Studies on Regulation. 267 



ments. This fact renders the agreement between the different 

 series all the more convincing. Moreover, the experiments show, 

 I think, that it is not impossible to obtain fairly accurate series of 

 measurements, even of animals so changeable m form as these. 



These four series also afford some interesting data bearing upon 

 the questions discussed in my second paper upon Leptoplana 

 (Child, '04b). As regards the amount of regeneration Series 27 

 (Figs. 1-6) and Series 57 (Figs. 7-10) are nearly equal but in 

 Series 58 (Figs. 11-16) the amount of regeneration is much less 

 and in Series 59 (Figs. 17-23) still less. As regards Series 27, 58 

 and 59 the result agrees with the conclusion reached regarding this 

 point in the paper above mentioned, viz: that the amount of pos- 

 terior regeneration is proportional to the size of the part removed. 

 According to this Series 58 might be expected to show less regen- 

 eration than Series 27 but as a matter of fact the amount of regen- 

 eration is greater than in any other piece among the hundreds 

 examined. This case is an individual exception but the only one 

 observed. At all events comparison of these pieces from different 

 series shows that the amount of regeneration is much less when the 

 level of section is in the posterior half than when it is in the anterior 

 half. The bearings of this fact were discussed in the paper 

 referred to above. 



The form of the regenerated part requires only brief considera- 

 tion. It is so manifestly determined in large degree by the me- 

 chanical conditions connected w^ith locomotion that discussion is 

 scarcely necessary. The decrease in width of the new part without 

 corresponding increase in length which is most evident in Series 

 27 (Figs. 3-5) can scarcely be accounted for except as the result 

 of longitudinal tension. 



The differences in the rapidity and amount of intestinal regen- 

 eration are also well illustrated by the four series. The rapidity 

 and amount of regeneration is greatest in Series 27 (Figs. 2-6), 

 slightly less in Series 57 (Figs. 8-10) much less in Series 58 (Figs. 

 12-16) and scarcely perceptible in Series 59 (Figs. 18-23). The 

 difference is not merely absolute and dependent upon the size of 

 the new part but is relative, the extent of the intestine in the new 

 tissue being relatively greatest in Series 27 and decreasing with 

 approach of the level of section to the posterior end. 



Moreover, in the later stages of Series 58 (Figs. 14-16) and 

 Series 59 (Figs. 21-23) the intestinal branches in the new tissue 



