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A History of Infusoria, including the Desmidiacea and 

 Dlatomacecp, &c. By Andrew Pritchard, M. R. I. 

 Fourth Edition. Enlarged and revised by J. T. Arlidge, 

 W. Archer, J. Ralfs, W. C. Williamson^ and the 

 Author. Forty Plates, pp. U68. 



When a work has reached n fourth edition, it may be con- 

 sidered in most cases to have passed beyond the domain of the 

 reviewer ; and Pritchard's ' Infusoria^ has been so long Ijefore 

 the worldj and, as the number of editions through which it 

 has passed shows, so well appreciated by microscopical 

 observers, that it might now fairly be expected to have 

 escaped any further critical ordeal. But the fact is, that 

 although the old title, and a considerable part of the contents 

 of former editions, are retained, the present may, in all 

 essential respects, be regarded as a new and, to some extent, 

 an original work. As such, we cannot but congratulate the 

 world of microscopists upon its appearance. The names on 

 the title-page are sufficient guarantee for the value of the re- 

 spective portions they have contributed to the contents; and we 

 have no hesitation, after a careful survey, in saying that we 

 regard Mr. Pritchard^s work, in its present guise, as a valuable 

 contribution to science, and well calculated to afford to those 

 who are interested in the subjects upon which it treats a satis- 

 factory and lucid compendium of nearly all that recent 

 observations have brought to light. 



Nothing is more striking in the progress of Ijiological science 

 than the daily increasing extent to which the subdi\dsion of 

 labour is carried ; whilst, at the same time, for the advance of 

 real knowledge nothing has become more indispensable. The 

 indefatigable and continual labours of collectors and ob- 

 servers have so multiplied the objects of natural history in 

 all branches, that it is now quite impossible for any indi- 

 vidual, however acute his perceptive faculties, or however 

 retentive his memory, to embrace more than a very limited 

 range of subjects. This is obvious enough even in the case of 

 the higher and specifically less numerous classes of animals and 

 plants ; and in the lower, the multiplicity of forms is so vast, as 

 to render even extreme subdivision imperatively necessary for 

 their accurate study. And the same considerations apply in 

 their fullest force to those lowest forms of living organisms 

 which constitute more peculiarly the subjects of microscopic 

 study. We consequently find, that although Ehrenberg, but 

 a few years back, was able, like a second Linnaeus on a small 



