iv PREFACE 



indeed followed the general arrangement adopted by these 

 authors fairly closely except in one respect. I believe so 

 strongly that the processes of growth and cell-division, though 

 they always (in the Metazoa) accompany, are yet distinct 

 from, differentiation, that I have felt justified in treating them 

 in a chapter apart from the other internal factors of develop- 

 ment. The external factors whether of growth, cell- division, 

 or differentiation are discussed in Chapter III, and the 

 ground is thus cleared for a consideration of the real problem 

 the differentiation of specific form. 



The last chapter is devoted to the theories, scientific and 

 philosophical, of Hans Driesch. I sincerely hope that Herr 

 Driesch will allow my great admiration for the former to 

 atone in some measure for my inability to accept the tenets 

 of neo- vitalism. 



It is a very great pleasure to me to acknowledge my 

 indebtedness to the Delegates and Secretaries of the Clarendon 

 Press, and in particular to Professor Osier, for undertaking 

 the publication of this book, as well as for the pains which 

 have been expended in its preparation. Dr. Osier also took the 

 trouble to read through the whole of the manuscript, and 

 Mr. G. W. Smith and Dr. Haldane have been kind enough to 

 look through certain chapters. 



To Dr. Eamsden I am under great obligations for his 

 assistance in that part of Chapter II, Section 1, in which 

 surface-tensions are discussed ; to Dr. Vernon for calling 

 my attention to Roberts' s work on Anthropometry, and to 

 Mr. Grosveuor for the information embodied in the foot-note 

 on p. 89. Mr. A. D. Lindsay has given me invaluable 

 assistance in those sections of Chapter V which deal with 

 the philosophy of Kant, while, for Aristotle, I was fortunately 

 able to attend Professor Bywater's lectures on the De Anima. 



I can hardly express the debt I owe to Mr. J. A. Smith for 

 much friendly counsel and criticism, although he is, of course, 



