CHAP. III. 



<<>F THE CHANGES INDUCED ON THE 

 AIR BY THE RESPIRATION OF INSECTS, 

 WORMS, FISHES, AND AMPHIBIOUS ANI- 

 MALS. 



48. JL o the commencement of living action 

 in vegetables, the presence of water (1. 23.) has been 

 shewn to be essentially necessary, and among several 

 inferior animal beings, its operation is equally striking 

 and apparent. The ova of innumerable tribes of ani- 

 mals, some of which afterwards inhabit the air, are 

 deposited in water, and undergo their various stages 

 of evolution only while exposed to the influence of 

 that necessary fluid. Neither is its agency confined 

 to the earliest states of existence, nor to those animals 

 which i may be properly called aquatic ; for examples 

 abound, where its operation extends through every 

 period of life, and among animals which reside whol- 

 ly in the air. Snails in their shells have been thrown 

 into a drawer, and lain by for fifteen years ; but reco- 



