282 HARRY BEAL TORREY. 



It will be noted that while a distal hydranth failed to develop 

 in contact with the substratum, it soon appeared when freed 

 from this contact, in spite of the presence of the large promixal 

 hydranth. On the supposition, however, that the result may 

 not have fully indicated the real state of affairs in the hetero- 

 morphic segment, the latter was sectioned at the level x. In two 

 days frustules were appearing at p' ; the original polarity of this 

 portion of the column was preserved. But frustules were also 

 appearing at d' , and two days later, were unmistakably defined. 

 In this latter region, therefore, the original polarity was reversed; 

 on a segment of a given polyp, not only had hydranth appeared in the 

 customary position of holdfast, but holdfast had appeared in the cus- 

 tomary position of hydranth. 



The outcome of this experiment recalls the reversal of polarity 

 which Loeb later obtained in Tubularia crocea when, after ac- 

 celerating the development of the proximal hydranth by inhibiting 

 the development of the distal, he cut a segment just distal to the 

 proximal hydranth and found that a proximal was now produced 

 more rapidly than a distal hydranth. 1 Morgan and Stevens 

 obtained a similar result on T. marina although the polarity of 

 the stem was reversed for but a very short distance from the 

 proximal end in this species. 2 



II. 



The suggestion, coming from the above experiment with Cory- 

 morpha, that section of the column between the hydranths merely 

 disclosed a reversed polarity that already existed but was not, 

 under the conditions, expressed in structural differentiation, led 

 to a number of similar experiments which showed that the original 

 result was in no sense exceptional. I will consider three series 

 of these experiments. 



In the first, nine heteromorphic pieces were sectioned at dif- 

 ferent levels to determine the extent to which each hydranth 

 might control the intermediate region in regeneration. In no. I, 

 the distal hydranth was removed by a cut immediately below it 



uger's Arch., 102 (1904), p. 152; trans, in Univ. Calif. Publ. Physiol., I 

 (1904), p. 151. 



*J. E. Z., i (1904). P- 559- 



