312 Notice of Ehrenberg's Memoir on Microscopic Life. 



phosis of the older rocks, as the minutest forms must most easily be 

 destroyed. 



19. The opinion of some modern naturalists, that the species of ani- 

 mal organisms by increasing weakness gradually lose the organic con- 

 stitution, (durch wachsende Schwache der organischen Constitution 

 aufzehren,) is not confirmed by the smallest forms, either in Europe 

 or America, but on the contrary there occur also in America certain 

 forms which, since a period long anterior to the historic epoch, and in 

 all climates, have perfectly preserved the same characters. 



20. The sport of plastic nature, with pleasing changes of form, (mit 

 beliebigem Formen-Wechsel,) does not occur, even with the minutest 

 forms, any where on the western continent, whether at the equator or 

 the poles ; but it has been proved that on both hemispheres and from 

 pole to pole, there exists a group of forms which, with characters un- 

 changed from the chalk formation to the present time, have played a 

 great part as similar building-stones in the structure of the surface of 

 the earth. 



21. From the rapid and great increase of this knowledge of an inde- 

 pendent deep-working life in the smallest space, it follows that this field. 

 of research cannot be unworthy of the best efforts ; and if it is not 

 always equally and quickly productive, or if it may be more agreeable 

 with easier speculation, and rather in poetic sport, than seriously to pen- 

 etrate into the Remote, yet the only scientific and remunerating method 

 is by slow and sure steps, and under the check of careful and therefore 

 laborious research, to approach the goal which excites the mind of all 

 thinking men of all generations, and will interest all generations yet 

 to come. 



Part VII, contains the explanation of the Plates, which are four 

 in number. These are large and beautifully executed, and con- 

 tain seven hundred figures, including three hundred and twenty 

 five of the recent minute organisms from all zones of America. 

 The fossil species are omitted on account of their number, but 

 Ehrenberg states that they are already engraved for a larger work, 

 which will soon be published. He also states, that nearly all the 

 figures are drawn from prepared specimens which he still retains 

 as a durable collection which can be employed for unlimited 

 comparisons in future. 



In concluding our notice of this valuable paper, we cannot but 

 remark, that although the results already obtained are certainly 

 most important, and although Ehrenberg has made the best pos- 

 sible use of the materials in his possession, yet much remains to 

 be done, (as no one knows better than Ehrenberg himself,) before 



