X PKEFACE TO THE SEVENTH EDITION 



lamented Dr. H. B. BRADY, F.R.S., I am under obligation for 

 valuable suggestions regarding the Foraminifera. 



From Dr. HUDSON I have received cordial aid in dealing with 

 his special subject, the Rotifera ; and to Mr. ALBERT MICHAEL I am 

 under equal obligation for his assistance in regard to the Acarina. 



Mr. W. T. SUFFOLK gave me his most welcome judgment and 

 advice regarding my chapter on Mounting, and I received also the 

 suggestions of Mr. A. COLE with much pleasure and advantage. 

 I have received help from Dr. A. HILL, of Downing College, 

 Cambridge, and from Professor J. N. LANGLEY, of Trinity College, 

 Cambridge from both of whom special processes of preparation 

 for histological work were sent. 



Mr. FRANK CRISP, with characteristic generosity, aided me much 

 by suggestions of special and practical value ; and Mr. JOHN MAYALL, 

 jun., the present Secretary of the Royal Microscopical Society, has 

 been untiring in his willingness to furnish the aid which his influence 

 was able to secure. 



To Professor W. HICKS, F.R.S., Principal of Firth College, 

 Sheffield, I am indebted for the revision of special sheets ; so also I 

 owe acknowledgments to Dr. HENRY CLIFTON SORBY, F.R.S., and to 

 Dr. GROVES, as well as to others, whose suggestions, advice, or con- 

 firmation of my judgments have been much esteemed ; and prominent 

 amongst these are Professor ALFRED W. BENNETT, B.Sc., and Professor 

 F. JEFFREY BELL, M.A., whose constant advice in their departments 

 of Biology I have received throughout ; while in Micro-geological 

 subjects I have been aided by the suggestions and experience of 

 Professor J. SHEARSON HYLAND, D.Sc. 



It will be observed that every endeavour has been made to 

 bring each of the many subjects discussed in this book into conformity 

 with the most recent knowledge of experts. Many of the sections, 

 in fact, have been wholly rewritten and illustrated from new and 

 original sources ; this may be seen in the sections on the History 

 as well as the Construction and Use of the Microscope and its appli- 

 ances, as also in those on Diatomaceae, Desmids, Saprophytes, 

 Bacteria, Rotifera, Acarina, and in the chapters on Microscopic 

 Geology and Mineralogy. To the same end nineteen new plates 

 have been prepared and 300 additional woodcuts, many of which 

 are also new, and for the use of the majority of those which are 

 not so, I am indebted to the Editors and Secretary of the Royal 

 Microscopical Society. 



There certainly never was a time when the Microscope was so 

 generally used as it now is. With many, as already stated, it is simply 

 an instrument employed for elegant and instructive relaxation and 

 amusement. For this there can be nothing but commendation, but it is 



