4IO ,L. H. HYMAX. 



the six or eight stems in each experiment were selected so as to be 

 of similar diameters. 



The following generalizations may be drawn from the data 

 given in Table I.: 



1. In all cases the rate of oxygen consumption per unit volume 

 is higher in the apical than in the basal pieces. This result is in 

 harmony with differences in rate of regeneration and in electrical 

 potential which exist along the stem of Tubularia (cf. Hyman, 

 '20). 



2. There is an inverse relation between the diameter of the 

 stems used and the rate of oxygen consumption, the rate being 

 higher the smaller the diameter of the stems. This agrees with 

 the general law that in animals respiratory rate is inversely 

 proportional to size. 



3. In general it appears that the respiratory differences 

 between apical and basal pieces are greater the smaller the 

 diameter of the stem. This indicates that the respiratory gradi- 

 ent is steeper the more slender the stem. 



These conclusions are considered further in the discussion. 



EXPERIMENTS ON REGENERATION. 



Data on certain questions regarding regeneration which were 

 obtained on Tubularia marina at Pacific Grove, California, in 

 1922, on Tubularia crocea at Woods Hole, Massachusetts, in 1924, 

 and on Tubularia sp. at Swan's Island, Maine, in 1924 are herein 

 presented. Owing to the large amount of work that has already 

 been done on the regeneration of Tubularia, it does not seem 

 necessary to present these data in detail. For the most part 

 general statements will be made. 



The expression "rate of regeneration" is defined and used to 

 mean the time which elapses between the act of cutting and the 

 attainment of a condition of equilibrium. Since in pieces of 

 Tubularia of the size employed complete regeneration of a hy- 

 dranth at the apical end of the piece always occurs, a condition 

 of equilibrium is here synonymous with the completion of a 

 hydranth. Practically, however, it is difficult or impossible to 

 determine the exact time at which the regenerated hydranth is 

 complete. As is well known, the new hydranth forms within the 



