132 INDIVIDUALITY IN ORGANISMS 



therefore removal of the original hydranth favors physio- 

 logical isolation of basal regions of the piece. 



In Corymorpha the metabolic relations and the rela- 

 tions of the various parts of the body to the metabolic 

 gradients are essentially the same as in Tubularia, and 

 the demonstration of the metabolic gradients by means 

 of the susceptibility method in Corymorpha, where most 

 of the stem is naked, is not open to the objection which 

 might be raised in the case of Tubularia, where all parts 

 of the stem except the cut end are covered by the horny 

 perisarc, viz., that the reagent penetrates the tissues only 

 or chiefly from the cut end and so produces a death 

 gradient which is merely a gradient of penetration and 

 does not represent metabolic conditions. 



Some of the facts and their interpretations in terms 

 of metabolic gradients and physiological dominance 

 are briefly as follows:^ In pieces of Tubularia stem 

 eight or ten millimeters or more in length and with a 

 cut surface at each end reconstitution usually results 

 first in the development of a hydranth at the apical end 

 of the piece and later of a second smaller hydranth at the 

 basal end (Fig. 63). Occasionally pieces from vigorous 

 animals which evidently possess a high metabolic 

 rate produce an apical hydranth and a stolon at the 

 basal end (Fig. 64), but before it attains any great 



' I have described and discussed these facts in the following papers: 

 Child, "An Analysis of Form Regulation in Tubularia. I," Archiv fur 

 Entwickelungsmechanik, XXIII, 1907; IV and V, ibid., XXIV, 1907; 

 "Die physiologische Isolation von Teilen des Organismus," Vortrage 

 und Aufsdtze Uber Entwickelungsmechanik, H, XI, 191 1, 96-119. The 

 discovery since these papers were written of the existence of metabolic 

 gradients and their relation to physiological dominance affords a definite 

 basis for most of the earlier conclusions and interpretations. 



