VI PREFACE 



ity, in spite of a didactic presentation. Tlie objective presentation of 

 the truth, as far as it can be apprehended at the moment, is the 

 extent of one's responsibility. Accuracy should be the moral and 

 ethical responsibility of every author of a treatise on a scientific sub- 

 ject. To the best of the author's knowledge, the descriptive material 

 of this book is demonstrably accurate. 



The author, as a teacher, has found it increasingly important that 

 there be a common language by which information can be imparted 

 to the student. This necessity is met in part by a Glossary of embryo- 

 logical terms, readily accessible to the student and rigidly adhered to 

 by the instructor. For this reason, the book breaks with tradition to 

 include a complete Glossary of some 750 words. A definition will 

 often clarify or crystallize a complicated and detailed description. 

 Therefore it is hoped that the student will increase his functional 

 vocabulary to the extent of the appended Glossary. 



The author is also an enthusiastic advocate of the visual elucida- 

 tion of the oral description. Most illustrations are useful, some are 

 indispensable. Therefore a profusion of illustrations appears in this 

 book, most of which are original and based on direct observation of 

 the egg and embryo. In a few cases excellent illustrations of other 

 workers have been borrowed or slightly modified for inclusion in this 

 text. 



The seed for this book was planted early in the author's mind while 

 he was being initiated into the field of embryology by Professor Robert 

 S. McEwen of Oberlin College. During a long period of incubation 

 the plan slowly matured. Experience, gained over the years in teach- 

 ing and learning from the response of interested students, helped to 

 bring into clearer focus the aims to be sought for in this book as a 

 teaching text. The execution of the task and the finished form pre- 

 sented here could not have been attained at this time but for the in- 

 valuable assistance given by the publishers and their staff. Thanks 

 are due to Miss Marie Wilson and to The Blakiston Company — 

 especially to Mr. William B. McNett and Miss Gloria Green of the 

 Art Department who helped with the illustrations; to Mr. Willard 

 Shoener of the Production Department; and most particularly to Miss 

 Irene Claire Moore and Dr. James B. Lackey of the Editorial Staff. 

 Special acknowledgment is also given to the General Biological 

 Supply House of Chicago, whose illustration of the frog is used so 

 effectively on the title page. It remains for the professor and the 



