FOREWORD 



views, perhaps without sufficient warning that they 

 represent probabilities rather than certainties. If 

 I had attempted to give all the possible interpre- 

 tations 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 I have put forward are those most 

 generally held by people who are working at em- 

 bryology at the present day, but tomorrow we may 

 discover some new fact which will force us to 

 modify them. When one is brought face to face 

 with the most fundamental questions about living 

 things, one cannot expect to obtain complete an- 

 swers in the comparatively short time during 

 which biology has been actively studied. 



C. H. W. 



