5IO THE INSECT WORLD. 



spontaneously or under the influence of artifical excitement. Some 

 chemical experiments have been made to ascertain the nature or the 

 composition of the humour which produces this strange effect ; but 

 up to this moment, they have only enabled us to discover that the 

 luminous action is more powerful in oxygen, and ceases in gases 

 incapable of supporting combustion. In the most common species, 

 the Lampyris noctiluca, or glow-worm, the phosphorescence is of a 

 greenish tint : it assumes at certain moments the brightness of white- 

 hot coal. 



The females have no wings, while the males have them, and 

 possess very well-developed elytra. The females resemble the 

 larvae much, only they have the head more conspicuous, and the 

 thorax buckler-shaped, like the male. The larvae feed on small 

 molluscs, hiding in the snails' shells, after having devoured the 

 inhabitant. They also possess the phosphorescent property in a less 

 degree than the adult females. The female pupa resembles the 

 larva ; the pupa of the male, on the contrary, has the wings folded 

 back under a thin skin. The perfect insect appears towards the 

 autumn. 



The Glow-worm (Lampyris noctiluca, Fig. 550) is of a brownish 

 yellow. It is common in England. In a kindred species, the 

 Lutiola Italica, the two sexes are winged, of a tawny-brown, and 

 equally phosphorescent. They are met with in great numbers in 

 Italy, and the lawns are covered with them. Other insects of this 

 family are without the faculty of emitting light ; as, for example, the 

 genus Lycus, of brilliant colours, which are met with in Africa and 

 India. One of the finest is the Lycus latissimus. 



Drilus is another genus, comprising insects of very singular 

 habits. The type is the Drilus flavescens. The male a quarter of 

 an inch long, black and hairy, with elytra of a testaceous yellow, and 

 with pectinated antennas for a long time was alone known. The 

 female from ten to fifteen times as large, without wings and elytra, 

 of a yellowish brown was not discovered till much later, having 

 apparently nothing in common with the male in shape or colour. 

 The metamorphoses of these curious insects are now perfectly under- 

 stood. Mielzinsky, a Polish naturalist established at Geneva, 

 found the Drilus in the larva state in the shell of the Helix nemoralis. 

 These larvae devour the snail whose dwelling they occupy, as do the 

 larvae of the Lampyris. Mielzinsky saw them emerge, but obtained 

 only females, which differed scarcely at all from the larvae from which 

 they proceeded. He made a separate genus of them, under the 

 denomination of Cochleoctonus, and called the species Vorax. Later, 



