296 University of California rublications. [Zoology 



oi"' the frustiiles upon the latter in longitudinal series introduces 

 an inhibitory factor in the shape of the relatively unproductive 

 vacuolated cells occurring between the canals. 



The shift of the perisarc back along the stem at metamorphosis 

 may be interpreted as involving a transformation of cells in situ 

 from the covered to the naked variety. The origin of the gono- 

 some from the evagination of endoderm and ectoderm at the base 

 of the hydranth is only another indication of plasticity. 



Zoological Laboratory, 



University of California, 



Berkeley, March 28, 1906. 



