DYNAMICS OF MORPHOGENESIS 437 



in the posterior direction (Child '13 c). In the one-fourth pieces 

 of table 2 this gradient continues to exist after section, the rate of 

 the second fourth being lower than that of the first. In some 

 other series the rates of first and second fourths immediately 

 after section are about the same, that is, the original gradient has 

 disappeared. In the one-sixth, one-eighth and one- twelfth 

 pieces (tables 5, 9 and 13) we see that in general the susceptibility 

 increases from piece to piece posteriorly, i. e., the original axial 

 gradient is reversed. This can be due only to the fact that more 

 posterior pieces are more strongly stimulated by section and 

 this is actually the case. A comparison of the susceptibilities 

 of Lot 1, which represents the most anterior fourth, sixth, eighth 

 or twelfth in tables 2, 5, 9 and 13, shows that the susceptibility 

 of this anterior region is but little affected by length of piece and 

 undergoes but little increase after section until we reach the one- 

 twelfth pieces, where the increase is greater than in the longer 

 pieces. The more posterior pieces are much more affected by 

 section and the tables show that in general the more posterior 

 the level of a piece the greater the degree of stimulation following 

 section. 



As regards the regional differences in rate immediately after 

 section, the results of the susceptibility method have been con- 

 firmed by estimations of CO2 production very kindly made at 

 my request by Dr. Tashiro with the apparatus devised by him 

 (Tashiro '13). In one-fourth pieces or larger the second piece 

 shows a lower rate of CO2 production than the anterior. In 

 one-sixth pieces the anterior piece has the lowest rate of CO2 

 production and the rate increases posteriorly from piece to piece. 



This regional difference in degree of stimulation agrees with 

 the wellknown fact of observation that when such animals as 

 earthworms and planarians are cut in two the posterior piece 

 usually reacts much more strongly than the anterior and it is 

 also in full accord with the theory of antero-posterior dominance 

 developed in preceding papers (Child 'lid, '13b, '13c), in fact 

 it constitutes valuable experimental evidence for this theory. 



The greater stimulation of posterior as compared with anterior 

 regions in consequence of section can only mean that the rate of 



