VI PREFACE 



any single author for any particular part of the work. 

 The following books, however, have been particularly 

 helpful: 



The Development of the Chick, Lillie. 



Embryology of the Chick and the Pig, Lillie. 



The Development of the Human 'Body, McMurrich. 



Text Book of Embryology, Hertwig-Mark. 



Elements of Embryology, Foster & Balfdur. 



Laboratory Text Book of Embryology, Minot. 



A Manual of Histology and Organography, Hill. 



Text Book of Zoology, Galloway. 



The Cell in Development and Inheritance, Wilson. 



The author wishes to express her gratitude to Dr. 

 R. K. Nabours for his criticism of a part of the manu- 

 script and to Dr. Paul S. Welch for reading and criticising 

 the entire manuscript. MARY T. HARMAN. 



