100 STATES OF INSECTS. 



once mentioned in this letter, are first mouse-col oured, 

 then they assume a reddish hue, and lastly a blackish 

 one. Those of the gnat from white in a short time as- 

 sume a shade of green, in a few hours they are entirely 

 green, and at length become gray a . Those of the silk- 

 worm, which at first are of a yellow or sulphur colour, 

 acquire a violet shade. The eggs of that rare moth En- 

 dromis versicolor, are at first sulphur-coloured, then 

 green, next rose-coloured, and lastly blackish. The 

 colour of almost all eggs changes when they are near 

 hatching; but this change depends more frequently upon 

 the colour of the included larva, which appears through 

 the transparent shell of the egg, than upon any actual 

 alteration in the egg itself. 



viii. Period of hatching. The general rule for the 

 hatching of the eggs of insects is the absorption by the 

 embryo of all the superabundant moisture included in 

 them ; but the time varies according to the state of the 

 atmosphere, to the action of which they are subjected. 

 Like those of other animals, they require a certain degree 

 of heat for the due evolution of the included larva. This 

 heat in much the greater number of instances is derived 

 from the temperature of the air, but often also from 

 other sources. The eggs of the gad-fly tribe are hatched 

 principally by the heat of the body of the animal to which 

 they are committed ; and doubtless the vital heat of va- 

 rious larvae, small as it may be, must contribute some- 

 thing to the hatching of the eggs deposited in them by 

 various Ichneumons. In the fermenting bark in which the 

 instinct of the rhinoceros beetles (Oryctes nasicornis &c.) 

 a Reaum. iv. 617- 



