x PREFACE 



they have been retained, and in view of the great importance 

 of the study of unicellular organisms at the present time, 

 an apology is scarcely needed for devoting a somewhat dis- 

 proportionate amount of space to them. My thanks are due 

 and are hereby tendered to Professor G. H. F. Nuttall and 

 Mr A. E. Shipley, Fellow of Christ's College, Cambridge, for 

 permission to copy their excellent figures of the female, larva, 

 and mouth parts of Anopheles maculipennis ; to Dr J. W. 

 Jenkinson of Exeter College, Oxford, for advice and assistance 

 in the chapter relating to Cytology, and to Mr C. Clifford Dobell, 

 Fellow of Trinity College, Cambridge, for much advice and 

 for permission to reproduce his figures illustrating the 

 structure and life-history of Copromonas subtilis. 



GILBERT C. BOURNE. 



SAVILR HOUSE, OXFORD, 

 May 1909. 



