DYNAMICS OF MORPHOGENESIS 425 



more than that of the anterior. In table 8, one hundred and 

 twenty hours after section, this has occurred and the suscepti- 

 biUty of all three lots is almost the same. Still later the sus- 

 ceptibility of the posterior pieces provided they undergo complete 

 reconstitution, may become even greater than that of the anterior 

 pieces. 



4. The one-eighth pieces 



The regions represented by the pieces are shown in figure 3. 

 In tables 9 to 12 only the records of pieces 1 to 4 are given. 



Table 9 compared with tables 5, 2 and 1 shows that in the first 

 four one-eighth pieces the susceptibility is higher immediately 

 after section than in the one-sixth pieces or one-fourth pieces or 

 in the whole worms. Not only do these pieces complete disinte- 

 gration earlier than the others, but the first traces of disintegration 

 appear earlier. 



After twelve hours, however, as shown in table 10, the suscepti- 

 bility has decreased so that it is about the same as that of the 

 whole animals. At twenty-four hours and also at forty-eight 

 hours (table 11) it is still about the same. Seventy-two hours 

 after section the susceptibility is again higher, at ninety-six hours 

 still higher and at one hundred and twenty hours (table 12) it 

 is higher still. Many of these short pieces in the more posterior 

 regions do not undergo complete reconstitution but remain head- 

 less and in these the susceptibility does not undergo as great an 

 increase as in those which produce wholes. 



But the one-eighth like the one-sixth pieces show regional dif- 

 ferences in the increase in susceptibility iimnediately following 

 section. In table 9 it is evident that the anterior pieces (Lot 1) 

 are in general least susceptible, the second eighths (Lot 2) con- 

 siderably more susceptible, the third eighths (Lot 3) slightly more 

 susceptible than the second, and the fourth eighth (Lot 4) about 

 like the third. Here, as in the one-sixth pieces, the regions of the 

 body which in the uninjured animal have lower susceptibility 

 show a higher susceptibility after section, that is, the stimulation 

 resulting from section is least in the anterior piece and increases 



THE JOURXAL OF EXPERIMEN'TAL ZOOLOGY, VOL. Iti, NO. 3 



