Studies on Regulation. 261 



weeks without food. At the stage shown in Fig. 6 (seventy-five 

 days) the specimen was much less active than at the stage of Fig. 

 3. Its movements were slow and it did not adhere very closely 

 to the substratum. The relative decrease in length of the old part 

 is probably simply the result of the decrease in longitudinal ten- 

 sion accompanying decrease in motor activity. The new^ part 

 does not show this change to such an extent since it is still in- 

 creasing in amount, /. e., relatively, at the expense of the old tissue, 

 as is evident from the Figs. 3-6 and from the measurements of 

 these stages in the table. 



The piece died about eighty days after section. 



Series 57 {Figs. J-ld). In this case section occurred near the 

 middle of the body, 9 mm. from the anterior end. In consequence 

 of contraction of the animal during section the cut was oblique on 

 the left side (Fig. 8), but this does not affect the value of the 

 results. 



This piece included portions of the region where the margins 

 are used for attachment, and so was able to hold to the substratum 

 and creep in the normal manner after section and before the regen- 

 erating part became functional, /. e., the regenerating posterior 

 end was not the only posterior organ of attachment, as in the pre- 

 ceding series. The small protruding piece on the left side was 

 much used for attachment even after the new tissue appeared. 

 In consequence of the ability of the piece to attach itself by the 

 margins and also because of the greater length of the piece the 

 change in direction of the tension is much less than in the pre- 

 ceding series. It might be expected therefore that the change in 

 form would be less rapid as well as less in amount than in the 

 preceding series. Figs. 9 (twenty-five days) and 10 (thirty-seven 

 days) represent later stages of the piece and it is evident that the 

 change of proportion is relatively slight. At the stages of Figs. 

 8 and 9 the width of the posterior region of the old tissue is rela- 

 tively less than at the time of section (see table) but in Fig. 10 the 

 proportions are almost the same as at the time of section. Exam- 

 ination of the figures and measurements will show that the width 

 at the posterior end underwent a relative decrease during earlier 

 stages, while in later stages a relative increase appears. In other 

 words the piece first acquired a somewhat tapering form without 

 much reduction in length but later reduction in length brought 

 about a return to approximately the originaF proportions. 



