Experiments on Polarity in Ttibiilaria. 



S^l 



development of an organ shall be initiated, and is therefore the 

 cause of polarity. 



EXPERIMENTAL RESULTS. 



Experiment I. The following data will serve to show for this- 

 species, the frequency of the occurrence of aboral polyps in 

 pieces lying on the bottom of a glass dish containing sea water. 

 The polyp was cut from the oral end and the base cut off at vary- 

 ing distances above the stolon. 



In long pieces, measuring from lo to 25 mm. or more, \^ 

 about 5 per cent form aboral polyps (Fig. i); the rest 

 form stolons or do not regenerate at all at the aboral end. 

 When short pieces are cut off, measuring about 5 mm., 

 the percentage of aboral hydranths (double-headed 

 pieces) was larger, 8.5 per cent. When very short pieces 

 are cut off the same kind of incomplete structures that 

 have been described for the Naples and for the Woods 

 Hole species appear, and some of them are double 

 structures. In some cases the new head and stolon were J\. 

 cut off in order to see if a larger percentage of aboral fig. 1. 

 heads would develop, but this did not occur. In another 



series the new head only was cut 

 > 2 i 4 i off but this did not cause the aboral 



ends to produce hydranths; nor 

 were they produced when only the 

 stolon end was removed. 



Experiment 2. In order to see 

 what changes, if any, had been 

 produced by the development of 

 an aboral polyp in long pieces 

 having an oral polyp also, the 

 polyps at each end were cut off 

 and the piece cut in two in the 

 middle (Fig. 2). The pieces were 

 kept oriented so that the different ends were known. If the for- 

 mation of an aboral polyp at d had the same influence on the stem 

 as the formation of an oral polyp at a, the middle b c would be a 



\r 



r \ 



\ 



y^v 



r^\r 



Fig. 2. 



