Experiments on Polarity in Tiibidaria. 561 



tory to the formation of the new hydranth, are initiated by the 

 breaking down of the endodermal ridges near the oral end of the 

 piece. The cells of the ridges break up, setting free their contents 

 in the fluid. Since these cells contain red pigment, as well as 

 other products, the fluid becomes more or less filled with these 

 granules, as well as with broken cells or even entire cells contain- 

 ing the pigment. There is nothing mysterious or obscure in 

 regard to the source of this pigment in the fluid. It owes its 

 origin to the degenerative changes preparatory to forming a 

 hydranth. The ridges at the aboral end of the piece are also to 

 some extent absorbed, but much less so than at the oral end, ex- 

 cept in cases where an aboral hydranth is forming, when the same 

 extensive process of absorption occurs as at the oral end. It is 

 evident that the pigment observed in the circulation is a by-pro- 

 duct in the regeneration of the new hydranth, and from its origin 

 we get no suggestion of its being a substance formed for building 

 up a new structure. It will also be observed that the position of 

 the new hydranth, indicated by the degeneration of the endoder- 

 mal ridges, is already determined when the red pigment appears 

 in the circulation. 



Second. As has already been stated, the pigment, along with 

 other debris from the circulating fluid, is often collected in a ball 

 within the forming hydranth. It appears that at this time, when 

 the primordium of the hydranth is already laid down, the soluble 

 parts of the broken down cells in the circulation are absorbed, 

 presumably being digested, while the red pigment is not absorbed 

 but is later ejected from the mouth of the new hydranth. Whether 

 some part of it may not be absorbed as Loeb intimates, without 

 however showing that the process occurs, we cannot of course 

 state positively, but if this does happen, the amount absorbed 

 must be inconsiderable since the entire amount appears to be 

 ejected. Even if some of it were absorbed, — of which there is 

 no evidence, — ^it would be far too small in amount to account for 

 the pigment in the new hydranth. Loeb states that "the regen- 

 eration of a new polyp proceeds from those points where the 

 pigment granules collect." Our observations show that the pig- 

 ment granules more often collect at the distal end of the piece 



