DYNAMICS OF MORPHOGENESIS 123 



the pieces were placed in KCN all were examined and since the 

 high temperature made it probable that all would die in a few 

 days if left in the KCN, all that were then alive were returned to 

 water. The condition of the pieces at the end of the ten days in 

 KCN was as follows: 



Nine ^a-pieces were alive and were all of the type shown in 

 figure 26. Normal heads were present in all, but tail-formation 

 was completely inhibited : the new tissue merely closed the wound 

 and did not even fill the concavity of the contracted cut surface. 

 The anterior half of the old pharynx, which the piece contained 

 from the beginning, was much reduced and showed no signs of 

 regeneration. 



Of the 1 6-pieces seventeen were still alive : of these fifteen were 

 like figure 27 and two like figure 28. None of them showed any 

 trace of pharynx-formation. 



The condition of the shorter pieces, 2a, 2b, 2c after ten days in 

 KCN is shown, in figures 29 to 31. Th"e ^a-pieces, of which twenty- 

 one wer^^^live, were all much alike (fig. 29). An outgrowth of 

 new tissue had appeared at the anterior end and eyes and auricles 

 were distinguishable by their unpigmented areas, but no pharynx 

 had formed and at the posterior end nothing beyond closure of 

 the wound had occurred. 



Of the 26-pieces seventeen were still alive, all similar to figure 

 30. The anterior new tissue in these pieces is less in amount than 

 in 2a, neither eyes nor auricles have appeared as yet, the anterior 

 half of the pharynx, which these pieces contain, shows no regener- 

 ation and regulation at the posterior end is limited to wound- 

 closure. 



Seventeen of the ^c-pieces were alive: the anterior outgrowth 

 was less than in 2b and neither pharynx nor posterior end had 

 developed. Figure 31 shows the character of these pieces. 



The comparison of these five sets is of interest. In every piece 

 the regulatory processes at the posterior end are more completely 

 inhibited than those at the anterior end, moreover, the degree to 

 which the formation of the head is affected by the KCN varies 

 with the level of the pieces in the original body. Head-formation 

 is affected less in the 7a-pieces (fig. 26) than in the more posterior 



