Grafting of Tiihularia 



347 



(Fio-. 19, C) so that the oral surfaces were exposed. A series of 

 twenty-four grafts is represented in Table 18. 



TABLE 18 



1 



Out of twenty-four grafts, twelve developed a hydranth first 

 on one end, then on the other in spite of the fact that in some the 

 current was continuous in the two pieces and not in others. Only 

 one developed hydranths simultaneously on the free ends. Eleven 

 formed a hydranth on one end only. 



These experiments, as a whole, show that double pieces usually 

 form one hydranth only (Fig. 19, D), or first one and then another 

 later on the other end, regardless of the direction of the graft, or 

 the flow of the currents. 



6 THE EFFECT OF INTERRUPTING THE NORMAL PROCESS OF 

 HYDRANTH FORMATION 



Driesch ('97) first showed, in his researches on Tubularia, that 

 when the formation of the hydranth is interrupted by separating 

 the two tentacle ridges shortly after they appear, the method of 

 completing the hydranth is not always the same. He has described 

 four methods of regulation: (i) The "Regenerationsmodus" 

 where the hydranth emerges with the original proximal tentacles, 

 and later develops a new distal row; (2) the "Ersatzanlagemodus" 

 where the coenosarc in front of the proximal row elongates and a 

 new distal row appears before the hydranth emerges; (3) the 

 "Auftheilungsmodus" where the proximal tentacles divide, form- 

 ing the distal row from their distal ends; (4) the "Auflosungs- 

 modus" where the proximal row disappears entirely and a new 

 anlage forms. I repeated these experiments ('00) suggesting that 

 the diff^erence in the method of completion of the hydranth on the 

 proximal piece was due to the degree of differentiation of the pri- 

 mordia. If the distal row of tentacles was removed soon after the 

 red material had begun to collect in the two rows, the fourth 

 method was invariably followed, i. e., the first proximal row dis- 



