Page:Popular Science Monthly Volume 46.djvu/406

From Wikisource
Jump to navigation Jump to search
This page has been proofread, but needs to be validated.

two nerves running close to the vertebral column—the sympathetic nerves. 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 at once lost their power of contraction. Thus he proved that the sympathetic nerves were the transmitters of the optical message and not the cord. This discovery of Pouchet is, psychologically, of the greatest importance, though he failed to recognize it as such. He was satisfied with its anatomical and physiological importance. When we remember that the action of the sympathetic nerve is almost if not entirely reflex in character, we can see at once 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. By a series of experiments on newts and frogs I have confirmed the conclusions of Pouchet in toto. I have gone still further in demonstrating the fact that the sympathetic nerves are the conductors of the optical stimulus. Atropia, to a certain extent, paralyzes the sympathetic. Injections of this drug beneath the skin of a frog render the division of the sympathetic unnecessary. The chromatophores will not respond to light impression if the animal be placed under the influence of atropine.

A large number of the lower animals possess the chromatic function. Several years ago I placed in a large cistern several specimens of the gilt catfish. This is a pond fish and is quite abundant throughout the middle 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 necessary to clean it, and the fish were taken out. They were of a dirty drab color when taken out, but soon regained their vivid tints when placed in a white vessel containing clear water. They had evidently changed color in order to harmonize with the black walls and bottom of the cistern. Some katydids are marked tinctumutants. I took one from the dark foliage of an elm tree and placed her on the lighter colored foliage of a locust. She could be easily seen when first placed on the locust. In a few moments, however, she had faded to such an extent that she was scarcely noticeable. I have observed that hte larvæ of certain moths, beetles, and butterflies also possess the chromatic function. The chromatophores in the larva of Vanessa are quite abundant, and this grub is a remarkably successful tinctumutant. The power of changing color so as to resemble, in coloring, surrounding ob-