STUDIES ON REGULATION. 



VII. FURTHER EXPERIMENTS ON FORM-REGULATION IN 

 LEPTOPLANA. 



BY 



C. M. CHILD. 



With 34 Figures. 



The present paper is devoted to a consideration of certain 

 phases of the process of form-regulation in Leptoplana, which, 

 although of great interest when viewed in the light of the conclu- 

 sions reached in previous papers on Leptoplana (Child, '04a, 

 '04b, '04c), do not in themselves afford sufficient data for these 

 conclusions. Considered at this time they serve to confirm and 

 extend the conclusions already drawn from other data. 



A. TYPICAL CHANGES IN PROPORTION DURING REGULATION. 



During the process of form-regulation of pieces in many of the 

 lower animals certain changes of form occur which involve not 

 only the new parts but also the old fully differentiated regions. 

 Under normal conditions these changes consist in approximation 

 to the typical proportions of the species. A description of these 

 changes in Planaria, where they are considerable, has been given 

 by Morgan ('00) who has applied tb them the term "morphal- 

 laxis." I have shown recently (Child, '02, '03) that similar 

 changes in Stenostoma are at least in part the result of traction 

 upon the, parts in certain directions in consequence of the charac- 

 teristic motor activity and I have obtained strong evidence as yet 

 unpublished, that the same factors are concerned in Planaria. 

 But the term "morphallaxis" has been applied to phenomena 

 which, in rny opinion, are wholly diverse and therefore, although 

 I have employed it in c-^rtain previous papers (Child, '02, '03a, 

 '03b), it seems preferable to use some less vague term. Driesch 

 ('01) considers "morphallaxis" identical with his "Restitution 

 d|urch Umdifferenzierung," but morphallaxis may occur without 



