PREFACE. 



IT is now some ten years since the author, then but a recruit in the ranks 

 of practical microscopists, elected to concentrate his attention upon the 

 group of organisms that form the subject of this treatise. At a very early 

 period of his investigations, formidable obstructions to substantial progress 

 in the course mapped out, presented themselves in connection not only 

 with the very backward condition of the literature of this country relating 

 to this topic, but by reason also of the exceedingly wide and scattered area 

 of Continental bibliography that had to be explored and sifted before it 

 was possible to arrive at any adequate idea of the state of contemporary 

 knowledge concerning almost any given type that might be the subject of 

 examination. It was the recognition of, and continual contact with these 

 difficulties that suggested to the author the advantages that would accrue 

 both to himself and all English-speaking microscopists, from the compilation 

 of a treatise, brought up to date, that should contain a concise description 

 of the innumerable species known to science whose descriptions were dis- 

 tributed throughout many scattered sources, and that led to the efforts, 

 now carried into execution, to supply this desideratum. 



It was in the first instance suggested that this Manual should be based 

 upon the same lines as the, at the time, only other English treatise devoted 

 to the subject, ' A History of the Infusoria/ by Andrew Pritchard, the fourth 

 and last edition of which was published so long since as the year 1861 ; 

 that it should include in a similar manner an account of the several distinct 

 groups of microscopical organisms known as the Rotifera, Desmidiaceae, 

 Diatomaceae, and other Protophytes which form, as being a reproduction 

 of Ehrenberg's ' Infusionsthiere/ so conspicuous a feature of Mr. Pritchard's 

 book. It soon became apparent, however, that to compass so compre- 

 hensive a task with any degree of efficiency would extend the size of this 

 treatise far beyond convenient limits, and that indeed more than sufficient 

 material for a work on the same scale as the one above-named had 

 accumulated in connection with the Infusoria in the most limited and 

 restricted sense as represented by the Flagellate, Ciliate, and Tentacu- 

 liferous Protozoa. 



Those readers and subscribers, therefore, who at first sight may 



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