INSECTS. 125 
each side of the thorax, aad emit a vivid light visible even 
in broad daylight. 
Note.—The light of the common fire-fly (Lampyris) gives a spec- 
trum from which blue and violet are omitted. Jaeger, the naturalist, 
states that the Elaters were frequently the means of saving his life, 
by lighting his way out of the dense forests of St. Domingo. 
Fic. 154.—Diving-beetle (Dytiscus marginalis). g, grub, showing pincers. 
Diving-Beetles (Dytiscide),—These aquatic beetles 
(Fig. 154) are of an oval or rounded form, with the pos- 
terior legs fringed for swimming, and feet provided with 
suckers (Fig. 155). The larve are ferocious creatures, 
called water-tigers (Fig. 154, g), having flattened heads and 
scissor-like jaws, with which they capture small fishes, tad- 
poles, and insects. The body ends in a pair of respiratory 
tubes, that are thrust into the air. When ready to change, 
the larva creeps ashore, builds a round cell, and in five 
7 
