POLYGASTRICA. 



containing putrefying vegetable matter, innumerable moving points 

 are visible, scarcely distinguishable except under the highest powers 

 of the microscope, but, when magnified to the utmost, assum- 

 ing the appearance represented at Jig. 16, 1 : these have been 

 termed Monads; and, as they F - lg 



may well be supposed to be 

 the smallest creatures in ex- 

 istence, have been regarded 

 as the limit of the animal 

 world ; their minuteness, in- 

 deed, is incalculable. Dr. 

 Ehrenberg * has described 

 monads which are not larger 

 than from ToW to T^O o of a 

 line, and which appeared to 

 be separated from each other 

 by intervals not greater than 

 their diameter. Each cubic 

 inch of the water in which 

 they are found must contain, 

 therefore, 800,000 millions of 

 these animalcules, estimating 

 them to occupy but one-fourth 

 of its space. A single drop, brought under the field of the micro- 

 scope, and not exceeding one cubic line in diameter, will there- 

 fore contain 500 millions, equal to the whole number of human 

 beings upon the surface of the globe. Well may the mind, 

 overwhelmed with wonder at such an astounding fact, launch 

 into visionary speculations when contemplating it ; and we are 

 little surprised to see the fertile imagination of Buffon figuring all 

 animal and vegetable bodies as composed of aggregations of these 

 living particles, believing them to be the primitive materials of 

 which organized substances are made up. 



(73.) The Proteus, (Am<ebaE.)Jig. 16, 2, is not frequently met 

 with, but affords a singular example of an acrite animal. It ap- 

 pears under a good glass to be an atom of transparent jelly, which 

 perpetually changes its form by contractions of different parts of its 

 body ; at one time being a roundish mass, then expanding into a linear 



* Ehrenberg's valuable researches concerning the Polygastrica are to be found in 

 the Transactions of the Berlin Academy, Abhandlungen der Academic von Berlin. 

 vols.68, 69, and 71. 



