Experiments on Polarity in Tiibularia. 565 



rest of the stem. It is true that by ligating the stem a more rapid 

 development of the aboral polyp is brought about, as Driesch 

 and Morgan had already reported. Even bending the stem 

 sharply produces the same effect, as Morgan has shown. This 

 question of the more rapid regeneration of the aboral polyp when 

 the oral end of the piece is closed will be fully discussed below. 



Fourth. Loeb states (p. 158), "The experiments so far de- 

 scribed had shown that by ligaturing a piece cut from the stem 

 of Tubularia one abolishes the difference between the oral and 

 aboral poles. The question arises whether one can go farther 

 and even reverse the polarity, z. e., whether one can force the 

 aboral cut end to form a polyp sooner than the oral end. This 

 is in fact possible, though this phenomenon does not manifest 

 itself with the same degree of certainty as the results of the liga- 

 ture experiments just described." The experiments, which he 

 believes demonstrate this point consist first in cutting off a piece 

 of the stem and ligating it in the middle; then after the aboral 

 polyp has developed, the half of the stem lying aboral to the 

 ligature is cut out, one cut end being near the ligature (the old 

 oral end), the other near the aboral polyp (the old aboral end, 

 but now that the polyp has appeared the new oral end). If the 

 latter end should produce "at least in a proportion of the cases" 

 a polyp sooner than the old oral end, this would show, Loeb 

 thinks, that the polarity of the piece has been reversed. He 

 found that the old aboral end (new oral end) produced a polyp 

 before the old oral end in ten cases and in five cases the reverse 

 occurred. From this Loeb concludes that the polarity of the 

 piece has been reversed. Such, however, is not the case. All 

 that the experiment really shows is that in some pieces the con- 

 ditions are more favorable for the development of the polyp at 

 the new oral end (old aboral end), where the polarity has been 

 changed, but the rest of the piece has retained its original polarity 

 as in the experiments in which the oral end of the piece was 

 buried in the sand. 



Fifth. Loeb's summary, which follows this experiment is as 

 follows (p. 159): "If we correlate all these observations, we 

 get the idea that the cause of the normal polarity which appears 



