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172 influence by checking respiration in the way in which it causes the nerve to act upon the muscle in muscular motion." These remarks appear to harmonise with the principal facts which have been ascertained respecting this interesting phenomenon, and the nature of the substance by which it is produced. These facts are chiefly the following:—the light is subject to the will of the animal; it becomes more brilliant when its motions are violent; a certain degree of heat is necessary for its display, and its intensity increases up to 40° R. when it becomes extinct, as it likewise does when the cold is at 10° R.; oxygen renders it more brilliant for a short time, but soon extinguishes it; the same effect is produced more speedily by irrespirable gases, and by placing it in a vacuum; the phosphorescence soon disappears after the death of the animal, but can be restored by warm water, oil, or alcohol; galvanic electricity excites it; and, finally, when the insect is kept for some time in the dark, the luminosity disappears, but is restored by exposure to the light of the sun.

According to the observations of M. Morren, professor of botany in the University of Liege, as detailed by Lacordaire, the luminosity of the common European Lampyridæ is increased in brilliancy by the peculiar structure of the corneous envelope of the phosphorescent matter. It is stated to be merely a continuation of the general tegument, become much