THEORY OF AXIAL GRADIENTS 273 



time of regeneration of the shorter and the longer pieces are 3.2 

 hours in favor of the larger piece in both series. 



In table 5 the ratio of the sizes of the pieces was 1 : 4 and the 

 averages are in series A: for the shorter apical pieces 83.8 hours, 

 and for the longer basal one 79.1 hours, with a difference of 4.7, 

 while in series B the averages are: for the longer apical piece 

 75.1 hours, and for the shorter basal piece 80.0, with a difference 

 of 4.9. 



In any of these cases there was no evidence of the existence of 

 level or regional differences on the stems of Tubularia. 



CONCLUSIONS 



Child has based his theory of the 'metabolic gradients' on the 

 assertion that if a stem of Tubularia is cut into two pieces the 

 oral end of the apical piece will regenerate a hydranth more rap- 

 idly than the oral end of the basal piece. The differences in the 

 time of regeneration observed by him were so small that they 

 seemed to lie within the limits of error of such experiments. 



The writer repeated Child's experiments and found this sus- 

 picion justified. The rate of regeneration of the oral hydranth 

 of an apical piece is on the average identical with the rate of 

 regeneration of the oral hydranth of the basal piece. If in one 

 series the average is in favor of the apical piece, in another the 

 reverse may be found. 



There is no evidence of the existence of level or regional differ- 

 ences of the rate of regeneration in the stem of Tubularia, and as a 

 consequence there is no basis for the theory of 'axial gradient' 

 in this species. 



I have to acknowledge my thanks to Dr. Jacques Loeb, who has 

 suggested and directed the present work. 



