— v^, 



{uu LIBRARY j. J 



PREFACE. 



Special interest has always been taken by man in the structure and 

 development of the minute forms of life, whether animal or vegetable : 

 in this volume I propose to lay before the reader a resume of the 

 present state of our knowledge of the multitude of K^dng beings called 

 Infusoria. This term_, as employed by Professor Ehrenberg of 

 Berlin^ includes a wide range both of animal and vegetable life; 

 while it is now restricted by other naturalists to the Protozoa^ and, 

 in the works recently commenced by Dr. Stein and MM. Claparede 

 and Lachmann, to the ciliated members of that group. 



The former editions of this work having included a Histoiy of the 

 Bacillaria, Phytozoa, Protozoa (under the name Polygastrica), and of 

 the Rotatoria, it is incumbent on me to retain these groups, though 

 the researches of late years have so extended our acquaintance with 

 them that much difficulty has been felt in the attempt to comprise 

 the whole in a single volume, so necessary for a practical manual. 



The successful investigation of this department of Natural History 

 arose mainly from the improvement of the microscope consequent 

 upon the discoveries of "Test Objects'^ and "penetrating power/^ 

 the latter depending upon " angular aperture/^ — discoveries which 

 my colleague the late Dr. Goring and myself had the pleasure of 

 presenting to the public. The microscope, having become thereby a 

 reliable instrument, has revealed to us the true forms and structure of 

 these beings. 



Part I. is devoted to a General History of the several more or less 

 natural groups of Infusoria: it contains also the observations and 

 opinions of British and Continental naturalists on their nature, 

 structure, functions, and classification. The foreign writings on 

 these subjects are so voluminous that even an abstract of them has 

 increased this part of the work much beyond what it occupied in 



