THE AXIAL GRADIENTS IN HYDROZOA. 385 



further reduction in length." The apical pieces will therefore 

 regenerate later than the basal pieces only when they are reduced 

 below a certain minimum length. This minimum length is 

 very much less than any used in Banus's experiments. In order 

 to get the result mentioned by Child it is necessary to cut the 

 apical pieces as small as 2 mm. Yet Banns in "repeating" 

 Child's experiments has used no pieces less than 10 mm. in length. 

 In pieces as long as this, length makes very little difference; 

 according to Child's results and my own, the apical pieces will 

 regenerate oral hydranths earlier than the basal pieces, just as 

 when both pieces are of equal size. In his tables 3, 4, and 5, 

 Banus presents data on apical and basal pieces in which the 

 lengths of the pieces were: 10 and 20 mm., 10 and 30 mm., and 

 10 and 40 mm. Banus found that the longer pieces in all of 

 these cases, regardless of whether they are apical or basal, 

 regenerate oral hydranths slightly in advance of the shorter 

 pieces. 



With these results and statements of Banus I am quite unable 

 to agree. There is some truth in the statement that a longer 

 piece will regenerate slightly faster than a shorter piece with 

 apical end at the same level. Yet in the case of apical pieces, 

 the difference between pieces 10 and 20 mm. long is very slight 

 indeed, in fact, practically nil; but it is plainly marked in shorter 

 pieces, say 5 and 10 mm. long. In the case of the basal pieces 

 the difference in time of regeneration between 10 and 20 mm. 

 pieces is somewhat greater but here it must be remembered that 

 the apical end of a basal piece 20 mm. long is in these experi- 

 ments at a level 10 mm. more distal than that of a basal piece 

 10 mm. long, and the factor of level again comes into play. In 

 all cases in pieces exceeding 5 mm. in length, the apical pieces 

 will in general regenerate more quickly than the basal pieces, 

 regardless of their relative lengths; and a basal piece twice as 

 long as an apical piece will still regenerate more slowly than the 

 apical piece, notwithstanding the effect of length. 



I have repeated Banus's experiment on relatively long pieces 

 of unequal length and the results are given in Table VI. Three 

 pairs of experiments were performed. In one experiment*of each 

 pair the apical piece was half as long as the basal; in the other 



