90 C. M. CHILD. 



that wherever new development of a hydranth or an orderly 

 axial complex occurs the characteristic gradients are found to be 

 present and after a period of resorption, redifferentiation and 

 rejuvenescence following the stage of medusa-bud formation the 

 general colony gradient may reappear simply as a physiological 

 consequence of the order in which development, senescence, 

 death or resorption, and new development occur in different parts 

 of the colony. In other words, the new colony gradient in such 

 cases is a physiological consequence of the existence of the original 

 gradient. Of course, in some cases, environmental factors may 

 play a part in altering the original relations and so in modifying 

 the form and order of the colony. 



It is of interest to note that Cast and Godlewski ('03) studying 

 the form regulation of Pennaria cavolinii found a general colonial 

 gradient in rate of regeneration of hydranths. After removal of 

 the hydranths from a colony or axial complex, development of 

 new hydranths decreased in rate basipetally in the colony as a 

 whole and in each axial complex. Later degeneration of the 

 regenerated hydranths began in the most basal regions and pro- 

 ceeded a greater or less distance apically, but the most apical 

 hydranths persisted, grew and budded at the expense of these 

 other more basal parts. Both of these gradients, the regeneration 

 gradient and the degeneration gradient, indicate that the funda- 

 mental physiological activity of the protoplasm is greater apically 

 and decreases basipetally in the colony as a whole and in each 

 axial complex. In short, these regulatory phenomena constitute 

 still another line of evidence for the existence of the physiological 

 gradients. 



And finally, I am permitted to state from unpublished work 

 that Dr. A. W. Bellamy and Dr. L. H. Hyman, working inde- 

 pendently, have found gradients in electric potential in hydroid 

 colonies of various species. These electrical gradients corre- 

 spond to the gradients in susceptibility, reduction of permanga- 

 nate and rate of regulation. In vigorous, growing colonies the 

 apical region of the colony is galvanometrically negative to all 

 other levels, the apical region of each axial complex is negative 

 to all other parts of that complex, and the apical regions of the 



