418 PHYSIOLOGICAL LIGHT. 



This species mnabits central Europe and becomes luminous in autumn. 

 While walking or when stimulated its teguments transude a granulose, 

 viscous liquid that emits for some moments a greenish luster. Some- 

 times there is no cutaneous excretion and the entire body of the ani- 

 mal is illuminated, except the head. The Orya barbarica also, which 

 inhabits Algeria, may, under the influence of pressure and contact, dis- 

 charge from its abdominal, tegumentary pores a viscous liquor, insolu- 

 ble in alcohol, which solidifies rapidly, giving out at the same time a 

 greenish-blue light. The recent study of this secretion has given me 

 important information as to the intimate mechanism of photogeny. 



III. 



The most resplendent of all animals are insects, of which class the 

 glowworm, beloved of the poets, is one of the most brilliant exam- 

 ples. Among the thirteen orders of this class, there are but three that 

 contain species to which the photogenic power may be with certainty 

 attributed, viz, the Coleoptera, the Diptera, and the Thysanura. 



In certain continental localities the soil has been seen to become 

 luminous, like the sand of the sea which contains Noctilucce, on account 

 of the presence of quite minute insects belonging to the order Thysa- 

 nura, family Poduridcc, genus Lipura (fig. 2, Lipura noctiluca), that 

 are not more than 2 or 3 millimeters in length. I know of but one 

 photogenic species; this much resembles Lipura ambulans, if it is not 

 identical with it, but I prefer to call it Lipura noctiluca. 



Such species are also rare among the Diptera, the luminosity of the 

 antennae of the Thyreophora cynophila, a fly which lives in charnel 

 houses, being probably the result of its habitat. The function may, 

 however, be properly ascribed to the larvae and nymphee of Ceratoplatus 

 sesioides. There is also found in the Sea of Aral certain species of 

 CMronimus, which shine like small, dull stars. Certain analogous 

 phenomena have been noticed in Culex and Tipula. 



The most beautiful luminous insects are incontestably among the 

 Coleoptera, confined to the two related families of Malacodermidcv and 

 Elateridcc, of which the best known are the Luciola italica, the Lampyra 

 noctiluca or glowworm, and the Pyrophorus, commonly known under 

 the name cucuyos. 



The photogenic property appears in the egg of the glowworm (Lam- 

 pyra), even while it is contained in the ovary before fecundation ; in 

 the fertilized eggs it persists till the hatching of the larva. In these 

 centrolecithal eggs we find very early the blastoderm represented by a 

 single layer of large, polyhedric cells inclosing numerous rounded 

 granulations and possessing the same characteristics as those which 

 are again met with later in the luminous organs of the adult and the 

 larva. At the moment of hatching, in the larva of the first stage, the 

 luminous appearance shows itself in the form of two small, yellowish, 

 ovoid bodies situated on the sides of the penultimate ring. 



