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



made to show that the aboral end should develop its polyp first, 

 because a current also flows in this direction! 



Second. By sticking the oral end in sand Loeb found that a 

 larger proportion of the pieces produced aboral hydranths, and 

 in a shorter time than when suspended freely in water. This 

 result is cited as an argument in favor of the "assumption" that 

 the red granules are "organ-forming substances;" but it is not 

 clear that the experiment has any bearing on this point. Loeb 

 appears to mean that since the red substance can not be used at 

 the oral end, which is embedded in the sand, that, therefore, it 

 can be used by the aboral end. If this is his meaning, it should 

 be pointed out that the original assumption has now taken a very 

 different form, and the polarity is accounted for not by the direc- 

 tion in which the current flows, but by an abundant supply of a 

 formative or nutritive substance. With this point of view, so 

 fundamentally diff"erent from the other, we are ready to agree, 

 provided that the nutritive substance is something else than the 

 red pigment. The experiment of ligating the stem, which Loeb 

 states that he carried out "during the last summer," had already 

 been performed by Driesch ('99) and by Morgan ('01), and the 

 theoretical questions involved were discussed by them. Loeb 

 states that in ligated stems, only polyps appear at the aboral end 

 and never "roots." While this is true in general, yet occasionally 

 a "root" develops at the aboral end in the California species of 

 Tubularia. There is, however, no such sharp distinction be- 

 tween stem and stolon as is implied by the use of the term "root," 

 since a stolon may produce a hydranth at its end in the same way 

 that one is produced at the end of a stem. If the stem is ligated 

 or has its oral end stuck into sand the stolon may produce a polyp 

 at its distal end. A fuller discussion of this property of the stolon 

 will be taken up in another connection. 



Third. Loeb concludes that "the ligation of a piece cut from 

 the stem of Tubularia results in the suspension of the polarity as 

 far as regeneration is concerned." On the contrary we shall bring 

 forward evidence to show that the polarity is altered mainly near 

 the region where the aboral polyp has developed, and that a 

 reversal or suspension of polarity does not extend throughout the 



