iv PREFACE 



Several authors and publishers have very kindly permitted 

 the use of illustrations or cliches from their works. Especial 

 acknowledgement is made to Professor F. R. Lillie for permis- 

 sion to use a considerable number of the illustrations in his 

 "Development of the Chick" (Henry Holt and Co.). I am 

 also indebted to Professor C. S. Minot and P. Blakiston's Son 

 and Co., for several cliches from their " Laboratory Text-book 

 of Embryology"; to Professor J. Playfair McMurrich and P. 

 Blakiston's Son and Co., for cliches from their "Development 

 of the Human Body"; to Messrs. Longmans Green and Co., 

 for cliches from "Quain's Anatomy"; to Messrs. G. P. Putnam 

 and Co., for permission to redraw, with some modifications in 

 most instances, certain illustrations in Marshall's " Vertebrate 

 Embryology"; to Professor T. H. Morgan and The Macmillan 

 Company, for cliches from their Development" of the Frog's 

 Egg"; and to Herr Gustav Fischer and the respective authors, 

 for cliches from 0. Hertwig's "Handbuch der vergleichenden 

 und experimentellen Entwickelungslehre der Wirbeltiere" ; 0. 

 Hertwig's "Lehrbuch der Entwickelungsgeschichte des Men- 

 schen und der Wirbeltiere"; and H. E. Ziegler's " Lehrbuch 

 der vergleichenden Entwickelungsgeschichte der niederen 

 Wirbeltiere." In all cases the cuts thus borrowed are separately 

 acknowledged in the figure legends. I desire also to express 

 my debt to the authorities of the Johns Hopkins University, 

 for library facilities generously afforded. 



W. E. K. 



July, 1913. 



