THE AXIAL GRADIENTS IN HYDROZOA. 363 



tically the same condition at Woods Hole in June and in 

 December and yields identical results at these two seasons of the 

 year. Banus further states that the "temperature during re- 

 generation was in New York 22 C., and in Woods Hole it was 

 about 15 C." Upon examination of Banus's tables, one finds 

 that the time interval between section and emergence of hy- 

 dranths is much too great for these temperatures. At a tem- 

 perature of 22 C., apical pieces of Tubularia produce hydranths 

 as early as 36 hours after section and the great majority of such 

 pieces will have completed regeneration in 48-60 hours, yet in no 

 case do any of the pieces recorded in Banus's tables regenerate in 

 less than 53 hours and the majority of them require more than 

 60 hours. Even at a temperature of 15 C., the times given by 

 Banus are surprisingly long, since I found that at 12 C., the 

 majority of the apical pieces will regenerate within 70-80 hours 

 (see Table IV.). It is therefore evident that in Banus's experi- 

 ments some factor is acting to delay the time of regeneration 

 of the apical pieces, whose regeneration precedes by an average 

 of i o to 12 hours, according to my findings, the regeneration of 

 the basal pieces. 



The cause of the delayed regeneration in Banus's experiments 

 lies in all probability in his method of cutting the apical pieces. 

 In reply to my inquiry concerning the level of the stem from which 

 he cut the pieces, Banus made the following statement: "the 

 most distal cut was usually made as near as possible to the 

 hydranth without including any part of it." Such a method of 

 procedure explains the aberrant results obtained by Banus. It 

 has long been known that the short stalk below the hydranth of 

 Tubularia is incapable of regeneration. When the apical pieces 

 are cut in the manner described by Banus, this stalk forms the 

 distal end of such pieces. It dies and disintegrates, thereby 

 markedly delaying the regeneration and time of emergence of 

 oral hydranths on these pieces. I shall present evidence in 

 this paper (see Table XI.) that when the apical pieces are 

 cut in such a way that their distal ends are just below the 

 base of the original hydranth, the time of emergence of the 

 oral hydranth is greatly delayed and falls behind that of the 

 basal pieces. Hence when such a procedure is followed, all 



