Studies on Regulation. 527 



seventeen days after section; Figs. 31 and 35, thirty-two days after 

 section. These two pieces belong to series which were begun on 

 the same day and examined at the same intervals as Series 71, 

 described in the preceding section. Figs. 28 and 32 may then be 

 compared with Fig. 15; Figs. 29 and 33 with Figs. 16, 20 and 24; 

 Figs. 30 and 34 with Figs. 17, 21 and 25; and Figs. 31 and 35 

 with Figs. 18, 22 and 26. This comparison shows that the 

 regeneration in these two pieces is less than in Series 71, a result 

 in accordance with the general statement made above since the 

 level from which regeneration occurs is somewhat further pos- 

 terior in these pieces than in Series 71. 



Other series from this level do not differ essentially from these 

 cases. 



The anterior regeneration after section near the middle of the 

 pharyngeal region is indicated in Figs. 36-39. Figs. 36 and 37 

 represent one extreme in which the wound remains open, and 

 Figs. 38 and 39 the other in which the contraction is so great that 

 the margins of the cut surface come into contact. Figs. 36 and 

 38 represent stages six days after section and Figs. 37 and 39 

 stages a month after section; Figs. 37 and 39 may be compared 

 with Figs. 31 and 35, and Figs. 18, 22 and 26. The amount of 

 regeneration is small when the edges come into contact as in Fig. 

 38. The two surfaces simply unite and no further growth occurs. 

 This contact of the cut edges is very common in the pharyngeal 

 region and probably results from the gradual retraction of the 

 cut end of the pharynx. In consequence of this the lateral parts 

 of the wound are brought into contact, since in the absence of the 

 pharynx the cavity in the median region collapses. The con- 

 dition with the edges of the cut surface in contact or nearly so is 

 more common in the pharyngeal region than that represented in 

 Figs. 36 and 37. 



Anterior regeneration from levels posterior to the pharynx is 

 very slight. In pieces from this part of the body the cut surface 

 does not usually close as it does in pieces from the pharyngeal 

 region since here there is no large median cavity. Fig. 40 shows 

 the condition thirteen days after section of a piece which repre- 

 sents the whole of the post-pharyngeal region (Fig. 27) and indi- 



