128 



INDIVIDUALITY IN ORGANISMS 



EXPERIMENTAL CONTROL OF SPATIAL RELATIONS OF 

 PARTS AND OF THE RANGE OF DOMINANCE 



The dimensions and distance relations of parts along 

 an axis can be altered by altering the metaboHc rate in 

 the dominant region or throughout the organism and 

 so increasing or decreasing the length of the gradient. 



Ill III 



a 



III W 



60 



r 



I e a 81 



ill II 



62 



61 



Figs. 60-62. — Different lengths of hydranth primordium in recon- 

 stitution of pieces of Tubularia: Fig. 60, length at medium metabolic 

 rate; a, b, c, d, the four regions of the primordium; Fig. 61, length at 

 high metabolic rate; Fig. 62, length at low metabolic rate. 



In Tubularia the reconstitutional development of a 

 hydranth is a transformation inside the perisarc of the 

 terminal region of the piece into a hydranth without 

 outgrowth of new tissue from the cut surface. In the 

 early stages of this process (Figs. 60-62) the two rows 

 of tentacles arise as two series of longitudinal ridges 

 (Fig. 60, b, d), usually distinguishable from other parts 



