FOREWORD 



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

 embryology suitable for the intelligent layman and 

 the elementary students I have been conscious of 

 two main difficulties in this task. Firstly, embryos 

 are complicated and unfamiliar things, so that one 

 has to describe their structure before one can 

 discuss the problems they present. I have attempted 

 to avoid too much description by concentrating on 

 the early stages of development, which are as a 

 matter of fact the most important 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 

 views, perhaps without sufficient warning that they 

 represent probabilities rather than certainties. If I 

 had attempted to give all the possible interpretations 

 of the facts the book would have become unwieldy 

 and confusing, but it was impossible to shirk a 

 discussion of the problems. I believe the ideas which 



