Experiments on Polarity in Tubularia. 583 



free end of the stolon. These hydranths were formed In the 

 usual way and developed as rapidly as oral polyps after the 

 primordia appeared, but a longer time elapsed before they began 

 to form than in the case of aboral cut ends of pieces stuck into 

 sand. All the pieces of this kind (14) produced hydranths and 

 in several cases the hydranth degenerated and regenerated several 

 times in the course of a month. The same result was obtained 

 when uncut pieces bearing stolons were tied. When the stolons 

 were cut off, a hydranth was formed very quickly at the cut end 

 (oral) of young (recently grown) stolons; pieces of old stolons 

 usually regenerated a hydranth at the oral end and a stolon at 

 the aboral end. 



Experiment 16. The above experiment suggested the follow- 

 ing: Several long uncut stems were ligatured at two or three places 

 to see whether hydranths would develop between the ligatures, 

 i. e., in parts of the coenosarc cut off from the rest of the piece, but 

 with the ends not exposed to sea water. 



In the first set 8 stems were used and one oral hydranth de- 

 veloped between the ligatures after 6 days. In the second 7 

 stems were ligatured. One oral hydranth appeared after 7 days, 

 one aboral after 13 days, and another oral after 20 days. The 

 first set might have yielded further results if they had been 

 observed for a longer time. Experiments 15 and 16 show that a 

 hydranth may be formed at an end of stem or stolon not exposed 

 to sea water by cutting the perisarc, but the development of such 

 hydranths is long delayed. The absence of a hydranth, however 

 removed, whether by natural degeneration, cutting, burying in 

 sand or ligaturing, seems to lead to the regeneration of another 

 hydranth, but the rate of regeneration depends on other condi- 

 tions. 



Experiment 17. In connection with Experiment 2, it occurred 

 to us rather late, when little available material was at hand, that 

 long double-headed pieces should be cut in the middle, without 

 removing the hydranths, to see whether the two cut ends would 

 behave alike or differently. Only one piece regenerated and that 

 produced stolons on both cut surfaces, regeneration being most 

 rapid at the aboral end of the distal half of the piece. 



