THE AXIAL GRADIENTS IN HYDROZOA. 



379 



number of apical pieces with oral hydranths than basal pieces. 

 The difference is always more marked in the early part of the 

 regeneration period; later the basal pieces may catch up with 

 the more tardy of the apical pieces with the result that the 

 number of regenerated basal pieces may in a few cases equal the 



TABLE IV. 



MASS EXPERIMENTS PERFORMED IN DECEMBER SHOWING RATE OF REGENERATION 

 OF APICAL AND BASAL HALVES OF STEMS OF Tubnlaria. 



Hrs. means number of hours elapsed since cutting; a, apical half; b, basal half; 

 figures under a and b give number of hydranths emerged at time indicated; asterisk 

 indicates first morning observation. 



number of regenerated apical pieces (exps. 27 and 35, Table IV.) ; 

 but in no case are the basal pieces in advance. 



(c) In all cases the apical pieces complete their regeneration 

 first. 



(d) When other factors are equal the rate of regeneration is a 

 function of temperature. 



(e) When other factors are equal, the rate of regeneration is a 

 function of the diameter of the stem. More slender stems re- 

 generate more rapidly than stouter stems. Thus in experiment 

 I, Table III., the pieces were cut from slender stems bearing 

 small hydranths; those in experiment 2, same table, from stouter 



