314 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



development of a second bud within a certain distance transversely in 

 the parent body.^ 



The hydroid Tuhiilaria gives rise to buds and branches to a varying 

 degree in different species. The young animal, emerging from the gono- 

 phore, attaches to the substratum by its basal end; this spreads and be- 

 comes somewhat flattened; and, as the unbranched stem increases in 



1 



B 



D 



Fig. io8, A-D. — Tubularia. A, young individual with developing stolon; B, transformation 

 of stolon tip into hydranth after physiological isolation by increase in distance from dominant 

 hydranth; C, reconstitution of stem piece with hydranth distal and stolon proximal; D, bi- 

 polar reconstitution ("axial heteromorphosis"). 



length, one or more buds develop from the base and grow out as stolons. 

 The stolon represents a new gradient, with high end at the tip, but differs 

 from the stem in that it grows in contact with the substrate and remains 

 a growth gradient without evidence of differentiation as long as it remains 

 a stolon (Fig. io8, A).'' Both stem and stolon elongate; and when a cer- 

 tain length, varying with physiological and external conditions, is at- 



^ The experimental literature on hydra is extensive. The following papers are in part di- 

 rectly concerned with the problem of dominance and budding: Hyman, 1928; Weimer, 1928, 

 1932, 1934; Rulon and Child, 1937a; they also give references to earher literature. 



' Child, 1907(7, igigd, ig2id, 1923a; Child and Watanabe, 1935/^ Watanabe, 1935c. 



