THE RANGE OF DOMINANCE 



^33 



length this stolon gives rise to a hydranth at its tip. 

 This is a process of reproduction like that occurrincr i,^ 

 nature (Fig. 43, p. 90), and differs from it only in tliat 

 the distance of the second hydranth 

 from the first is less in the pieces 

 than in the animal under natural 

 conditions. This difference indi- 

 cates that, as might be expected, 

 the range of dominance of the 

 apical region is less in the experi- 

 mental piece than in the whole 

 animal in nature. 



In most pieces, however, the 

 dominance of the apical region is 

 insufficient to inhibit the establish- 

 ment of a well-marked new gradient 

 in relation to the cut basal end of 

 the piece, and so the formation of 

 a hydranth usually occurs at this 

 end also, as in Fig. 63. The 

 development of this hydranth is 

 usually delayed, as compared with 

 that of the apical hydranth, be- 

 cause the establishment of the new 

 gradient is more or less retarded 

 by the gradient already existing in 

 the original direction, and the 

 shorter the piece the greater the 

 delay, because in shdrter pieces the dominance of the 

 apical region is more complete, or, in other words, the 

 gradient from the apical region is more marked at the 

 basal end and therefore inhibits or retards to a greater 



64 



Figs. 6;^, 64. — Recon- 

 stitution of longer pieces 

 of Tuhularia: Fig. 63, 

 usual result of recon- 

 stitution with hydranth 

 at basal end; Fig. 64, 

 reconstitution with 

 stolon at basal end. 



