X THE COLOURS OF FISHES 223 



not be in addition some assisting optical effect. 

 A similar but even more interesting case is that 

 of the green pipe-fish {Siphonostoma typMe), often 

 quoted as an instance of protective resemblance. 

 In this form a similar combination of yellow and 

 black pigment occurs, but there is some doubt 

 whether the green colour is not in part due to the 

 action of the reflecting tissue. This pipe - fish, 

 though usually green, may appear in a brown form, 

 while the common pipe - fish (Syngnathus acus) is 

 always brown. The common pipe-fish also contains 

 yellow and black pigments, but the yellow is said by 

 the authors to be more orange-coloured than that 

 of the preceding form. It is, however, curious to 

 note that the three pigments, that of the mackerel 

 (^Scomber scomber) and those of the two pipe-fishes, 

 yield solutions whose spectroscopic characters are 

 almost the same ; this certainly suggests that the green 

 is primarily a result rather of structure than of pig- 

 ment. True green pigments in fishes were, however, 

 described some time ago by Mr. G. Francis in certain 

 of the Wrasses (species of Odax and Labrichthys), 

 but the observations have never been repeated. 

 The Mediterranean members of the family are said 

 by Krukenberg to owe their green and blue colours 

 to structural effects. 



In general, we may say of the colours of fishes 

 that they are either pigmental or structural, and that 

 the only pigments which have been described with 

 certainty are lipochromes or melanins. In most 

 cases both kinds of pigments occur simultaneously, 

 but in some, as in the gold-fish {Carassius auratus), 

 the melanin pigments are entirely absent. The 



