STUDIES ON THE PHYSIOLOGY OF RECONSTITU- 

 TION IN PLAN ARIA LATA, WITH A DESCRIP- 

 TION OF THE SPECIES. 



P. B. SIVICKIS, 

 Hull Zoological Laboratory, University of Chicago. 



The' earlier work on the reconstitution of isolated pieces of 

 planarians into new individuals was very largely concerned with 

 the description of the visible changes, such as the outgrowth of 

 new tissue, its differentiation, the reorganization and redifferenti- 

 ation of the old parts, the changes in shape, the minimum size of 

 pieces capable of reconstitution, and the relations between the 

 polarity of the new individual and that of the animal from which 

 the piece was taken. Most of the experiments were performed 

 with small numbers of pieces, often from different regions of the 

 body and without any attempt at a physiological standardization of 

 the experimental material. During the past twenty years Planaria 

 dorotocephala has been extensively used in this laboratory as mate- 

 rial for experimental investigation, and in the course of this work 

 various methods have been developed which have made possible 

 some degree of physiological analysis of the process of reconstitu- 

 tion in this species. In this work physiological standardization of 

 material, mass experiments, and control of environmental condi- 

 tions have played an important part. 



The desirability of including other species within the program 

 of investigation has become increasingly evident with the progress 

 of the work on P. dorotocephala, and at the suggestion of Dr. 

 C. M. Child the analysis of reconstitution in a closely related 

 species was begun. The present paper comprises a part of the 

 results of this investigation. 



In this connection I take the opportunity to acknowledge my 

 deep indebtedness to Professor Child for his advice, friendly criti- 

 cism, and revision of the manuscript. I also wish to express my 

 thanks to Dr. L. H. Hyman for the data on oxygen consumption 

 presented in this paper and for many helpful suggestions. 



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