PREFACE vii 



search for under " malaria," for instance, another would seek 

 under " mosquitoes," and vice versa. For this reason frequent 

 cross-references are given. 



As far as has seemed advisable, without too greatly encumber- 

 ing the text with round-about phrases, scientific terms have been 

 omitted or if used have been explained. It is difficult to keep 

 constantly before one the unfamiliarity with even everyday 

 scientific terms of many readers for whom this book is intended, 

 but an earnest attempt to do so has been made. 



In the text the author has purposely refrained from citing 

 references and from mentioning more than a few names of in- 

 vestigators. It obviously would be im|X)ssible to give refer- 

 ences, or even to mention more than a small per cent of the thou- 

 sands of contributors to the material here assembled without 

 making the text cumbersome and unreadable, especially for the 

 readers for whom the book is especially prepared. Only a few 

 of the leading figures in the history of each group of parasites 

 have been mentioned; other citations would have meant a 

 more or less arbitrary selection of a few from among many, 

 which must inevitably result in injustice. 



For similar reasons no bibliography is given. Instead, the 

 author has prepared a list of " Sources of Information " which 

 includes the names of all the leading periodicals in which im- 

 portant articles on parasitology have appeared or are likely to 

 appear, and a list of books which cover all or a portion of the field 

 of parasitology in a comprehensive manner. In these books 

 will be found bibliographies; most of the references cited in 

 these bibliographies will be found in the magazines or papers 

 listed in " Sources of Information " and this list will aid any- 

 one interested in pursuing the subject farther to keep in touch 

 with the new work which is constant^ appearing. The author 

 has felt that more real value would attach to such a list than to 

 a list perhaps 50 times as long and yet inevitably incomplete, 

 containing exact references to particular articles. 



The illustrations, with two or three exceptions, have been 

 drawn by the author either from specimens or from illustrations 

 of other authors. Pen and ink drawings have been used con- 

 sistently in place of photographs since it is believed that such 

 drawings, if carefully done, are far more valuable for scientific 

 purposes than are photographs. The trained eye is able by 



