x PREFACE 



and for permission to use unpublished data, and to 

 Dr. A. W. Bellamy of the Department of Zoology for 

 permission to use unpublished data and to reproduce 

 certain figures. 



For permission to reproduce published figures, 

 acknowledgments are due further to the following pub- 

 lishers and authors: D. Appleton and Co.; Henry Holt 

 and Co.; P. Blakiston's Son and Co.; The University 

 of Chicago Press; Professor S. Ramon Cajal; Dr. F. R. 

 Lillie; Dr. R. G. Harrison; Dr. W. A. Locy; Dr. J. B. 

 Johnston; Dr. G. H.Parker; and Dr. Charles Hill. The 

 sources of all figures reproduced are given in the legends. 

 To the artist of the Department of Zoology, Mr. Kenji 

 Toda, my thanks are due for his beautiful redrawing of 



figures reproduced. 



C. M. CHILD 



CHICAGO, ILL. 

 June, 1920 



