TIIK AXIAI. <;i<Al>II<:.\TS IN II YDKO/O A. }ll 



perisarc and llu 1 linii' of completion of its format ion in situ 

 would furnish the- most accurate measure of rate of regeneration 

 if such time could be determined. For practical purposes one 

 generally notes the time at which the finished hydranth emerges 

 from the top of the old perisarc. There is no doubt some error 

 in such a procedure for in some cases at least such emergence 

 may be greatly delayed by irregularities in the perisarc through 

 which the hydranth must force its way. However, no better 

 criterion of the time of completion of regeneration has been sug- 

 gested by anyone and the time occupied by the regeneration 

 process will here be used to signify the time between cutting and 

 the emergence of the completed hydranth. 



In all regeneration experiments straight healthy unbranched 

 stems were employed. These were invariably cut as follows. 

 The hydranth and upper millimeter or two and the basal portion 

 of the stem were removed and discarded. The remaining stem 

 was then cut as desired. 



The regeneration of only the oral hydranth i.e., the hydranth 

 which forms at the apical end of each piece was studied. Unless 

 specifically stated otherwise, all statements refer to this hydranth 

 only. No study was made of the regeneration of aboral hy- 

 dranths. 



1. Rate of Regeneration of Halves of the Stem. In such experi- 

 ments the stem is divided into halves and the time between 

 cutting and emergence of oral hydranths noted for apical and 

 basal halves. As above stated the observations refer only to 

 regenerated oral hydranths. In a previous paper (Hyman, '20) 

 1 presented a considerable mass of data on this matter using 

 Tubularia crocea. These experiments showed that the time be- 

 tween cutting and emergence of oral hydranths is markedly 

 shorter in apical than in basal halves. Since writing that paper 

 the same result has been obtained with T. marina and with the 

 Maine species. The result on T. crocea was also again verified. 

 In Table II, I present a typical experiment on T. marina. 



2. Rate of Regeneration of Thirds of the Stem. A few experi- 

 ments on this point were performed on T. marina and on the 

 Maine species. The result was found to be different in the two 

 species. In T. marina, the apical third regenerates first, the 



