gnificance.

When we remember that the actions of the sympathetic nerves are almost,
if not entirely, reflex in character, we at once see the psychological
importance of this discovery. This fact makes the phenomenon of
tinctumutation an involuntary act on the part of the animal possessing
the chromatic function, and thus keeps inviolate the fundamental laws of
evolution, which, were the facts otherwise, would be broken.[101]

[101] This simple fact of involuntary action renders the sensual
nature of the function all the more apparent.--W.

By a series of experiments on frogs I have confirmed the conclusion of
Pouchet _in toto_, and have even solved, so I believe and unhesitatingly
assert, the puzzling problem of the physiological _modus operandi_ of
the wonderful phenomenon of tinctumutation.

For a very long time I believed that this function was a distinct sense,
and, five years ago, I set to work in search of the sense's centre.
After many dissections I found it (in the frog) lying immediately below
the optic centres and closely connected with them. Nerve-fibres of the
sympathetic can easily be traced and can be seen to penetrate this
centre. When this centre is artificially stimulated either with the
point of a needle or with a mild electric current, tinctumutation can be
incited at will.

Again, when this centre is destroyed (which can be done without injury
to the optic centres), the chromatophoric function ceases--the
phenomenon of tinctumutation is no longer observable.

That the sympathetic nerves are the carriers of the messages from the
optic nerve and the color-changing centre, can be demonstrated by other
means than by excision of the nerve. Atropine, to a certain extent,
paralyzes the sympathetic when given in sufficiently large doses, and
injections of this drug beneath the skin of a frog render the division
of the sympathetic unnecessary. The chromatophores will not respond to
light impressions if the animal be placed thoroughly under the influence
of atropine.

A large number of the lower animals possess the chromatophoric function.
Several years ago, I placed in a large cistern several specimens of gilt
catfish. This is a pond fish and is quite abundant throughout the middle
United States. It is of a beautiful golden yellow color on the belly and
sides, shading into a lustrous greenish yellow on the back and head.

Several months after these fish had been placed in the cistern, it
became