Experiments on Polarity in Tubularia. 579 



The second series developed slowly as has been said, owing 

 to colder weather. Even the long pieces, kept 48 hours before 

 cutting, had not pushed out their polyps, although the primordia 

 had begun to appear. In the 24-hour series, the primordium 

 was so far developed that it could be easily seen, and after 36 and 

 48 hours the hydranths were fully formed and ready to emerge. 

 Whether we can correlate with this latter condition the relatively 

 more rapid development of the pieces that lay just behind the 

 oral region is perhaps questionable, but it appears not improbable. 



The main result of the experiment is negative; for, no satis- 

 factory evidence was obtained to show what changes are taking 

 place in the stem during the formation of the oral hydranth, 

 except perhaps in the case of the pieces immediately behind the 

 hydranth-forming region in the series cut after that region was 

 well developed. It will be noted that there are fewer double- 

 headed short pieces in these sets than in those cut from double- 

 headed long pieces. Since the shortness of the pieces may have 

 caused a delay in development and thus introduced another factor, 

 we tried the following experiment in which long pieces were used. 



Experiment 12. Here long pieces were cut from the stem, 

 and after certain intervals, the oral end was cut off at two or 

 three different levels, and the time required for the development 

 of a polyp was noted and compared with that in a check series 

 in which the old hydranth was cut off at the time of the second 

 operation on the long pieces. In one set the long pieces were 

 kept 12 hours after the old head had been cut off, and then about 

 4 mm. of the oral end was cut off in some pieces, in others about 

 15 mm., and in others a much longer piece. Check pieces were 

 cut at the first and last of these levels at the same time. No 

 difference in the time of regeneration at the three levels or in the 

 check experiment could be detected. 



Other pieces of the same set were cut off after 17 hours and 

 gave the same result. In another set the long pieces were kept 

 24 and 36 hours (when the primordia of the polyps had appeared) 

 and the oral ends were then cut off at three levels, {a) just behind 

 the primordium, {h) 10 to 20 mm. further back, and {c) far back 

 nearer the base of the stem. Check series were also made. Here 



