r, no matter how bright and
varied they were. The deductions drawn from these experiments are not to
be controverted or denied. The chromatophores are influenced by light
reflected from objects and transmitted _via_ the optic nerve to the brain;
from this organ the impression or irritation goes to the nerve governing
the contractile fibres of these pigment-holding glands.[98]

[98] Karl Semper, _Animal Life_, p. 95.

Pouchet followed Lister, and confirmed his conclusion by experiments on
fishes and crabs. He remarked that the plaice--a fish with a white
under-surface and a party-colored back--had the chromatophoric function
highly developed. Among a number of specimens which appeared pale on the
white, sandy bottom, he met "one single dark-colored fish, in which, of
course, the chromatophores must have been in a state of relaxation; and
this specimen was as distinct from its companions as from the bottom of
the aquarium. Closer investigation proved that the creature was totally
blind,[99] and thus incapable of assuming the color of the objects
around it, the eyes being unable to act as a medium of communication
between them and the chromatophores of the skin."[100] Thus far Pouchet
had only confirmed Lister's observations, although it is highly probable
that he was unaware of Lister's experiments. But he went a step further.
There are two ways in which cerebral impressions may be transmitted from
the brain to the skin: one, by way of the spinal cord and the pairs of
nerves arising from it and known as spinal nerves; the other, by two
nerves running close to the vertebral column--the sympathetic nerves.

[99] Mr. Gordon Rett has recently called my attention to a blind
"angel fish" which shows, most conspicuously, a lack of
tinctumutation. This fish was made blind for experimental
purposes.--W.

[100] Karl Semper, _Animal Life_, pp. 95, 96.

Pouchet cut the spinal cord close to the brain, yet the chromatophores
still responded to light impression, showing that they did not receive
the message through the cord and spinal nerves. He then divided the
sympathetic nerves, and the chromatophores lost at once the power of
contraction; he thus demonstrated that the sympathetic nerves were the
transmitters of the optical message, and not the cord.

This discovery of Pouchet is, psychologically, of great importance,
though he failed to recognize it as such. He was satisfied with its
anatomical and physiological si