viii PREFACE 



voluntary concentration on certain parts, and inattention to 

 others, to see much more than can a camera, which has no such 

 power of adjustment. A pen and ink drawing can, therefore, 

 represent more accurately what can be seen by the eye than can 

 a photograph. The author has received valuable advice re- 

 garding the illustrations from Mr. A. J. Stover, scientific il- 

 lustrator at the Oregon Agricultural College, and wishes to take 

 this opportunity to express appreciation for it. 



Deep appreciation is felt for the invariable willingness with 

 which authors, editors and publishers of scientific papers and 

 books have given permission to copy illustrations. Special 

 mention should be made, however, of the generosity of Sir 

 Patrick Manson and of the American publishers of his " Tropical 

 Diseases," Wm. Wood and Co.; of Dr. A. Alcock, author of 

 " Entomology for Medical Officers"; of Professor Wm. A. Riley 

 and Dr. Johannsen, authors of " A Manual of Medical Ento- 

 mology," and of Dr. A. W. Sellards, who, in the absence of Dr. 

 Strong, lent photographs taken in Peru by the Harvard School 

 of Tropical Medicine. The illustrations taken from the journal 

 Parasitology have been especially numerous, and mention should, 

 therefore, be made of the unreserved permission to use them 

 given by the editor, Professor G. H. F. Nuttall. Many illus- 

 trations of worms have been taken from the work of two of the 

 real pioneers in the study of helminthology, Professor Karl 

 Leuckart of the University of Leipzig, under whom many of 

 the present parasitologists were trained, and Professor Arthur 

 Looss of the University of Cairo in Egypt. It is a high tribute 

 to the work of Professor Leuckart that many illustrations 

 published by him in the first comprehensive work on the animal 

 parasites of man, in 1863, are still the best available ones and 

 will be found reproduced in the majority of modern works on 

 the subject. 



Particular appreciation is felt for the assistance received from 

 three publications which contain reviews of current literature 

 in particular phases of medical zoology, namely, the Tropical 

 Diseases Bulletin, which reviews practically all current work 

 on protozoan parasites and helminthology, the Review of Applied 

 Entomology, Series B, containing abstracts of nearly all work 

 on medical and veterinary entomology, and the Journal of the 

 American Medical Association, which gives references to all 



