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Vol. 3] Torrey. — Biological Studies on Corymorpha. 



269 



k 



separated from the epithelium of the hydranth cavity. What- 

 ever our assumptions regarding the few small deeply staining 

 cells in question, there is no doubt that they furnish several 

 cells to the axial endoderm of the tentacle, by a process which 

 would seem to come into the category of morphallactic phenomena. 

 An evagination of that area of the endoderm occupied by the 

 small cells accompanies their appearance. At first it produces 

 no external effect, for the layer of continuous ectoderm externa] 



b 



Fig. 16. Longitudinal section cut through a developing proximal ten- 

 tacle. X 910. 



to it thins out as it advances, apparently because it advances, 

 the endoderm leading the way. The ectoderm cells on either 

 side of the thin area next increase in number, forming a some- 

 what thickened ring about the growing tentacular axis. The 

 latter, carrying the thin layer of mesogloea with it, is pushed 

 out as a single column of cells from the endodermic evagination 

 (Fig. 16). 



A number of cells varying from four to ten are thus incor- 

 porated in the developing tentacle. The positions of the cells 



