According to the way in which their lumi nescent powers are used, animals May be divided, according to Watase, into three groups: (1) The photogenic substance is thrown out of the body and becomes luminous when it comes in contact with the oxygen of the air or water; this substance may he liquid as in the case of Pilo las and copepods, or fine granules as in Clue topterns. earthworm s. and myriapods. (2) In the seeond class, the photogenic material is never thrown out of the body. Oxidation is accom plished by the oxygen which is taken in with the air or the blood, as in the case of fireflies and glowworms. Such organisms can usually control their luminescence. (3) In the third group there are no special photogenic organs. The light-giv ing, material. however formed, accumulates along the course of muscle-fibres or other contracting organs and emits scintillating light at the time of protoplasmic contraction. In such forms as the Noctiluca, luminescence seems to occur in myriad; of fine points. In this form, too, myriads of fine strands of protoplasm are continually expanding and contracting throughout the prof o plasm of the animal. Heat and light are varia tions of the same radiant energy. They differ in degree, but not in kind. Ilence the heat and light producing particles in these luminescent organisms may be very similar. They may simply be variations of the same chemical sub stance. Infusoria, rhizopods, polyps, medusa, echinoderms, annelids, tunicates, mollusks, crus taceans, myriapods, and insects all have lumi nescent species. Noctiluca, one of the most bril liant, is an infusorian which occurs in certain parts of the ocean in prodigious numbers, delly fishes, ctenophores, and the tunicate Pyrosoma give out a considerable volume of glow when irri tated. Scolopendra among myriapods, and beetles, gnats, and May-flies among insects, are in air. Among insects there is a larva of a New Zealand Ily (Holotophila bun inosa) which emits light. Gnats of the family Chironombhe are sometimes entirely luminous with the exception of the wings.
case is recorded by Kane in his last voyage to the polar region of human luminescence, and a few other cases have been recorded by several good authorities where, especially a short time before death, the human body had a luminous appearance. It is interesting to note in this connection that the and permanent bril Haney of Noetiluca denotes•approaching dissolu tion." The light produced by protoplasm is the most economical light known, for all the energy is con verted into light, so that there is no loss in the form of heat or chemical rays. Langley and Very compared the light of insects with that of the sun by superimposing their spectra and found that the spectrum of the sun, With equal luminos ity, extends farther both toward the violet and the red ends of the spectrum, but the light of the Pyrophorus is more intense in the green region than sunlight. Hence both the heat-rays (the red) and the chemical rays (the blue) are prac tically absent from the spectrum of Pyrophorus.
Among insects, besides the well-known fireflies (Lampyrithe), luminosity is confined to a few other beetles, as certain Elaterid:e (Pyrophorus), an Indian buprestid (Ruprestis occ//«ta), and a telephorid larva. The so-called phosphorescence of insects and other animals is a greenish scintil lating or glowing light. The seat of the light is
the intensely luminous areas situated either in the abdomen or in the thorax (Pyrophorus). Each is a specialized portion of the fat-body. being a plate consisting of polygo nal cells, situated directly under the integument, and supplied with nerves and fine tracheal branches.
Lang says that the cells of this luminous organ secrete, under the control of the nervous sys tem, a substance which is burned during the ap pearance of the light; this combustion takes place by means of the oxygen conveyed to the cells of the luminous body by the tracheae, which branch profusely in it and break up into capil laries. Emery states that the males of Luciohl, display their light in two ways. When at night time they are active or flying the light is given out at short and regular intervals, causing the well-known sparkling or scintillating light. Lu ciola flying in the daytime, or injured, gives out a tolerably strong light, though not nearly reach ing the intensity of the sparkling light. In this case the light is constant, yet the phosphorescent plate is not luminous in its whole extent, but glows at different places as if phosphorescent clouds passed over it.
As to the use to the animal of this luminosity, it is generally supposed to allure the females, but Emery thinks it is a means of defense, or a warn ing or danger-signal against insectivorous noc turnal animals, such as bats, since when crushed the firefly (Lucio1a1 emits a disagreeable cab bage-like smell, though it has no acrid taste. The eggs of fireflies are luminous, but this is prob ably due to portions of the fat-body cells acci dentally adhering to the outside of the egg. The larvae are luminous at different ages. while the position of the luminous organs changes with age. In the larva of Pyrophorns before molting the light apparatus is situated only on the under side of the head and prothoracie segment. In larv•e 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. In the adult beetles there is a lumi nous spot on the under side of the first abdomi nal segment. but the greatest amount of light is produced by the vesicles on the hinder part of the protho•ax (Dubois).
BIBLIOGRAPHY. Verwo•n. General Physiology, Bibliography. Verwo•n. General Physiology, translated by F. G. Lee (London, 1899) ; Langley and Very, "On the Cheapest Form of Light." in mess Jour. Science, 3d series (New Haven, 1890 ) ; Pfifiger, various articles in Arch. f. a. ges. Physiol. (Berlin, 1S73, 187S, 1883, and 1884) ; Dubois, "Anatomie et physiologie comparees de la Pholade daetyle." in A finales dr l'Unirersuftj de Lyon, vol. ii. (Lyons, 18921; Watase. various papers in Biological Lectures at Wood's Hole (New York. 1S95 and 1898) ; Emery, suelningen fiber Luciola Italiea," in Zcits. f. wissens. Zool., vol. xi. (18541 ; "La Nee della Luciola osservata col microscopic)," in Bull. Soc. Ent. Ital. (1855) ; Dubois, "Contribu tion it Vehicle de la production de la lumiere par les titres vivants, Les Elaterides himineux." in Bull. Soc. Zool. France (Paris, 188G1; Wielo wiejsky, "Beitrhge zur Kenntniss der Lemehtor gane der Insekten," in Zool. Anzciger, Jahrg. xii. (Leipzig, 1859).