Studies on Regulation. 265 



decrease in length. Fig. 16 represents the specimen ninety-six 

 days after section. A few days later it died. 



Series jg {Figs. ly-z^). The level of section in this series was 

 some distance posterior to the posterior end of the pharynx 

 (Fig. 17). Figs. 18-23 show the changes in form during one 

 hundred and thirty-six davs. The changes in form of the old 

 part are relatively slight in this case as might be expected since 

 only the posterior end is removed and the changes in the direction 

 of tension are only slight. But a relative reduction in the width 

 ot the body in the posterior part ot the old tissue does occur during 

 the first sixty-one days of the experiment as the figures and the 

 table show, /. <?., during this time the old part has become rela- 

 tively longer and more tapering. 



As the activity of the piece decreases during the later part of the 

 experiment, however, a change in the reverse direction occurs; 

 the piece becomes relatively shorter and broader until at the last 

 stage measured (Fig. 23, 136 days after section) the posterior 

 width of the old part is slightly greater in proportion to the length 

 than it was at the time of section. 



Circumstances made it necessarv^ to conclude the experiment 

 at the stage of Fig. 23, but there is no doubt that further relative 

 decrease in length would have occurred had the piece been kept. 



2. Discussion of the Experiments. 



In all the four series of experiments described the results are 

 similar; in each piece the old part becomes relatively longer and 

 more slender during the earlier part of the experiment. The 

 greatest change in all cases is in the width at the posterior end of 

 the old part which undergoes greater reduction than the width at 

 the anterior end, i. e., the body assumes a more tapering form. 

 These changes in proportion differ in degree according to the level 

 at which section is made, being in general greatest in short pieces. 

 As I have shown tor Stenostoma (Child, '02) this is exactly what 

 must be expected if the changes in form are the result of the 

 changes in tension connected with locomotion. It is evident that 

 it these changes in proportion continued the piece would finally 

 attain proportions approximating those of the specimen from 

 which it originated, ;. c, the characteristic proportions of the 

 species. This also is to be expected il these changes are due to 



