70 ENTOMOLOGY. 



sensibly larger, and never smaller, than the females, and do 

 not generally pair with the females, until a week or fort- 

 night after emerging from the pupa, and until they have 

 assumed their proper masculine colors (Darwin's Descent of 

 Man, i. 337). 



The larvae are interesting creatures to keep alive in 

 aquaria, where their transformations can be watched, 

 especially if collected in the spring. Little is known re- 

 garding their habits, and any one who can spend the neces- 

 sary time and patience in rearing them, so as to trace up 

 the different stages from the larva to the dragon-fly, and 

 describe and accurately figure them, will do good service to 

 science. When about to cast its skin, a rent opens along 

 the back of the thorax, and the insect having fastened its 

 claws into some object at the bottom of the pool, it gradu- 

 ally works its ways out of the larva skin. When about to 

 change to the adult fly, the pupa climbs up some plant to 

 near the surface of the water, its back then yawns apart, and 

 from the rent the dragon-fly slowly emerges. For an hour 

 or more it remains torpid and listless, with its flabby, soft 

 wings remaining motionless. The fluids leave the surface, 

 the wings expand, the skin hardens and dries, the colors 

 appear, and the dragon-fly rises into the air. The colors of 

 dragon-flies are very striking, consisting of rich green, blue, 

 yellow, vermilion and metallic tints, and the sexes differ in 

 color. Certain dragon-flies appear to be attracted by par- 

 ticular colors, as the blue males of an Agrion were seen to 

 settle in numbers on the blue float of a fishing-line. The 

 males, in several genera, when they first emerge from the 

 pupa are colored exactly like the females; but in a short 

 time they assume a conspicuous milky-blue tint, owing to 

 the exudation of a kind of oil, soluble in ether and alcohol. 

 Certain species of Neurothemisare dimorphic, some females 

 having their wings netted as usual, while others have them 

 richly netted as in the males of the same species. In several 

 species of Agrion a certain number of individuals are of an 

 orange color. (Darwin's Descent of Man, i. 352.) 



