120 INSECT TRANSFORMATIONS. 



In the practical management of the eggs of the silk- 

 worm, Count Dandolo directs the temperature of the 

 stove-room to be 64° when they are tirst put in. 

 ^ The third day the temperature sliould be raised to 

 66°; the fourth day to 68°; the fit\li day to 71°; the 

 sixth day to 73°; the seventh day to 75°; the eighth 

 day to 77°; the ninth day to 80°; the tenth, eleventh, 

 and twelfth days to 82°. When the temperature of 

 the stove-room is raised to 7.5°, it is advantageous to 

 have two dishes, in which water may be poured, so as 

 to offer a surface of nearly four inches diameter. In 

 four days there will have taken place an evaporation 

 of nearly twelve ounces of water; the vapour, which 

 rises very slowly, moderates the dryness which might 

 occur in the stove-house, particularly during a north- 

 erly wind: very dry air is not favourable to the'devel- 

 opment of the silk-worm.'* Damp or stagnant air, 

 or sudden changes of temperature, either high or low, 

 are exceedingly injurious to the hatching of eggs. 



From some very curious experiments of Michelotti, 

 it appears that exposure to light is by no means favour- 

 able to the hatching of eggs This ingenious natural- 

 ist i .closed a number of eggs in glass vessels, admit- 

 ting the light to one series and excluding it from 

 another, similar in every other particular. The result 

 was, that few or none of the eggs exposed to light 

 were hatched, while those in the dark were almost all 

 fertile. He arrived at the same results in his experi- 

 ments upon vegetable seeds. "f Kirby and vSpence 

 justly remark, that these curious facts may account 

 for so many insects fastening their eggs to the under 

 sides of leaves, and may be the final cause of the 

 opaque horny texture of those exposed in lull day.^j] 



Among the singular circumstances in w4iich insects 

 differ from the larger animals, we may reckon that 



*■ Count Dandolo, on Silk- Worms, Eng. trans., p. 55. 



t Philosophical Mag., vol. ix, p. 244, f Introduc. iii, p. 77. 



