CONTENTS 



Species Concepts and Definitions 



Ernst Mayr 1 



The Species as a Field for Gene Recombination 



Hampton L. Carson 23 



The Plant Species in Theory and Practice 



Verne Grant 39 



The Species Problem in Freshwater Animals 



John Langdon Brooks 81 



The Species Problem with Fossil Animals 



John Imbrie 125 



Breeding Systems, Reproductive Methods, and Species 

 Problems in Protozoa 



T. M. Sonneborn 155 



An Embryologist's View of the Species Concept 



John A. Moore 325 



The Species Problem from the Viewpoint of a Physiologist 



C. Ladd Prosser 339 



Difficulties and Importance of the Biological Species 



Ernst Mayr 371 



Index 389 



73475 



IX 



