DYNAMICS OF MORPHOGENESIS 



423 



more susceptible than 1; in other words, the susceptibiUty of pos- 

 terior is greater than of anterior pieces. This change constitutes, 

 so far as the different pieces are concerned, a reversal of the 

 axial gradient of the first zooid of uninjured worms. It is a char- 

 acteristic feature not only of sixths but, as will appear below, 

 of all shorter pieces and is due to the fact that posterior pieces 

 are more stimulated by the act of section than anterior. 



After twelve hours (table 6) the effect of this stimulation has 

 disappeared in Lot 2 so that its susceptibility is lower than that 



TABLE 7 

 Susceptibility to KCN 0.001 m. of one-sixth pieces forty-eight hours after section. 



