478 



C. M. CHILD. 



have been mutilated by the injury the arrangement of the stolon 

 buds is likely to be irregular, as in Figs. 14-18. 



Development of two apical or basal ends from the region of 

 injury is undoubtedly a result of determination by the injury of 

 two regions of activity instead of one. Duplication of this kind 

 has been very widely observed in many forms as a result of split- 

 ting or otherwise dividing a growing region into two. 



One of the most interesting results of these experiments is the 

 determination by the more distal levels of the new axis of a basal 

 region on the opposite side of the stem where there is no injury 

 (Figs. 5, 6, 8, 12). It is evident that the development of the distal 

 region of the new axis has in some way altered conditions in the 

 region of the stem which gives rise to the base, but it has been 

 shown that contact or nearness to the bottom and the action of 

 various inhibiting agents may alter conditions in the same direc- 

 tion in regions of the stem (Child, '26b, '27(1, b). This being the 

 case there is no good reason for supposing that the changes which 

 initiate the development of the basal end are anything more than 

 quantitative changes in physiological condition determined by the 

 presence of the new gradient. In the case of Fig. 8 in which the 

 apical hydranth takes up a more or less lateral position because of 

 the position of the piece, it, as well as the lateral hydranth, develops 

 a new basal end, perhaps with the assistance of the conditions re- 

 sulting from contact of the region concerned with the bottom. 



The new lateral axis develops the characteristic radial symmetry, 

 except in cases such as Fig. 5, in which the differential resulting 

 from proximity of the other hydranth determines mutual and op- 

 posed dorsoventrality. If we examine the facts, again without 

 theoretical prejudice, it appears that the radial symmetry of the 

 axis is primarily nothing more than likeness of all radii in a plane 

 perpendicular to the polar axis. The primary growing region 

 determined by the injury is more or less radially symmetrical be- 

 cause its activity decreases radially from a center and as it becomes 

 a definite outgrowth (Figs. 2, 3) its radial symmetry appears to 

 result from this radial differential and from the fact that a surface- 

 interior differential exists at all points. With the localization of 

 tentacles certain radii become different from others. The factors 

 concerned in tentacle localization have been but little investi- 



