416 THE MICROSCOPE. 



remarkable that the purest snow-water, caught in a cleai 

 glass vessel, and allowed to remain well corked, will, in 

 the course of two or three weeks, "be found to contain 

 Amoeba and Circomonas, but it rarely presents other forms 

 of animal life ; the vegetable matter then completes its 

 growth very slowly, gradually passes to Conferva, and for a 

 time no other change is seen to take place ; so that it is 

 painfully apparent that the atmosphere in which we live and 

 move and have our being is something more than a mixture 

 of gases, as apparently determined by chemical analysis. 



Fig. 219. 



1, Achnanfhidiwn coarotatum. 2, A. lineare. 3, Tryblionella gracillis. 4, 

 Amphitetras antediluviana. 5, 6, and 7, Orthosira spinosa. Front view, with 

 globular and oval foims. (Fossil Infusoria from Springfield, Barbadoes.) 



Ehrenberg's " Poly gastric Infusoria" have indeed under- 

 gone a complete revision : some have been degraded to the 

 vegetable kingdom, as the Desmidiacece, Volvocinece, &c., 

 whilst others have been advanced a step higher in the 

 animal series ; none having received so much attention from 

 microscopists, or excited so much controversy, as the Desmi- 

 diacece and Diatomacece. The first of these we have already 

 disposed of in :-nr remarks on the vegetable kingdom, 

 where we must be content to leave them for the present; 



