Page:The New International Encyclopædia 1st ed. v. 12.djvu/602

* LUMINOSITY OF ANIMALS. 636 LUMINOSITY OF ANIMALS. tlic cell, foniKMl as the result of inetal)iilism in the cell, ami in the process of its formation iden- tical with that known as secretion. He says fur- ther that the process of secretion does not neces- sarily imply the existence of a gland; the funda- mental jiruccss of secretion may he carried out by an isolated single cell just as well as by thou- sands of similarly constituted gland-cells. For the luminous aiijiaratus of deep-sea lishes, see LANTiiH.-Fi.sii and the accompanying plates. The emission of light by living substances is widespread. It is an especially significant fact that, of the wonderful pelagic animals whose delicate transparent bodies occupy the upper strata of the sea and lloat about as plankton, al- most all possess luminous power. Associated with this fact is the presumption that the lumi- nous capacity of living substances is possildy nuich wider s]ircad than is realized, tlial we do not see the light because the organisms are not trans- parent, or because the production is too feeble to allow the light to be seen through thick body- layers; indeed, it is not impossible that in our own bodies certain cells may be photogenic. In most cases, as in luminous insects, N'erworn says, the power of emitting light is a peculiarity spe- cially perfected by selection, and possesses its own "significance for the life of the animals in question. In pelagic marine animals, also, such a signiticancp is certainly present ; as a rule, these animals emit light suddenly and only upon stimu- lation, and hence it may be supposed that the light serves as a means of frightening enemies. Luminescence is a phencnnenon common both to animals and plants. Thus certain bacteria that live in sea-water, or those of putrefaction, such as Bacterium phoxjihoresccns, which lives on dead flesh, cause luminescence. At least two kinds of these bacteria are known to produce a blue light, anil one a greenish light. It is easy to make artificial cultures of these forms so as to study their growth and activities. Certain mushrooms of the genus Agaricus, which grow upon wood and cause its decomposition, are also luminescent. The blossoms of nasturtium, mari- gold, poppy, and other plants, and even the leaves, have been observed to emit light occa- sionally. Possibly the light in the latter cases is of electrical nature. According to the way in which their lumi- nescent powers are used, animals may be divided, according to Watase, into three groups: (I) 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 be liquid as in the case of Pho- las and copejKxls, or fine granules as in Chse- topterus. earthworms, and myriapods. (2) In the second 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 firefiies and glowworms. Sucli organisms can nsiially control their luminescence. (3) In the third group there are no special photogenic organs. The liglitgiv- ing material, however formed, accinnulates 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 myriads of fine points. In this form. too. myriads of fine strands of protoplasm are continually expanding and contracting throughout the proto- plasm of the animal. Heat and light are varia- tions of the same radiant energy. They differ in degree, but not in kind. Hence the heat and liglit producing particles in these luminescent organisms may be very similar. They may simply be variations of the same chemical sub- stance. Infusoria, rhizopods, polyps, medusir, eehinodcrms, annelids, tunieates, moUusks, 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 prodigiims immbers. .lelly- fishes, ctenophores, and the tunicate Pyrosonia give out a considerable volume of glow when irri- tated. Scolopendra among m3'riapods, and beetles, gnats, and JIay-llies among insects, are luminous in air. Among insects there is a larva of a New Zealand fly {lioUiopliiln liiniinosd) which emits light. Gnats of the family GhironomidiC arc^ sometimes entirely luminous with the exception of the wings. A case is recorded by Kane in his last voya,L;<' to the polar region of human luminescence, and a few other cases have been recorded by several good authorities whei'c, especially a short time before death, the human body bad a luminous appearance. It is interesting to note in tin- connection that the "steady and permanent bril- liancy of Noctiluca denotes approaching dissolu- tion." The light produced by proto])lasm 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 tli' Pyrophorus is more intense in the green rcgii ii than sunlight. Hence both the heat-rays (the red) and the chemical rays (the blue) arc prac- tically absent from the spectrum of Pyrophoru-^. Among insects, besides the well-known fireflies (Lampyridne), luminosity is confined to a few other beetles, as certain Klaterid;e (Pyrophorus). an Indian buprestid (Btiprrstis orrlhitn), 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 LDMINOna ORGANS. 1. Section tlirouph end of body of male flreflj (Luciolnh ii. dorwal layer; v. ventral layei- of the luiriiiiouH plate; s. skin. 2. Ventral layer isolated; tr, traehea; j), parencliyiiif cell; c, capillary trachea; w, coapulnni. 3. A tracheal stem. 4. A part of No. 3, more hif^lUy magnified. (After Emery.) the intensely luminous areas situated either in the abdomen (Lampyrid.ne), or in the thorax (Pyrophorus). Each is a specialized portion of the fat-body, being a plate consisting of polygo- nal cellsj situated directly under the integument,