iv PREFACE 



tion F (Zoology) of the American Association for the Advance- 

 ment of Science, together with the officers of the Association of 

 Southeastern Biologists, asked for suggestions on topics for a sym- 

 posium at the 1955 meeting of the AAAS in Atlanta. These two 

 organizations therefore decided to sponsor a symposium on the 

 species problem and invited me to serve as chairman. The Asso- 

 ciation's Section G (Botany), the American Society of Parasitolo- 

 gists, and the Society of Systematic Zoology agreed to cosponsor 

 the symposium. The strong backing of the symposium by these 

 organizations greatly contributed to its success. 



When selecting participants in the symposium one of my con- 

 siderations was to avoid duplication of similar earlier symposia. 

 Verne Grant, John Imbrie, and Hampton L. Carson, who had not 

 recently spoken on the species problem, were invited to discuss 

 the species problem in plants, in paleontology, and in genetics. 

 Their fresh approach was supplemented by treatment of groups 

 of organisms or topics that had not before been related to the 

 species problem: John Langdon Brooks agreed to speak on fresh- 

 water organisms, T. M. Sonneborn on protozoans, C. Ladd Prosser 

 on the physiological aspects of the species problem, and John A. 

 Moore on the species problem as seen by an embryologist. 



The papers are published essentially as given at Atlanta, with 

 one exception. Dr. Sonneborn, when preparing his contribution, 

 realized the need of a comprehensive survey of the species prob- 

 lem in the protozoans and particularly in the ciliates with their 

 interesting and versatile modes of reproduction. He found thai 

 the nature of their population structure, whether they are in- 

 breeders or outbreeders, is responsible for the specific aspects of 

 much of their reproductive specialization. To gather the material 

 with which to substantiate this new interpretation necessitated a 

 review of the widely scattered literature and could not be brought 

 to completion until well after the Atlanta meeting. Dr. Sonne- 

 born's masterly synthesis, a fundamental contribution to the pro- 

 tozoan literature, was not available for the chairman's summation. 



It would be too much to expect this symposium to solve the 

 species problem, yet it made a solid contribution toward its solu- 



