266 C. M. Child. 



mechanical factors since in the typical animal under typical con- 

 ditions those factors constitute a characteristic complex. 



But in all of the four cases described these changes are followed 

 in later stages of the experiment by changes in the reverse direc- 

 tion: the pieces become relatively shorter and broader until in 

 some cases the width of the body is relatively greater than before 

 section. These "inverse" changes in proportion carry the piece 

 farther and farther away from its original proportions. As was 

 noted above the motor activity of the pieces decreases in marked 

 degree long before death occurs and these changes are undoubtedly 

 the result of the decreased longitudinal tension consequent upon 

 the decrease in motor activity. As the tension decreases the eftect 

 of various internal physical conditions, capillarity, surface-tension, 

 etc., becomes manifest and it may be also that a reaction to the 

 altered conditions leads to reduction of the elongated parts, 

 though this reduction may be in part mechanical. 



The occurrence of these changes of proportion in opposite 

 directions disposes effectually of the idea that these pieces possess 

 some inherent capacity for assunnng the characteristic proportions 

 of the species. The piece will attain the characteristic propor- 

 tions at least approximately provided the characteristic complex 

 of conditions is present: changes in this complex result in changes 

 in proportion arwd changes in the reverse direction may occur under 

 certain conditions as I have shown. 



The changes in proportion are not as rapid nor as marked as in 

 Stenostoma or Planaria but they are similar in kind. The tissues 

 of Leptoplana are much firmer than those of the other forms men- 

 tioned and are consequently less readily affected by mechanical 

 conditions. Reverse changes in proportion have already been 

 described for Stenostoma (Child, '02) and I have also found them 

 in Planaria and other species. 



These four series of experiments on Leptoplana are sufficient 

 to illustrate the character of the changes in pieces containing the 

 cephalic ganglia. All other experiments of the same kind — some 

 twenty series — afforded similar results. The validity of the results 

 can scarcely be questioned since those of each series are in a sense 

 independent of the others. The measurements ol the various 

 stages and specimens were not tabulated and compared until long 

 after the experiments were concluded; thus the results obtained in 

 a given series were not influenced by the results of other experi- 



