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



281 



evidence for it. The main reason for the change is with little 

 doubt the transformation of the covered ectoderm cells progres- 

 sively toward the base of the stem. Such a view is supported, 

 first, by the close approximation of the edge of naked ectoderm 

 to the zone of frustules which remains at its original propor- 

 tional distance from the basal end; second, by the ready trans- 

 formation of covered ectoderm cells into the naked type during 

 the regeneration of the hydranth in the region of transition, a 



Fig. 27. Fig. 28. 



Fig. 27. Longitudinal section of polyp with five or six peripheral 



canals. X 42. 

 Fig. 28. Section to show transition between naked and covered ecto- 

 derm of body wall. X 460. 



fact which will be illustrated in the third paper of the present 

 series. 



2. Development of Axial Parenchyma. — The most profound 

 change accompanying the transformation of the larva into the 

 adult is to be observed in the establishment of the axial rod of 

 turgid endoderm cells and the appearance of the peripheral 

 canals. It is accompanied by the development of a fenestrated 



