BIOLOGICAL STUDIES ON CORYMORPHA. 30 1 



With the exception of the third, these are conditions that 

 govern tin- development . whether cnil i \ nuiic or regenerutixv and 

 they are ju-t tin- . < .millions by whose manipulation the original 

 pol.irity of the column can be reversed. Since such rever-al 

 depend- upon .in a< <-leration of proximal relative to di-tal de\el- 

 Opment, it WOUld seem reasonable to -u-pect that a local accelera- 

 tion in the development of the embryo might be the efficient 

 cause of ihc initial polarity in the individual. 



S : h a local growth area appear- in the embr\ o at the point 

 which hr-t lea\e- iln- e^g case and thereupon define- the oral 

 cxtremitN. 1 Thi- eMremity may emerge at any point not ad- 

 herent to the -iil.-iratum; \\hich qualiti.at ion indicate- that c..n- 

 limit- to -.-i<lerablt the an-a in which the oral 



pole inu-t appear. Since i\]< rtain barrier to the 



diffusion of oxygen into the egg if i- po--ible that \ariation in it- 

 thii kne-- ina\ be an important lactor in determining the po-iiion 

 o| i he oi.il p. .|e in ihi- ai- 



i. \i I \in.k \ i- 



!:.:: IV. 



