4i8 



L. H. HYMAN. 



TABLE V. 



DIMENSIONS OF REGENERATED ORAL HYDRAXTHS ON PIECES OF THE SAME LENGTH 

 AND DISTAL DIAMETERS BUT FROM DIFFERENT LEVELS. 



Figures, units of the micrometer scale. 



DISCUSSION. 



The foregoing facts together with others available from the 

 literature support the conception of the existence of a metabolic 

 gradient along the main axis in Tubularia and other lower forms; 

 and of a relation between this gradient and the rate of regener- 

 ation. 



It is shown in this paper that the rate of oxygen consumption 

 in the stem of Tubularia is higher in apical than in basal levels. 

 It thus appears that there exists a gradation in respiratory rate 

 along the stem of Tubularia. Similar respiratory gradients 

 along the main axis were previously reported for other lower 

 invertebrates: Corymorpha, Grantia, Planaria, several annelids 

 (Hyman, '22, '23, '25, Hyman and Galigher, '21). It is reason- 

 able to believe that they are of universal occurrence among at 

 least the lower Metazoa. We believe that such differences in 



