1898.] BREEDING OF THE DBAGOTSTET. 297 



Though difiFerentiated males exhibit their dorsals, and especially 

 the second, much more readily than other members of their species, 

 they by no means neglect an opportunity to escape observation. 

 Thus I have several times seen a male, approached by a dangerous 

 intruder, remain quite still except for the movements of the eyes. 

 If the enemy showed signs of approaching too near, the Dragonet 

 would stir shghtly and even commence to raise its fins, but these 

 were at once dropped again when it appeared that the enemy 

 was about to pass on. This happened after the breeding-season, 

 when the male Dragonets were by no means conspicuous when at 

 rest. 



V. Preliminary Discussion of the Colour-Mechanism and 

 Differentiation of Coloration. 



It is known that in birds the sexual differences of coloration, 

 though often very striking, are not due to the presence in one sex 

 of any pigment that is not present in the other. The diverse 

 effects result from differences in the texture of the feathers, 

 involving diverse conditions of interruption of the pigment 

 (cf. Beddard, ' Animal Coloration,' p. 4 ). As might be supposed, 

 the same pigments are present in both sexes of Callionymus. They 

 consist of a yellow, probably a lipochrome, and a black, which 

 may be presumed to be melanin. The researches of various 

 observers have shown that the elements which contribute to the 

 coloration of the Teleostean skin are (i.) pigments, whether 

 contained in chromatophores or partially diffused, (ii.) a reflecting 

 substance, distributed in a variable manner and found to consist, 

 in cases that have been investigated, either of guanin or " guanin- 

 kalk," a combination of the former with lime. Isolated cr^^stals 

 of calcium phosphate have been detected in some forms, while 

 haemoglobin in the underlying muscles is an occasional contributor 

 to the superficial coloration. It will be readily understood that 

 variation in the distribittion of yellow and black pigments alone 

 may produce in different parts of the skin a range of coloration 

 from pure yellow through brown to black, while manipulation by 

 expansion or contraction of individual chromatophores may give 

 rise to the well-known " protective " changes common to most of 

 the bottom-living fishes ^ Such changes occur in the female and 

 young male of Callionymus and in the parts of the adult male 

 which are not affected by the sexual differentiation, but need not 

 concern us here. Both the pigments and the reflecting substances 

 present in many fishes have received a certain amount of attention 

 by various authors. The reflecting substance in Alburnus and 

 Argentina has been shown to consist of guanin ^. The brilliance 

 of the iris in certain forms has been traced to the optical properties 



1 Cf. Agassiz, " Development of the Flounders," Proc. Amer. Acad. xiv. 1878, 

 p. 14, pi. viii. ; Cunningham, 'The Common Sole,' 1890, p. 110, pis. i.-iii. 



^ Barreswil, Compt. Eend. liii. 1861, p. 246. Voit, Zeitschr. wiss. Zool. xv. 

 1865. 



