PREFACE TO THE THIRD EDITION 



This edition conforms in the main to the preceding one, although 

 it has been fully revised in the light of the authors' experience in the 

 University of Missouri and that of teachers in other institutions 

 whose suggestions have been incorporated. Among other additions is 

 an extension of the work in vertebrate embryology and one outlining 

 such experiments in the genetics of Drosophila as we think feasible 

 for an introductory course. The list of figures suitable for laboratory 

 reference has been substantially extended, since we have found that 

 such figures, available at the convenience of the student, are much 

 more useful than the chart figures commonly used for a similar pur- 

 pose in most laboratories. As in the earlier editions the work out- 

 lined is designed to accompany the authors' "Textbook of General 

 Zoology," the third edition of which has recently appeared. 



We are again indebted to colleagues in the department of Zoology 

 at the University of Missouri and others for valued suggestions. 



University of Missouri 



Columbia, Missouri 



April 1, 1939 



