RECONSTITUTIONAL PATTERNS IN EXPERIMENT 371 



ample, in Corymorpha pieces or aggregates radial pattern may develop 

 quite independently of the original radial pattern, but in stem pieces 

 isolated by transverse section the longitudinal entodermal canals of the 

 stem which are parts of the original radial pattern are factors in localizing 

 tentacle development. 



SOME SPECIALLY SIGNIFICANT CASES OF NEW PATTERNS 

 IN RELATION TO SECTION 



Under natural conditions the dominance of the apical hydranth of 

 Corymorpha prevents development of lateral hydranth buds, and the hy- 

 dranth-stem axis remains permanently unbranched. A simple lateral 

 transverse section part way through the Corymorpha stem closes in a few 

 hours but may become the locus of development of a new hydranth and 

 stem, provided the original hydranth is removed. In experiments involv- 

 ing several hundred animals the frequency of hydranth development from 

 a simple incision, with removal of the apical hydranth at the same time, 

 was 56.7 per cent at a level near the distal end, 26.7 per cent at a middle 

 level, zero at a proximal level; with the apical hydranth present and in 

 good condition it was zero at all levels (Child, 1927^, 1929a, 1932a). How- 

 ever, even a small lateral incision, with edges lacerated by repeated small 

 cuts so that heahng does not occur so rapidly and smoothly, becomes a 

 new hydranth-stem axis after healing in almost 100 per cent of the cases 

 if the original hydranth is removed (Fig. 125, A-C). Later an outgrowth, 

 and in some cases a differentiated basal region, may develop from the 

 opposite side of the original stem (Fig. 125, D). In these forms, as in 

 other Corymorpha reconstitutions, hydranth development is not from a 

 cut surface but from a region activated by the lacerated incision ; develop- 

 ment begins only after the closure of the incision. The activated region 

 determines a new gradient, at first radial, as in buds generally, and be- 

 coming longitudinal by differential growth, and acts as an inductor, some- 

 times being effective across the original stem in inducing development of 

 a basal region where there is no incision or other injury. Under slightly 

 inhibiting conditions the lacerated incision may give rise to a basal region 

 with perisarc and holdfast buds instead of a hydranth (Fig. 125, E). 



New axes have been localized in a somewhat similar manner in the 

 elongated actinian Harenactis attenuata (Child, 1909c, 1910c). After re- 

 moval of muscles and mesenteries from the inside of short pieces isolated 

 by transverse sections from levels proximal to the esophagus contraction 

 brings distal and proximal cut surfaces of the body wall of the piece to- 



