70 

 FCFr'ATIOr CF 7HF FrDCDERi:. 



The forT.tior of the p-^dor'err- ir Turritorsis carrot 

 be -dsTted to any of the sche-es of the develo'i^cr.t of the 

 Hydro-edusae rhich have "beer sketched by '■etrchr.il'cff , 

 He dint irruishes three Tinciral rp+hcds for the develor-r 

 rent cf the inner rerr layer: First, delarination , a 

 rrccers: ir rhich the i^e.cfert^'np blastc-eres divide in a 

 plane nearly parallel to the rurface; and the inner rarts 

 or cells be'^ore -^ri-itive erdoderr^, vhile the outer rarts 

 rerain as rriritive ectoder-. Second, '-iilti'^'r^lar inpres- 

 sior, i-" "hich cells riprate i^to the blastoccele fro" dif- 

 ferent regions of the rerinheral cell layer, a-d ere trans- 

 ferred irtr e'doder^al tissue directlv. Of this '-ode he 

 describes seve-^al subordinate types. Third^ u'^inolar "i- 

 pration, similar to the '-■recedinp exce-nt that the ':ri'^i- 

 tive endoderr cells are piven off at one pole only; at 

 the 'posterior end oT the larva. 



In Tiirri-opsir the e'-dodern is derived fro-^ the syn- 



