PHYSIOLOGY OF REGENERATION IN TUBULARIA. 1 59 



The simultaneous development of oral and basal polyps that 

 sometimes takes place indicates that there need be no absolute 

 antagonism between the development of polyps at opposite 

 ends, but only that such an influence tends to inhibit the begin- 

 ning stage of the polyp. It is also significant, I think, that the 

 basal development has a smaller retarding influence on the oral de- 

 velopment than vice versa, as the experiments show. This means 

 apparently that the locally stimulating factors have a stronger in- 

 fluence on an oral end, due possibly to the direction of the grada- 

 tion in the pieces. Other experiments show that this direction 

 is a factor in determining the rate. It may seem that this view 

 could be tested by a comparison of pieces of different lengths, for 

 a greater influence would be anticipated in shorter pieces, but it 

 is difficult to make such a test since the decrease in the rate of 

 response when the cut lies nearer the base seriously interferes 

 with a fair comparison being made. 



The Factors Involved in the Closure of the Open, 

 Cut Ends. 



The extremely rapid closure of the cut end of a stem by means 

 of a plate of cells that advances diaphragm-like from the cut 

 edge, has always excited my interest, because it throws a good 

 deal of light on the way in which movements of materials may 

 take place without any proliferation of new material entering into 

 the process. 



Renewed study has shown that the oral and the basal ends of 

 pieces close at the same rate ; that the edges of oral, cut surfaces 

 from the distal region of the stems close approximately at the 

 same rate as oral surfaces near the basal regions ; that the time 

 •of complete closure depends on the size of the piece, smaller 

 pieces closing sooner, since the rate of advance of the edge is 

 about the same in all ; and that the addition of salts and of 

 sugars to the sea water, if not so great in amount as to involve 

 serious changes, affect very little the rate of closure. Surface 

 tension therefore seems inadequate to explain the results, although 

 surface tension may play a minor role as a part of the stimulus 

 to contraction. 



Sections and surface mounts of different stages in the process of 



