ELATERIDAE FIRE-FLIES 259 



The earliest European travellers in the Kew World were so im- 

 pressed by these Insects that descriptions of their wondi-ous display 

 occupy a prominent position in the accounts of writers like Oviedo, 

 whose works ai-e nearly 400 years old. Only one of the species 

 has, however, been investigated. P. noctilue-us is one of the most 

 abundant and largest of the Pyrophorus, and possesses on each side 

 of the thorax a round polished space from which light is given 

 forth ; these are the organs called eyes by the older writers. 

 Besides these two eye-like lamps the Insect possesses a third 

 source of light situate at the base of the ventral surface of the 

 abdomen ; there is no trace of this latter lamp when the Insect 

 is in repose ; but when on the wing the abdomen is bent away from 

 the breast, and then this source of light is exposed ; hence, when 

 flying, this central luminous body can be alternately displayed 

 and concealed by means of slight movements of the abdomen. 

 The young larva of P. noctilucus is luminous, having a light- 

 giving centre at the junction of the head and thorax ; the older 

 larva has also numerous luminous points along the sides of the 

 body near the spiracles. It is remarkable that there should 

 be three successive seats of luminescence in the life of the same 

 individual. The eggs too are said to be luminous. The light 

 given off by these Insects is extremely pleasing, and is used by 

 the natives on nocturnal excursions, and by the women for orna- 

 ment. The structure of the light-organs is essentially similar 

 to that of the Lampyridae. The light is said to be the most 

 economical known ; all the energy that is used being converted 

 into light, without any waste by the formation of heat or 

 chemical rays. The subject has been investigated by Dubois,^ who 

 comes, however, to conclusions as to the physiology of the 

 luminous processes different from those that have been reached 

 by "Wielowiejski and others in their investigations on Glow- 

 worms. He considers that the light is produced by the reactions 

 of two special substances, luciferase and luciferine. Luciferase 

 is of the nature of an enzyme, and exists only in the luminous 

 organs, in the form, it is supposed, of extremely minute granules. 

 Luciferine exists in the blood ; and the light is actually evoked 

 by the entry of blood into the luminous organ. 



"We have given to this family the extension assigned to it by 



' "Les Elaterides lumineux," Bull. Soc. Zool. France, xi. 1886; also ief07is 

 cle Physioloyie ginirale, Paris, 1898, and C.R. Ac. Sci. cxxiii. 1896, p. 653. 



