570 T. H. Morgan and N. M. Stevens. 



change in polarity had occurred. After three days eight of the 

 pieces had polyps on the old oral ends and three had stolons on 

 the old aboral ends (where the new polyp had developed); two 

 pieces had heads on the old aboral end; one had a head on each 

 end, and eight had not yet regenerated. After another day the 

 record of these pieces was as follows: Twelve had polyps on the 

 old oral end; seven had polyps on the old aboral end (six of these 

 had oral heads also); live had stolons on the aboral end (of these 

 four had a polyp on the old oral end and one had none). After 

 another day fifteen had polyps on the old oral end; eight had 

 polyps on the old aboral end; five had heads on both ends and 

 four had long stolons on the old aboral end. These results show 

 that despite the fact that the oral end was stuck into sand, the 

 original polarity of that end is markedly shown when it is cut off. 

 It is equally clear that the development of a polyp at the aboral 

 end has changed the condition of that end so that it is more likely 

 to produce a polyp (when it is cut off near the new aboral hydranth) 

 than before. Thus the polarity of the whole piece is not re- 

 versed but a new growing region is established at the old aboral 

 end. Another point in this connection is not without interest; 

 namely, that the end in the sand begins to form an oral polyp 

 in this species of Tubularia, and the process may go so far that 

 the hydranth is fully formed and ready to come out. It fails, 

 however, to emerge, unless removed from the sand, and is soon 

 absorbed. Meanwhile the aboral hydranth has regenerated. 

 We shall consider this point more fully later. 



Experiment 4. In order to show more precisely the limits of 

 the change that takes place at the aboral end as a result of the 

 development there of a polyp, the long pieces were cut into many 

 short ones. In the records given in Table^ FV aik^ V double- 

 headed pieces were used; in the second series. Tables VI and VII, 

 the oral ends of long pieces had been stuck into sand or vaseline 

 and kept there until the aboral polyp appeared. As, however, 

 in most cases, a hydranth forms at the oral end in sand or vaseline, 

 such pieces are practically double-headed pieces. The pieces 

 were then cut up into shorter ones varying from 5 mm. to 10 mm. 

 or more in length. The development of the shortest pieces may 



