146 CAROTINOIDS AND RELATED PIGMENTS 



various ways and also with structural blues and whites. As in birds 

 the various shades of brown are melanin combinations with reds and 

 yellows and the greens are combinations of yellow pigment and struc- 

 tural blues. The structural whites, however, do not appear to be 

 colloidal phenomena as in the case of birds, but are due to shiny 

 crystals of guanin. Another marked difference between the surface 

 colorations of birds and fishes is the deposition of the pigments in the 

 latter in chromatophors over which there is nervous control such that 

 a partial or complete contraction of the tissues makes it possible for 

 the animal to undergo marked changes in color. This physiological 

 phenomenon is shared by a number of other lower animals, both among 

 the vertebrates and invertebrates. One can find the whole subject 

 considered most exhaustively by Fuchs (1914). 



As in the case of birds this monograph can deal only with the red 

 and yellow pigments. It may be stated at the outset that a most 

 promising field for investigation from the point of view of our present 

 knowledge of carotinoids is offered by these pigments. No investiga- 

 tion whatever has been undertaken since the recent developments in 

 this field. However, there is no reasonable doubt that the yellow pig- 

 ments, at least, are carotinoids, either carotin or xanthophylls or 

 both. What is needed especially, besides an exact determination of 

 the carotinoid character of the yellow pigments, is a study of the red 

 pigments whose solubilities and color reactions with the mineral acids 

 are those of the carotinoids, but which have failed to show absorption 

 bands in the hands of previous investigators. 



De Merejowski (1881) first called attention to a rather widespread 

 occurrence of the red pigment in fishes, under the name of tetronery- 

 thrine. He later (1883) enumerated some 20 species in which he had 

 found the pigment, in this paper adopting Bogdanow's (1858) name 

 zoonerythrine. No spectroscopic observations were made. The orange 

 color in the usual fat solvents was noted, as well as the fiery red color 

 in CS 2 , the color reactions by the strong mineral acids, and the bleach- 

 ing in the air and sunlight. It is interesting that de Merejowski ex- 

 pressed the opinion that the same pigment caused the color of carrots, 

 tomatoes and pimentoes. Carotin, according to him, it may be noted, 

 is a water-soluble pigment from carrots and tomatoes. 



Krukenberg (1881 a) first noticed the red zoonerythrine in fishes in 

 the tailfin of Luvarus imperialis, the microscope showing the red 

 granular deposits in the epithelial cells. On extraction with fat sol- 

 vents or hot alcohol the pigment confirmed the observations of 



