vi PREFACE 



any such result, constitute in some degree an attempt at a comparative 

 consideration and analysis of data concerning some of the various sorts of 

 development and the characteristics of their patterns, with some discus- 

 sion of what is known or believed or remains to be discovered concerning 

 their origins. Embryonic development is considered not as the primary 

 and fundamental form of development to which all other patterns are to 

 be referred but rather as representing a relatively specialized type to be 

 interpreted in the light of what we learn concerning other more primitive 

 developmental patterns. 



In certain species buds (often more than one kind of buds), isolated 

 pieces of various sizes from various parts of the body, and even aggregates 

 of dissociated cells may all give rise to individuals of the same sort as the 

 individual developing from an egg. These different starting-points ob- 

 viously do not all have the same pattern or organization as the egg, but we 

 can scarcely avoid the conclusion that the essential factors of pattern 

 must be similar in all. What are these factors, as distinguished from those 

 incidental to a particular sort of development? To the writer this ques- 

 tion appears to present a fundamental problem of developmental physiol- 

 ogy. With it this book is largely concerned. 



Permission to reproduce copyrighted figures is gratefully acknowledged 

 as follows: to Verlag JuHus Springer, Berlin, to the Yale University 

 Press, and to Professor Spemann for Figure 156, A-H, a reproduction of 

 Figure i, a-h, from Spemann, Experimentelle Beitrage zu einer Theoric der 

 Entwicklung (1936; American ed.: Embryonic Development and Induction 

 [1938]) ; to Verlag Georg Thieme, Leipzig, for Figure 159, A-C, and Figure 

 160, reproductions of Figures 1-4 from Holtfreter, Biologisches Zentral- 

 hlatt (1933), Band 53, Hefte 7, 8; to the American Book Company for 

 Figure 206, B and C, after Figures 394 and 395 from Coulter, Barnes, and 

 Cowles, A Textbook of Botany (1910); to the University of Chicago Press 

 for Figure 208, A, after Figure 364 from Coulter and Chamberlain, 

 Morphology of Gymnos perms (1910); to D. Appleton-Century Company 

 for Figure 210, A-C, after Figures 600, 601, and 602 from Coulter and 

 Chamberlain, Morphology of Angiospcrms (1903); to Librairie-imprimerie 

 Gauthier-Villars, Paris, and to Professor Dalcq for Figure 219, A and B, 

 after Figure 23, a and b, from Dalcq, V organisation dc Va'uf chez les 

 C hordes (1935); to the Cambridge University Press and to Sir D'Arcy 

 Wentworth Thompson for Figures 222, 223, and 224, from Figures 369, 

 381, 382,404, 406, and 407 of Thompson, Grow//? aw^ Forw (1917). Special 

 acknowledgment is made with deep appreciation to Professor Dalcq for 



