190 BULLETIN OF THE 
here and there an amoebiform thread extending from the central nu- 
cleus (Fig. 3). If the bleached specimens were kept continuously upon 
the white tile for five to six weeks, they apparently lost the faculty of 
regaining their original coloring. When removed to a background of 
black tiles, specimens which had been submitted to the action of the 
light of the white tiles for only from three to ten days regained to a 
great extent their original coloration, though never its primitive bril- 
liancy ; while the specimens which had been bleached for a longer time 
seemed to have become permanent albinos, or grayish lighter colored 
specimens, The pigment cells no longer expanded and contracted under 
the influence of varying conditions of intensity of light, as they do when 
they have not been too long subjected to one set of strong influences. 
Our common Ctenolabrus varies, as is well known, greatly in color- 
ation. But the conditions which bring about the differences described 
are seen only in the young from the time they hatch until they are not 
more than from about four to five months old. The shade of coloring 
is brought about by the greater or less development of the pigment 
cells, which assume either the form of a thin grayish film, with an 
annular nucleus, the film consisting of comparatively short, broad 
amobiform expansions, giving to the fish a gray appearance if spread 
uniformly over the surface, or of gray patches or bands if limited to 
special areas (Fig. 5). Should the black chromatophores be more con- 
centrated, and its offshoots thinner but more numerous, and packed 
together as they are in Figure 4, the young fish would appear to have 
a much darker tint, and from the reduction of these chromatophores to 
mere dots, with the presence only of the larger black chromatophores 
on the upper edge of the alimentary canal, and near the tail, the fish 
assumes an entirely different aspect, being comparatively transparent 
and colorless. 
Experiments made with the youngest stages of Ctenolabrus and of 
Platessa have shown the same results. A number of specimens of each 
species were picked out as soon as hatched, and placed respectively 
upon black and white tiles. The young of Ctenolabrus and of Platessa 
at these early stages have only black pigment cells, so that the effect of 
light is not complicated by the interference of other colored cells. 
After ten days, the young of Ctenolabrus placed upon the white 
tiles were found to develop only into practically colorless stages, such 
as are figured in Figures 1, 2, and 4 of Plate XIV. of the Young Osse- 
ous Fishes, Part III.,! while those which were placed upon black tiles 
1 Proc. Am. Acad., Vol. XVII. p. 271. 1882. 
