REGENERATION IN TUBULARIA CROCEA. 



293 



June 23, three of the ten proximal pieces of stem bearing aboral 

 hydranths had also developed hydranths at the oral end ; while 

 the oral end of two other pieces of stem showed well developed 

 tentacle anlagen which developed into 

 hydranths on the following day. No 

 further changes took place in any of 

 the pieces although they were kept for 

 some ten days longer. 



It is seen from the above experiments, 

 that the presence of a hydranth at the 

 aboral end of a piece of the stem of 

 Tubularia delays, but does not prevent, 

 the development of a hydranth at the 

 oral end of the piece. This result can- 

 not be due simply to the fact that the 

 proximal end of the piece was closed 

 by the presence of the aboral polyp, 

 because, in the previous set of experi- 

 ments, it was shown that closing the 

 aboral end of a piece of stem by tying 

 does not delay the development of a 

 polyp at the oral end. It seems prob- 

 able that the polarity of the piece was 

 changed, for a time at least, by the 

 presence of a hydranth at its aboral end 

 and, therefore, the influences for hydranth 

 formation at the freshly cut oral surface 

 were not strong enough to bring about the development of a 

 polyp for some days. 



II. EXPERIMENTS ON BRANCHING STEMS. 

 The following series of experiments were made in order to as- 

 certain whether the development of a hydranth on the oral end 

 of a stem will influence the rate of development of a hydranth 

 on the distal end of a long or of a short piece of a branch, and 

 also to determine what conditions are necessary in order that the 

 formation of a hydranth at the one place will prevent the forma- 

 tion of a hvdranth at the other. 



FIG. 2. 



