X PREFACE 



periodic changes of the age cycle in the organic indi- 

 \ddual as one aspect of the life-cycle. The present book 

 deals primarily with the problem of the nature of the 

 unity and order in the organism, the constancy of char- 

 acter and course of development, the maintenance of 

 individuality in a changing environment, and the 

 processes of physiological isolation, disintegration, and 

 integration or individuation in reproduction. The two 

 books, concerned as they are v/ith these intimately 

 associated aspects of the life cycle, are in many respects 

 complementary and together constitute a presentation of 

 the more important results and conclusions from the 

 writer's investigations and a consideration of certain 

 biological problems from the point of view attained. 



For permission to reproduce or to make drawings 

 based upon figures which have appeared in other books 

 acknowledgments are due to publishers as follows: to 

 the University of Chicago Press, for Figs. i6, 17, 25-27, 

 47, 48 in part, reproduced from Senescence and Reju- 

 venescence; to Wilhelm Englemann, for Fig. 13, drawn 

 after von Graff's Fig. 8, Tafel XVIII, in Monographic 

 der Turbellarien, I, Rhabdocoelida ; to Henry Holt & Co., 

 for Figs. 14 and 15, reproduced from Lillie, Development 

 of the Chick; to Gustav Fischer, for Fig. 86, reproduced 

 from Hildebrand, Die Gattung Cyclamen; to B. G. 

 Teubner, for Fig. 92, drawn after Fig. 84 in Goebel, 

 Einleitung in die experimentelle Morphologic der Pflanzen. 

 For certain figures drawn from botanical preparations 

 and for other figures not original, acknowledgments are 

 made in the legends. The writer is also deeply indebted 

 to Dr. C. J. Herrick and to Dr. W. J. G. Land, both of 

 the University of Chicago, for reading the manuscript 

 and for suggestions and criticisms. 



C. M. Child 



October, 19 15 



