. He found that the 

 pigment was distasteful to several fishes, but neither distaste- 

 ful nor terrifying to young dragonets. It was unpalatable to 

 at least one predaceous fish, the pollack, but even fully- 

 coloured male dragonets were greedily eaten by the turbot. 



In most of the species of Gobius the male takes care of 

 the eggs. Gobius minutus scoops out the sand from beneath 



