PHYSIOLOGICAL DOMINANCE 97 



at least to an advanced stage, in the complete absence 

 of other parts of the body. This independence is very 

 evident in Tubularia and Planaria. Pieces one or two 



Fig. 47. — Reconstitution of single and biaxial apical structures from 

 short pieces of stem of Tubularia, to illustrate independence of apical 

 region. 



millimeters in length cut from the stem of Tubularia 

 usually develop into hydranths with a very short stem 

 or partial hydranths with more or less of the basal region 

 absent (Fig. 47). The result depends on the condition 



