VIII PREFACE 



mon to many other teachers — never to give a course in exactly the same way 

 two years in succession. This procedure enlivens a course and keeps suc- 

 cessive groups of students out of the rut of looking forward to the same identical 

 lectures and laboratory approach year after year. As a result, in reality this 

 book is a compilation of the different aspects of embryology presented by the 

 author over a period of years to classes in comparative vertebrate embryology. 

 Consequently, by the use of certain chapters and the outlines at the headings 

 of each chapter, various facets of embryology may be presented one year 

 while other aspects are selected the following year, and so on. Moreover, a 

 selective procedure allows the book to be used readily for short courses in 

 embryology as well as longer courses. For example. Chaps. 3, 5-1 1 , and 20-22 

 may serve as the basis for a short course in vertebrate embryology. 



Another feature of the text is the presentation of many illustrations well 

 prepared. Illustrations are an important adjunct to the teaching of embryology. 

 This is true especially where the teacher is burdened with the teaching of other 

 courses and thus is handicapped by lack of time to make adequate blackboard 

 drawings and illustrations of laboratory and lecture material. In Chaps. 3, 

 5-1 1, and 20-22, one finds illustrative material adequate to enable the student 

 to gain an appreciation of the fundamental features of vertebrate development. 

 Thus, this part of the book may be used extensively as a laboratory guide to 

 the fundamental principles involved in vertebrate development. 



A final aspect of the text may be mentioned, namely, the references given 

 at the close of the chapters. References to literature are important especially 

 in courses of embryology where small groups of students are assembled. 

 Under these conditions the teacher often prefers to give the course on a 

 seminar basis. With this approach, references are most valuable in the assign- 

 ment of special reports and student lectures which the student later gives to 

 the class as a whole. 



