FOREWORD 



In this book, I have tried to write an account of 

 embryology suitable for the intelligent layman 

 and the elementary student. I have been conscious 

 of two main difficulties in this task. Firstly, em- 

 bryos are complicated and unfamiliar things, so 

 that one has to describe the problems they present. 

 I have attempted to avoid too much description 

 by concentrating on the early stages of develop- 

 ment, which are as a matter of fact the most im- 

 portant from a general theoretical point of view, 

 and can be described fairly shortly, since the 

 embryos have not yet had time to develop any 

 great complexity of form. The second difficulty 

 arises because embryology is so interesting. The 

 development of the structures by which living 

 things carry out the activities of life must clearly 

 raise many of the most fundamental problems 

 about the nature of life itself. But most of the 

 answers to these problems are still obscure. In 

 order to show the directions in which people's 

 thoughts are being led by the recent progress of 

 embryology, I have put forward some of my own 



