TABLE OF CONTENTS 



Introduction ........... 



PART I. THE PROBLEM OF ORGANIC CONSTITUTION 

 Chapter 



I. Various Theories of the Organism 



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 



Page 



I 



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 . g2 



The Experimental Material; Age Differences in Susceptibilty in Pla- 

 naria maculaia; Age Differences in Susceptibility in Planaria 

 dorotocephala; Age Differences in Susceptibility in Other Forms; 

 Conclusion; References. 



V. The Reconstitution of Isolated Pieces in Relation to Re- 

 juvenescence IN Planaria 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 Ani- 

 mals Resulting from Experimental Reproduction and Sexually 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 dorotocephala and Re- 

 lated Forms; The Occurrence of Rejuvenescence in Agamic Reproduc- 

 tion in Planaria dorotocephala and P. maculata; Agamic Reproduction 

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

 juvenescence in Stenostomum and Certain Annelids; The Relation be- 

 tween Agamic Reproduction and Rejuvenescence in Protozoa; Agamic 

 Reproduction and Rejuvenescence in Coelenterates; References. 



