20 THE ZOOLOGIST. 
the well-known fact that Salmon, &c., from dirty water are often 
pale and very silvery. One would rather expect that darkness 
would give rise to the same stimulus as a dark background, and 
the reflex would be an expansion of the chromatophores, or 
colour-cells, and so a darkening of the body. Perhaps in dark- 
ness there is no colour suggestion and the chromatophores 
receive no stimulus, and their contraction indicates a state of 
rest. This paleness at night or in the dark agrees well with the 
general rule of dull colours for nocturnal animals. Fishes which 
have died from suffocation, due to foulness or lack of oxygen in 
the water, are nearly always very pale; fishes which die at night 
are paler than those which die in daylight. On the side on 
which a freshly killed fish is laid the chromatophores contract 
and it may become almost white. Ifa freshly killed fish is laid 
on a erating, the lower side, after a while, will be found to be 
banded—pale where the bars of the grating pressed and dark 
elsewhere. If too long a time is not allowed to elapse and the 
fish is moved, so that the dark bands lie on the bars and the 
pale ones between them, then the chromatophores will react and 
the pale areas will darken, and vice versa, though not to such a 
marked extent as at first. This second reaction may be possible 
about forty minutes after death in a Cod. 
Mr. Cunningham has made similar observations, and has 
shown that this paleness at places of contact with other objects, 
which explains the marbled appearance of fish which have been 
packed for market, is due to pressure, and not to the exclusion 
of light, for on laying a glass slip on a piece of fresh fish “the 
chromatophores under the cover-glass contracted, while those in 
the uncovered skin remain expanded.”* The chromatophores, 
then, may remain alive after the death of the fish to which they 
belong, and retain their ability to respond to physical irritation ; 
they also respond to chemical irritation. In December, 1911, 
I took some pieces from the side of a Cod, three hours after it 
was caught, where the chromatophores were contracted owing to 
pressure, and bathed them with 5-1 per cent. formalin, and found 
the chromatophores expanded considerably in less than three 
minutes. Physical irritation produced practically no result, and 
light none. 
* * Philosophical Transactions,’ 1894, ‘‘ On the Coloration of the Skin of 
Fishes, especially of Pleuronectide,” Cunningham and MacMunn. 
