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



Experiment 18. Delayed development in several series of 

 short pieces suggested the possibility that in this species light 

 might be a factor in the rate of regeneration. To test this three 

 sets of similar pieces were placed (a) in bright light near a w^indow, 

 (h) in diffuse light, {c) in total darkness. The rate of regenera- 

 tion for the three sets v^as the same. 



Experiment 1 9. The polarity of stolons was examined by 

 means of the following experiments: Young stolons that had 

 developed during four or five days and were stuck to the dish 

 were cut off, and each one produced a hydranth at the cut end. 

 Old stolons by which the Tuhularia had been attached to rocks 

 were also cut into pieces 5-10 mm. long and kept oriented. In 

 10 cases the polyp appeared on the end nearer the free end of the 

 stolon; in 18 cases on the end nearer the stem. Pieces cut from 

 recently grown stolons which had produced a polyp at the free 

 end, regenerated a hydranth at the end nearer the polyp. These 

 results show that the "polarity" of the stolon is not so marked as 

 that of the stem. When it is recalled that the free end of the 

 stolon may produce a hydranth if it does not come in contact with 

 a hard surface, the behavior of the two ends of the pieces is not 

 so remarkable. The free end of a stolon behaves in most respects 

 like an aboral, exposed end of a stem which also, under certain 

 conditions, produces a polyp. 



Experiment 20. In order to see to what extent changes pre- 

 paratory to the formation of a polyp have taken place at the aboral 

 end of a long piece that has regenerated an oral hydranth, pieces 

 that had within two or three days produced an oral polyp were 

 used. The tip of the aboral end was cut off (in most cases) and 

 the piece removed near the middle or nearer the aboral end. If 

 changes preparatory to the formation of a polyp had taken place, 

 we should expect the aboral polyp to develop first unless the origi- 

 nal polar conditions enabled the oral end to outstrip the aboral end 

 despite the advantage the latter might be supposed to have gained 

 by exposure to sea water. The results showed that in 29 cases 

 the oral polyp only developed, in 6 cases the aboral, in i case oral 

 and aboral at the same time, and in i case the aboral 6j hours 

 before the oral. A higher percentage of aboral polyps developed 



