MUSEUM OF COMPARATIVE ZOOLOGY. 193 
EXPLANATION OF THE PLATE. 
Fig. 1. Pigmented area near the centre of the lateral line of adult Gasteros- 
teus, showing the upper and the lower layer of chromatophores fully 
expanded. 
Fig. 2. One of the chromatophores of the upper and the lower layer. The cell 
with expanded ramifications belongs to the upper layer. From the 
same area as those of Figure 1. 
Pigmented area of the same portion as that of Figure 1, taken from a fish 
which had been kept upon a bottom of white tiles, showing the con- 
tracted chromatophores. 
Fig. 4. Expanded surface chromatophores of a pigmented band on the flanks of 
a young Ctenolabrus, measuring about 5 mm. in length. 
Fig. 5. Expanded chromatophores of the opercular area of a young Ctenolabrus, 
somewhat older than the fish represented in Figure 4. 
Fig. 6. Large single chromatophore near the tail of a young Ctenolabrus of the 
age of Figure 4, fully expanded. 
Fig. 7. Chromatophores of a young Ctenolabrus taken from near the centre of 
the lateral line, showing the black cells contracted and closely packed 
together. 
Figs. 4-7. From young fishes caught in the tow-nets and subsequently kept on bot- 
toms of black and white tiles. 
Fig. 8. Pigmented area of flank of a gray Ctenolabrus, which had been kept on 
white tiles for twelve days. 
Fig. 9. A similar pigmented area from a young Ctenolabrus, which had been kept 
ona white tile bottom for ten days, and then placed for the same length 
of time on a black tile bottom. It had by no means recovered the dark 
appearance which the same area presented after being exposed to the 
action of light from a black tile for ten days. See Figure 16. 
Fig. 10. Pigmented area exposed to the action of the light from a white tile 
bottom for ten days. The black cells alone show changes; the col- 
ored cells do not differ from those of similar areas exposed upon a 
bottom of black tiles. 
Figs.11-15. Different views of the same pigmented area in several young speci- 
mens of Ctenolabrus, after being exposed to the action of the light 
upon a bottom of white tiles for about thirteen days. 
Fig. 16. The same pigmented area of a young Ctenolabrus, exposed upon a bot- 
tom of black tiles for ten days. The black pigment cells are intensely 
black, and the red cells somewhat more expanded than in Figure 10, 
and much less so than in the same areas exposed upon a bottom of 
white tiles for thirteen days. See Figures 11-16. 
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