TABLE OF CONTENTS 

 Introduction .......... 



PART I. THE PROBLEM OF ORGANIC CONSTITUTION 

 Chapter 



I. Various Theories of the Organism 



Pace 

 I 



Neo-vitalistic Theory; Corpuscular Theories; Chemical Theory; 

 Physico-chemical Theory; The Colloid Substratum of the Organism; 

 The Relation between Structure and Function; References. 



II. The Life Cycle 



34 



Growth and Reduction: Definitions of Growth and Reduction, The 

 Nature of Growth and Reduction; Differentiation and Dedifferentia- 

 tion: Differentiation, Dedifferentiation; The Basis of Senescence and 

 Rejuvenescence; References. 



PART II. AN EXPERIMENTAL STUDY OF PHYSIOLOGICAL SENES- 

 CENCE AND REJUVENESCENCE IN THE LOWER ANIMALS 



III. The Problem and Methods of Investigation .... 63 



The Nature of the Problem; Susceptibility in Relation to Rate of Metab- 

 olism; The Direct Method; The Indirect Method; Other Methods; 

 References. 



IV. Age Differences in Susceptibility in the Lower Animals . 92 



The E.xperimental Material; Age Differences in Susceptibilty in Pla- 

 naria maciilata; Age Differences in Susceptibility in Planar'ui 

 dorolocephala; Age Differences in Susceptibility in Other Forms; 

 Conclusion; References. 



V. The Reconstitution of Isolated Pieces in Rel.\tion to Re- 

 juvenescence IN Planar ia and Other Forms 103 



The Reconstitution of Pieces in Planaria; Changes in Susceptibility 

 during the Reconstitution of Pieces; The Increase in Susceptibility in 

 Relation to the Degree of Reconstitution; The Susceptibility of .\ni- 

 mals Resulting from E.xperimental Reproduction and Se.xually Pro- 

 duced Animals; Repeated Reconstitution; References. 



VI. The Relation between Agamic Reproduction and Reju- 

 venescence IN the Lower Animals 122 



The Process of Agamic Reproduction in Planaria dorolocephala and Re- 

 lated Forms; The Occurrence of Rejuvenescence in .\gamic Reproduc- 

 tion in Planaria dorolocephala and P. maculala; .-\gamic Reproduction 

 and Rejuvenescence in P. velala; Agamic Reproduction and Re- 

 juvenescence in Slenoslomum and Certain Annelids; The Relation be- 

 tween Agamic Reproduction and Rejuvenescence in Protozoa; .\gamic 

 Reproduction and Rejuvenescence in Coelenterates; References. 



ix 



