294 HELEN DEAN KING. 



Series i .- - On June 24, twenty experiments were made in 

 which a branch" was cut off about I mm. from its origin in the 

 stern, and then the anterior end of each stem was removed by a 

 transverse cut leaving a piece from 10-20 mm. above the place 

 of union with the branch (Fig. 3). In one case, a 

 hydranth developed on the cut end of the branch two 

 days after the operation, and at the same time a 

 polyp also formed on the oral end of the main stem 

 which in this instance was 20 mm. in length above 

 the origin of the branch. In all other individuals at 

 this time tentacle anlagen had formed at the oral end 

 of the stem, but there was no indication of the devel- 

 opment of a hydranth at the cut end of any of the 

 branches. On June 27 hydranths were found at the 

 oral end of all of the stems and also on the distal 

 end of four branches ; all the remaining branches 

 had well developed tentacle anlagen excepting one 

 which showed no signs of regeneration during the 

 course of the week that the hydroids were kept. In 

 this set of experiments, therefore, with the exception of the one 

 case noted, regeneration of a hydranth took place at the distal 

 end of the long stem before a polyp formed at the oral end of the 

 short branch. 



The results of this set of experiments might possibly be con- 

 sidered to be due to the fact that the longer piece exerted some 

 kind of an influence over the shorter piece that would tend to 

 alter the polarity of the shorter piece and thus retard develop- 

 ment from its cut oral surface. That a larger piece of a hydrozoa 

 can influence the polarity of a smaller piece is shown unques- 

 tionable in grafting experiments that I made on Hydra viridis 

 (King, 6) in which the larger component of the graft either 

 absorbed the smaller component or formed a permanent union 

 with it. In the latter case, the polarity of the smaller piece was 

 completely reversed, if necessary, in order that a structure 

 might regenerate on its cut surface that would produce a normal 

 polyp. Another factor that might, possibly, cause a delay in the 

 development of a hydranth from the cut surface of the shorter 

 piece is the length of the piece. Morgan has shown that in 



