266 MARIO GARCIA-BANUS 



hydranth sooner than the aboral end. Child in his experiments^ 

 cut the stems of Tubularia in two or three pieces of equal length, 

 and states that in such cases the oral end of the most apical 

 piece will regenerate a hydranth sooner than the oral end of the 

 most basal piece. This is the actual basis for his theory of ' axial 

 gradient.' 



The differences found by Child between the times of emergence 

 of the oral hydranths of the two pieces are, however, so slight 

 that the suspicion arises that they may be merely within the 

 limits of error and individual variation. 



As a matter of fact, only in one single case of those that he 

 presents, is there a marked difference between the time of the 

 regeneration of the oral hydranths of the apical and basal pieces. 

 And in this case the average is based on the observation of only 

 eight individual stems. The apical pieces give an average time 

 of emergence of the oral hydranths eqp-al to 27 hours, while for the 

 basal pieces the average is 36.5 hours. In all the other cases 

 which he gives, the differences are far from being so marked. 

 Thus in one case the averages for the hydranth formation of 

 eight stems were 38 hours for the apical pieces and 39 hours 

 for the basal pieces, while in a third case the averages were 42 

 for the apical pieces and the same number 42 for the basal ones! 

 In the case of the stem cut into three pieces of equal length 

 the averages for the oral hydranth formation are for one of the 

 series of twenty stems, 42.5 for the most apical piece and 44 for 

 the most basal one, and in another series of ten stems the averages 

 are 117 for tE"e apical piece, 118 for the middle piece, and 120 for 

 the most basal one. 



The differences in all these experiments, except the first, are 

 so small that they may well lie within the limits of variation and 

 of error of such experiments. In order to be sure we repeated 

 Child's experiments to try to ascertain the foundation for his 

 conclusions. 



* Child, C. M., An analysis of form-regulation in Tubularia. IV. Regional 

 and polar differences in the time of the hydranth formation as a special case of 

 regulation in a complex system. Arch. f. Entwicklungsmech., 1907, 24, 1. 



