THE AXIAL GRADIENTS IN HYDROZOA. 42 1 



quoted a considerable body of evidence in support of this general- 

 ization. Since then I have obtained additional evidence (un- 

 published) of the inverse relation between respiratory rate and 

 size in Corymorpha, starfish, nudibranchs, and tadpoles; and 

 other data have appeared in the literature (e.g., Smith, '25). 

 The relation here found in Tubularia between rate of regeneration 

 and age probably also is of general application. Przibram ('07) 

 gives a discussion of this matter and reaches the generalization 

 that the rate of regeneration is more rapid the younger the 

 animal and declines with age. 



Not only is there a relation between rate of regeneration 

 (time between cutting and completion of oral or apical structures) 

 and respiratory rate but the amount of tissue regenerated in a 

 given time appears also to be dependent upon metabolic rate. 

 This applies both to axial differences and age differences. In 

 general the more apical the level from which the piece is taken 

 the larger is the size of the oral or apical end regenerated, and 

 the greater the total mass of regenerated tissue. This result 

 cannot be ascribed to differences in mass of pieces from different 

 levels for it also holds when the pieces are of equal mass. It 

 is shown in this paper that in Tubularia, the regenerated oral 

 hydranth is larger on apical than basal pieces, when the length 

 and apical diameters of such pieces are the same. Driesch ('99) 

 and Child ('07) had previously noted that the length of the pri- 

 mordium of the oral hydranth is greater the more apical the piece. 

 A similar relation between level and the size of regenerated 

 apical structures or total amount of tissue regenerated was ob- 

 served by Billard ('04) in Obelia, Child ('03) in Cerianthus and 

 Planaria ('n) and Morgulis ('07) in annelids. 



The amount of tissue regenerated in a given time is also 

 greater the young : ; (smaller) the organism, relative to its size. 

 This is shown to be the case in Tubularia, pieces from smaller 

 stems producing relatively larger hydranths in a shorter time 

 than pieces of equal length from large stems. A similar relation 

 between age and rate of formation of new tissue was found by 

 Zeleny ('07), Ellis ('08), and Scott ('09). 



A third factor appears to be involved as regards the amount 

 of tissue regenerated in a given time. This factor is the degree 



