48 C. M. CHILD. 



that tentacles could not arise proximal to the two which have ap- 

 peared, because there the two sides of the cut united almost 

 directly. The two tentacles represent the last interseptal chamber 

 on each side which was opened by the incision. The next inter- 

 septal chambers lateral to these on each side are continuous to 

 the oral end of the body and the first of the normal tentacles on 

 each side above the cut corresponds to one of them. The reason 

 for the atrophy of the old tentacles above the cut is at once ap- 

 parent from the figure. In consequence of the approximation of 

 the sides of the cut and the contraction of the oblique slip the 

 interseptal chambers to which these tentacles belong have been 

 cut off from communication with the rest of the enteron. In the 

 living specimen this portion of the body was very evidently col- 

 lapsed, while other parts were distended. 



October II. — No marked changes since September 28. 



December ji. — During the period between October 1 1 and this 

 date the specimen was not examined closely since the formation 

 of tentacles in the lateral region was the chief purpose of the 

 experiment. On this date, when the experiment was concluded, 

 examination showed that the two small tentacles had disappeared, 

 the new tissue which closed the wound had become thicker and 

 more like the old body-w^all and extended over a larger area than 

 before, and finally the tentacles above the cut on the terminal 

 disc had once more grown out to the same length as the others. 

 At this time the marginal tentacles were 7-8 mm. in length and 

 the labials 1-2 mm. In the course of regulation the contracted 

 area resulting from the approximation of the margins of the cut 

 had again spread out in consequence of the growth of new tissue 

 and the interseptal chambers were again in communication with 

 the rest of the enteron, hence the tentacles corresponding to them, 

 which were previously atrophied, had developed to the same 

 length as the others. 



During a considerable part of this time the animal was in a 

 burrow which it had made for itself in the sand, and it is probable 

 that the pressure of the body-wall against the wall of the burrow 

 aided in bringing about the disappearance of the two tentacles. 



In this case, as in those discussed above, the special result is 

 determined by the conditions of the experiment. No new method 



