The position of the luminous organs changes with age. In the larvæ of Pyrophorus before moulting, according to Dubois, the luminous organs are situated only on the ventral side of the head and prothoracic segment. In larvæ of the second stage there are added three shining spots on each of the first eight abdominal segments, and a single luminous spot on the last segment. These spots are arranged in a linear series and thus form three luminous cords. In the adult beetles there is a luminous spot in the middle of the first abdominal sternite, but the greatest amount of light is produced by the two vesicles on the hinder part of the prothorax, the position of which varies according to the species.
LITERATURE ON PHOSPHORESCENCE
Peters, W. Ueber das Leuchten der Lampyris italica. (Müller’s Archiv f. Anatomie, 1841, pp. 229–233.)
Kölliker, A. Die Leuchtorgane von Lampyris, eine vorläufige Mittheilung. (Verhandl. d. phys. medizin. Gesellsch. Würzburg, 1857, viii, pp. 217–224.)
Schultze, Max. Ueber den Bau der Leuchtorgane der Männchen von Lampyris splendidula. (Sitzber. d. niederrhein. Gesellsch. f. Natur. u. Heilkunde zu Bonn, 1864, Sep. p. 7.)
—— Zur Kenntniss der Leuchtorgane von Lampyris splendidula. (Archiv f. mikroskop. Anat., 1865, i, pp. 124–137, 2 Taf.)
Wielowiejski, H. Ritter von. Studien über die Lampyriden. (Zeits. f. wissens. Zool., 1882, xxxvii, pp. 354–428, 2 Taf.)
Emery, Carlo. Untersuchungen über Luciola italica L. (Zeits. f. wissens. Zool., 1884, xl, pp. 338–355, 1 Taf.)
—— La luce della Luciola italica osservata col microscopio. (Bull. Soc. Ent. Ital. Anno xvii, 1885, pp. 351–355, 1 Taf.)
Wheeler, William Morton. Concerning the blood tissue of the Insecta, III; Psyche, vi, 1892, p. 255. (Structure of the light organ of Photuris pennsylvanica.)