2 68 RE GENERA TION 



the hydranth than elsewhere. If a piece of the stem is cut off, it 

 closes its cut-ends, and a circulation of fluid begins in the central cavity. 

 In this fluid globules now appear that contain the red-pigment granules. 

 The globules appear to be free endodermal cells, or parts of such, that 

 have been set free in the central cavity. In the course of twenty-four 

 hours the new hydranth begins to appear near one end of the stem, 

 and in this region of the stem a much larger number of granules ap- 

 pear. A little later all the red granules disappear from the circulation. 



Driesch has supposed that the red granules of the circulation be- 

 come a part of the wall of the new hydranth. The disappearance of 

 the red granules at this time from the circulation would seem to give 

 color to this view. But, on the other hand, I have found evidence 

 showing that this interpretation is incorrect. In the first place, the 

 granules that disappear from the circulation can be found lying in a 

 ball within the digestive tract of the newly formed hydranth ; hence 

 their disappearance can be accounted for, and we find that they are 

 not, or at least in large part are not, absorbed into the forming hy- 

 dranth. 1 In the second place, there is a great increase in the number 

 of endodermal cells in the region in which the hydranth is about to 

 appear, and the thickening that results takes place some time before 

 the granules begin to disappear from the circulation. The new gran- 

 ules appear in the new endodermal cells, and are presumably formed 

 by them. Again, the hydranth, that develops later at the distal end, 

 appears when there are no granules in the circulating fluid, and yet 

 the hydranth may contain as much red pigment as does the proximal 

 one. Lastly, the development of very short pieces shows that at the 

 time of the formation of the new hydranth there is an enormous in- 

 crease in the number of red granules in the piece, for there are many 

 more of them contained in the new hydranth than were present in the 

 entire piece at the time of its removal. 



Loeb has not referred to the red granules in the circulating fluid, 

 but simply to the red pigment which is present in the walls of the 

 piece. This is supposed to move forward into the hydranth region, 

 and call forth the development of a new hydranth. A study of the 

 number of the granules in the stem gives no support to this idea, 

 and the method of formation of single and of double hydranths in 

 short pieces shows that the increase in the number of granules in 

 the hydranth-forming region is not due to migration, but to local 

 formation. 



That specific substances may have an influence on the growth of 

 certain parts cannot be denied, but it appears that in general they 

 play a very secondary r61e as compared with other factors that 



1 Stevens ('01) has found that this ball of red pigment is ejected from the mouth of the 

 new hydranth. 



