FOOT — ON ANIMAL LUMINOSITY. 53 



The Coleopterous order includes the principal examples of phospho- 

 rescence, — the glowworms and the fireflies; both sets of insects (not- 

 withstanding their names) are beetles of the same Elater family ; the 

 most brilliant fireflies are inhabitants of the hot and temperate regions 

 of America. The glowworms are found in England, Fiance, Germany, 

 Italy, and other parts of Europe. The glowworms belong to the 

 genus Lampyris, of which there are about two hundred species all more 

 or less luminous : of the genus Elater, to which the firefly belongs, there 

 are at least seventy species, and probably many more, with both sexes 

 equally luminous. The word glowworm has arisen from the ver- 

 miform aspect of the female of the British species, Lampyris noctiluca, 

 which is apterous and not very locomotive. Aristotle was aware of 

 this fact, as he says — ants for example are both winged and apterous, 

 and so is the glowworm.* In other continental species both sexes are 

 winged. The males of the British species are but feebly luminous, and 

 that only at the pairing season ; those of the continental and foreign 

 species are phosphorescent at all times. The luminous organs of the 

 various species of Lampyris are of a special nature and well defined, 

 not to be confounded with the intervisceral adipose substance, and 

 present a determinate form, size, and position ; presenting in the 

 females of L. splendidula (the German species) four or five pairs 

 of lateral organs of the form of flattened globules, situated on the 

 abdominal segments from the first to the sixth rings. The luminous 

 organs consist of an investing membrane enclosing a parenchyma of 

 cells, trachea3 or air tubes, and nerves ; the cells are of two kinds, 

 white and pale, and it is in the contents of the pale cells the proper 

 luminous substance resides ; it corresponds in its microscopical reactions 

 with an albuminous material, but owing to the extremely minute quan- 

 tity of the substance which can be obtained, it has been impossible, as 

 yet, to subject it to a more satisfactory chemical examination. All 

 endeavours to detect the presence of phosphorus in the luminous or- 

 gans have been fruitless. The organs of thirty males' of L. Splendidula 

 were treated with sulphuret of carbon, and when this was allowed to 

 evaporate on blotting paper no luminosity was evident, nor was the 

 paper charred. When organs which have been isolated by dissection 

 are treated with nitrate of silver no black precipitate is formed. The 

 luminosity is dependent upon the will of the beetle, and exists by day 

 as well as at night, though very frequently absent in the day time, 

 simply from the fact that these insects are nocturnal in their habits, 

 and usually lie concealed in the dark during the day. Many irritants 

 exercise an influence upon the production of the light, but the most 

 powerful excitant is caustic potash, in all degrees of concentration, 

 from 7 to 50 per cent. Luminous glowworms, especially the females, 

 moistened with a solution of salt, placed with the cephalic and caudal 

 extremities on the cushions of Du Bois's current apparatus, have de- 



Hist. An.," lib. iv., cap. 3. 



