PREFACE IX 



whose skill in microtechnique has been of great benefit in my re- 

 search. She has given much practical help in connexion with the 

 experiments described in the Appendix. Mrs J. A. Spokes has 

 helped me with this book more than anyone else, by acting as my 

 secretary with uniform accuracy and good nature. Several of the 

 illustrations have been copied photographically from old books and 

 journals. ]\Ir P. L. Small and Mr J. S. Haywood have taken a lot 

 of trouble to produce as good copies as possible. Dr W. G. B. 

 Casselman has most kindly made several readings of the oxidation- 

 potentials of fixatives specially for this book. 



I take the opportunity of mentioning the benefit I have derived 

 during the last eleven years from my association with Dr C. F. A. 

 Pantin, F.R.S., in joint editorship of the Quarterly Jour?ial of 

 Microscopical Science. 



John R. Baker 

 Cytological Laboratory, 



Department of Zoology, 

 University Museum, 

 Oxford. 



