AtTHOR'S ABSTRACT OF THIS PAPER ISSOED 

 BY THE BIBLIOGRAPHIC SERVICE, MAT 23 



STUDIES ON THE DYNAMICS OF MORPHOGENESIS 



AND INHERITANCE IN EXPERIMENTAL 



REPRODUCTION 



XI. PHYSIOLOGICAL FACTORS IN THE DEVELOPMENT OF THE 

 PLANARIAN HEAD 



C. M. CHILD 



Hull Zoological Laboratory of the University of Chicago 



THIRTY-THREE FIGURES 



Earlier papers of this series and several other papers have 

 dealt with various aspects of the reconstitutional development 

 of Planaria dorotocephala in relation to experimental and 

 physiological conditions. It has been shown that development 

 may be altered and controlled within very wide limits (Child, 

 '09, '10 a, b, '11a, b, c, '14 b, '16 a, '20 a) and that widely 

 different developmental results, ranging from normal develop- 

 ment to complete absence of certain organs or organ complexes 

 and including different localizations and proportions of parts and 

 organs, may be determined and controlled by physiological 

 changes determined in a quantitative, rather than a specific way 

 (Behre, '18, Child, '11 a, '14 b, '16, '20 a). The head has proved 

 be of particular interest in these experiments, because of the 

 possibility of experimental control and modification of the 

 development of this most highly specialized region of the body 

 with the production of a graded series of head-forms ranging 

 from the normal to complete absence. 



Experiments of various investigators have shown that very 

 small pieces of the planarian body may give rise to heads alone. 

 These facts demonstrate that the head is able to develop in the 

 complete absence of other parts. This is true not only for 

 Planaria, but for other relatively simple organisms in which re- 



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THE JOURNAJ, OF EXPERIMENTAL ZOOLOGY, VOL. 33, NO. 2 



