PREFACE 



E three Lectures forming the first part of this book were 

 given as one of the "Advanced Courses in Zoology" in the 

 University of London. They were delivered at Guy's Hospital 

 on January 23rd, January 30th and February 6th, 1913, under 

 the title "The Growth in Length of the Vertebrate Embryo." 

 They are now published in accordance with the known intention 

 of the author, and in response to the expressed wish of some of those 

 who heard them. 



Although my husband had destined this work for publication, 

 he had not actually prepared it for the press ; but the Lectures 

 were typewritten and some corrections and notes had been added 

 to them. For help in arranging them for print I am greatly 

 indebted to Professor Stanley Gardiner, F.R.S., and to Professor 

 J. P. Hill, F.R.S., who have most kindly read the MSS; and to 

 the latter especially for valuable suggestions as to some altera- 

 tions in the original wording, which while adapted for lecturing 

 purposes might not always have been clear to the reader. 



The figures have been drawn by Miss D. Thursby-Pelham from 

 the sketches given in the MSS referring to lantern slides and 

 diagrams displayed during the lectures. 



The cost of publication is partly defrayed by a grant from the 

 Royal Society. 



The second part of the book consists of a reprint of a paper 

 on the Mechanics of Gastrulation which appeared in theArchivfur 

 EntwicJdungsmechanik der Organismen in 1910. It is here included 

 as the subject is kindred to that of the lectures and also because 

 it is often in demand and further copies are unobtainable. 



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