258 
abundantly supplied with food *. He discovered al- 
so, that rhey soon perished in nitrogen and hydrogen 
gases ; that oxygen gas was necessary to support 
their life, and was consumed by their respiration ; 
and that a quantity of carbonic acid was produced. 
The cabbage and silk- worm caterpillars consumed, 
more or less completely, the oxygen gas of the air, 
and produced carbonic acid. The more vigorous 
and active they were, the more oxygen they consum- 
ed. In a high temperature, also, they consumed 
more than in a low one ; and when the temperature 
fell to zero, they then produced no change whatever 
in the air employed f. He found, likewise, the lar- 
vae of the dragon-fly, ;md of other aquatic insects, to 
require the presence of oxygen, in the water in which 
they lived, to consume it by the exercise of their 
living functions, and to form carbonic acid *. 
546. If, farther, we follow the larva to its chry- 
salis or pupa state, it will be found still to require 
the presence of the same agents, to enable it to go 
through its series of successive changes. The influ- 
ence of heat, in carrying forward these changes, is 
well illustrated by some experiments of M. de Reau- 
mur. That celebrated naturalist placed the pupa^ 
of many species of insects in a green house, and the 
butterflies appeared in the middle of winter, some in 
ten or twelve days, others in three weeks, and others 
at a later period, corresponding to the earlier or la- 
ter periods at which they naturally appear in the sum- 
* Tracts, &c. p. 227. 
t Rapports de 1'air, c. t. i. p. 17. et seq. J Ibid. p. 7?. 
