altogether an exceptional form, being destitute of wings in both sexes, and possessed of only very feeble light-giving powers, and we have, moreover, very little real knowledge as to its natural history; it is said {250}that the female is of the utmost rarity, though the male is not uncommon. The nature of the luminosity of _Lampyris_ has given rise to many contradictory statements; the light looks somewhat like that given off by phosphorus, and is frequently spoken of as phosphorescence; but luminescence is a better term. The egg, larva, pupa, and male are luminous as well as the female (at any rate in _L. noctiluca_); the luminescence is, however, most marked in the female imago, in which it is concentrated near the extremity of the abdomen; here there are two strata of cells, and many fine capillary tracheae are scattered through the luminous substance. Wielowiejski concludes that the light-producing power is inherent in the cells of the luminous organ, and is produced by the slow oxidation of a substance formed under the influence of the nervous system. The cells are considered to be essentially similar to those of the fat-body.[126] The luminescence of Lampyridae is very intermittent, that is to say, it is subject to rapid diminutions and increases of its brilliancy; various reasons have been assigned for this, but all are guesses, and all that can be said is that the changes are possibly due to diminution or increase of the air-supply in the luminous organ, but of the way in which this is controlled there seems to be no evidence. Considerable difference of opinion has existed as to the luminescence of the eggs of _Lampyris_. If it exist in the matter contained in the egg, it is evident that it is independent of the existence of tracheae or of a nervous system. Newport and others believed that the light given by the egg depended merely on matter on its exterior. The observations of Dubois[127] show, however, that it exists in the matter in the egg; he has even found it in the interior of eggs that had been deposited unfertilised.