viii PREFACE 



my research program for the last twelve years, during which time 

 work has been actively carried on with the aid of a number of gradu- 

 ate students, with facilities furnished by the University of Chicago, 

 the Marine Biological Laboratory, and, more recently, with financial 

 aid from a grant from the Rockefeller Foundation to aid investiga- 

 tions in the biological sciences at this university. The preparation of 

 the manuscript of this book has been, in part, supported by aid from 

 this latter source. 



In addition to the loyal co-operation of students and colleagues in 

 the accumulation of experimental data, of citations, and of criti- 

 cisms, aid with the scattered literature has come from friends and 

 acquaintances from five continents. The extended hterature hst is 

 incomplete, but the labor of gathering and selecting the references 

 used has been appreciably decreased by this cordial co-operation. 



Certain specific acknowledgments I have made in the text. I am 

 also indebted to Drs. Marie A Hinrichs, A. M. Holmquist, Walburga 

 A. Petersen, J. M. Shaver, and O. Park; to Messrs. M. R. Garner, 

 J. R. Fowler, J. F. Schuett, W. A. Dreyer, Carl Welty, W. H. John- 

 son, E. O. Deere, Ralph Buchsbaum, D. A. D. Boyer, J. F. W. Pear- 

 son, and T. Park; to Mrs. Frances Church van Pelt and Mrs. Gret- 

 chen Shaw Rudnick; and to Miss Edith Bowen, for citations to per- 

 tinent hterature, for permission to give results before pubhcation, or 

 for criticism of parts of the manuscript, or for all three; to Professor 

 F. R. Lillie, who read critically chapters xvi and xvii; to Professor 

 A. E. Emerson for similar service with chapters xix and xx; to Mr. K. 

 Toda, who drew or copied the text figures; and to Marjorie Hill 

 Allee for editorial assistance with the manuscript. Acknowledgment 

 of courtesy in permitting reproduction of figures will be given else- 

 where. 



W. C. Allee 



Whitman Laboratory or Experimental Zoology 

 University of Chicago 

 August, 1930 



