POLYGASTRIC ANIMALCULES. METEORIC PAPER. 553 



scarcely any situation, in which we cannot find some traces of 

 their existence. Although they may be found, with the most 

 certainty, in infusions of decomposing organised matter (whence 

 their name Infusoria is derived), they are, as already stated, 

 diffused in greater or less degree, through almost all the fluid 

 masses upon the earth's surface ; and thus the animalcules found 

 in such infusions, may be regarded as but a minute specimen of 

 those at present existing in the waters, which cover so large a por- 

 tion of our globe. But they are not confined to a fluid medium. 

 There are many species whose natural habitation is mud ; and 

 others which aggregate together in masses, so as themselves to 

 form a kind of earth, which only requires a moderate amount of 

 moisture to preserve them alive. The extraordinary discoveries 

 of Ehrenberg, presently to be mentioned, in regard to the exist- 

 ence of the remains of Polygastrica in a fossil state, led him to 

 make a series of experiments upon their production in this 

 curious condition ; and he has fully succeeded in manufacturing 

 living earth, in large quantities. This corresponds precisely with 

 the Tripoli which occurs as a mineral in large beds, and which 

 is important to Man from its use in the arts ; and, according to 

 Ehrenberg, a small rise in the price of Tripoli would make it worth 

 while to manufacture it from the living animals, as an article of 

 commerce. There are many species which are capable of main- 

 taining a torpid existence, in earth dried up by the summer sun ; 

 and they are thus raised into the air, in countless myriads, in 

 the form of the most finely-divided dust. Perhaps if received 

 into a moist atmosphere, they may even revive and grow under 

 these circumstances ; for they are sometimes deposited again in 

 large masses. In 1687? a great quantity of a black paper-like 

 substance fell, with a violent snow-storm, from the atmosphere 

 in Courland. A portion of this substance, preserved in the 

 Berlin Museum, has been microscopically examined by Ehren- 

 berg ; and has found it to consist entirely of an organic mass of 

 Conferva^ matted together, and including twenty-nine species 

 of Infusoria, all of which occur in the neighbourhood of Berlin. 

 It is not unlikely, however, that this mass was originally formed 

 at the surface of a marsh, and was raised altogether by a storm ; 



