304 ME. E. W. L. HOLT ON THE [Apr. 19, 



gated the colour-elements of the Teleostean skin suggest that 

 guanin is probably the most important component of the reflecting 

 tissue in CalJionymus. My friend Mr. G. Brebner has detected 

 its presence, and tells me that calcium is abundantly present 

 in all parts examined, including the loose inner layer containing 

 the argenteum. This was also the case in the reptiles, &c., 

 examined by Ewald and Krukenberg '. I have not found in 

 C'aUioni/mua any large crystals of calcium phosphate, such as 

 occur in the skins of some fishes. Judging from its optical effect, 

 I do' not suppose that the reflecting substance differs in chemical 

 composition in different parts of the skin or in individuals of 

 different ages. Apart from the yellow pigment I provisionally 

 suggest that the colour-change is caused (i.) by the excessive 

 development in the adult male of a reflecting substance (probably 

 guanin) common to both sexes and all stages, and by the 

 definite disposition of its particles in composite structures — the 

 prismatic bodies ; (ii.) by the distribution of black chromatophores 

 in relation to the said prismatic bodies. 



Agassiz and Ewald and Krukenberg refer to a paper by Briicke 

 (Sitz. Wien. Akad., math.-nat. Classe, Jahrg. 1851), which I have 

 not been able to consult. It appears that the author has dealt 

 with the mechanism of the well-known colour-changes in the 

 Chameleon, and demonstrated the property of cerulescence under 

 certaiii conditions of the reflecting elements, which Ewald and 

 Krukenberg subsequently found to be composed of guanin. We 

 have seen that in C'aUiony,m(s the property of cerulescence is 

 confined to the prismatic bodies (if ^e except the occasional 

 manifestation of the same property by particles of the masses of 

 reflecting tissue which underlie black cliromatophores), and that 

 these bodies are found in association with black pigment only. 

 With a view of testing the effect of the yellow pigment, I have 

 isolated pieces of the blue skin from one side of the dorsal fin and 

 compared the colour-effect of the prismatic bodies (i.) when the 

 skin is viewed alone, in its natural association with only black 

 chromatophores, (ii.) when the same skin is stretched over a bit of 

 the yellow part of the same fin. It is at once apparent that the 

 underlying yellow pigment changes the effect of the bodies as 

 seen by reflected light. Instead of sapphire-blue, the resulting 

 colour is a rich metallic green in general effect : though many 

 individual prismatic bodies show various other tints ; some, 

 which, it may be presumed, happen to interrupt tiie view of yellow 

 pigment only, being a pure yellow. It is evident that if, under 

 natural conditions, the prismatic bodies were associated with both 

 black and yellow pigment, manipulation of the latter would 

 achieve a very considerable range of coloration. 



' tTntersuch. Physiol. List. Seidelb, iv. 1882, Heft 3., 



