REGENERATION IN TUBULARIA CROCEA. 29 1 



This seeming difference between the two species may possibly be 

 due to the fact that Tubitlaria crocca, which lives in cold water, 

 regenerates very slowly and, therefore, comparatively slight dif- 

 ferences in the rate of regeneration at the oral and aboral ends of 

 the stem can be readily noted. Tubitlaria incscinbrvantlicinnni, on 

 the other hand, lives in much warmer water and its regeneration 

 takes place so quickly that it is difficult to detect slight differences 

 in the rate of development of the polyps at the cut oral and 

 aboral surfaces. 



In a variation of the above experiment, a piece of silk thread 

 was tied tightly around the stem about 2 mm. below thehydranth, 

 and another piece was tied about 30-40 mm. below the first. 

 Both ends of a long piece of stem were, therefore, closed at prac- 

 tically the same time in such a way that no regeneration was 

 possible from either end of the piece. After the ends had been 

 tied, the stem was cut transversely through the middle as in Fig. 

 I, B, C, in order to ascertain whether subsequent regeneration 

 from the cut surfaces, B, and C, would be hastened in comparison 

 with the rate of regeneration from similar surfaces of pieces of 

 stem of the same length, cut at the same time, but not closed 

 artificially at one end. The control pieces of stem were kept in 

 the same dishes with those used in the experiment, and both sets, 

 therefore, were under the same external conditions. 



Eight long pieces of stem were used in this experiment. Two 

 days after the operation, tentacle anlagen had appeared at the 

 cut ends of all of the sixteen pieces, but they were not as well 

 developed on the aboral end, B, of the anterior piece as they 

 were on the oral surface, C, of the posterior piece. At this time 

 there was no indication of any regeneration at the aboral sur- 

 face of the anterior piece in the control set of stems, although in 

 some cases complete hydranths, in other tentacle anlagen, were 

 present on the oral end of the proximal pieces. On the third 

 day after the operation, polyps were found on the oral end, C, of 

 all of the proximal pieces, both in the control and in the tied 

 stems. The development from the aboral surface, B, of the an- 

 terior pieces, however, did not keep pace with that at the oral end, 

 C, of the proximal pieces, as at this time only two of the pieces of 

 stem tied at one end had produced hydranths at the aboral sur- 



