RECONSTITUTIONAL PATTERNS IN EXPERIMENT 415 



of these also in pieces that failed to stand continuously on end.^* In these 

 experiments many of the unipolar forms finally developed basal ends from 

 the ends determined as proximal by the differential exposure, whether 

 originally proximal or distal. 



In Corymorpha pieces lying on the side, particularly in bipolar pieces, 

 a basal region with perisarc and stolon buds frequently develops quite 

 independently of section from the side in contact (Fig. 1^1, A, B); or two 



Fig. 141, A-D. — Development of bases in bipolar forms of Corymorpha (from Child, 

 19266). 



basal ends sometimes develop, producing forms of cruciate type (Fig. 141, 

 C). The fact that these basal ends developing from lateral regions in con- 

 tact are localized midway between the two hydranths of bipolar forms if 

 these are approximately equal suggests that the two hydranth-stem gra- 

 dients determine this region as the lowest gradient-level in the piece and 

 that the differential between side in contact and free side plays a part in 

 determining the basal region laterally instead of about the whole circum- 



^5 The naked stems of large Corymorpha individuals are several millimeters in diameter 

 when contracted, and short pieces usually remain more or less contracted for some hours after 

 section. Reconstitution is so rapid that the hydranth primordium usually becomes directly 

 visible within 24-30 hours; consequently, this length of time is usually sufficient to determine 

 position of the hydranth or hydranths. Some of these experiments were reported in an earlier 

 paper (Child, 19 266). For further discussion of hydroid reconstitution in relation to o.xygen 

 see Barth, 1940, "The process of regeneration in hydroids," Biol. Rev., 15. 



