PEEFACE 



TO THE SECOND EDITION. 



The highly favorable and quite unexpected reception 

 accorded the first edition of this book has stimulated my 

 interest in the subject, and in preparing a second, I have 

 sought to improve it as much as possible. In doing so, 

 many of the original sources of my information have 

 been re-examined, and from them some additions made 

 and inaccuracies corrected. The section on the Present 

 State of the Cell Dootritie, incorporating my own views, 

 has been entirely rewritten, as was necessitated by the 

 very important and numerous contributions to the subject 

 since the first edition appeared. 



The bibliography has been increased by the addition 

 of over three hundred and fifty new references, mostly 

 to papers contributed directly on the subject since the 

 first edition was issued. To make room for these, many 

 of the references included in the bibliography of the 

 first edition have been omitted where there did not seem 

 to be a sufficiently close bearing on the subject. 



