Experiments on Polarity in Tubularia. 563 



is complicated by another factor, namely, the reduction in the 

 length of the hydranth-forming region, which in itself seems to 

 involve a delay in the development. 



Sixth. The formation of new pigment is not characteristic of 

 the new hydranth alone; but in the development of a new stolon 

 a large amount of new pigment is formed, and at a time when there 

 is none present in the circulation. 



We may now examine in the light of these statements the argu- 

 ments which Loeb believes are in favor of the red pigment being 

 a factor in the development of new hydranths.^ 



With the following statements in Loeb's paper we cannot 

 agree : 



First. On p. 154 Loeb states, "I found further that at that 

 end at which a new polyp forms, the formation of this organ may 

 be recognized beforehand from the fact that red pigment granules 

 collect at this end in relatively great density. New pigment 

 granules are transported by a current of fluid to this end, and 

 evidently remain lying or stuck in the neighborhood of the cut 

 surface. The stream of fluid is kept up by ciliary movement. I 

 expressed at that time the opinion that such a transportation of 

 materials by the stream of fluid toward the cut end is one of the 

 conditions of the formation of organs in Tubularia, and that the 

 polarity of the Tubularia stem, i. <?., the fact that the polyp forms 

 earlier at the oral pole, depends on the fact that the 'organ-form- 

 ing' substances (possibly the red pigment granules) collect in 

 suflicient quantity sooner at the oral than at the aboral end." 

 We find on the contrary that the end where the polyp is to develop 

 begins to thin out in preparation for the formation of the polyp 

 and the primordia of the tentacles may be laid down before the 

 red pigment begins to accumulate. Loeb speaks of the current 

 as passing forward, and this appears to lend support to his view; 

 but it should not be overlooked that the current flows backward 

 on the other side of the stem and the same argument could be 



'Concerning Dynamic Conditions which contribute toward the Determination 

 of the Morphological Polarity of Organisms. University of California Publications. 

 Physiology, Vol. I, Nos. 16 and 17. 1904. 



