(16) 



tnat in Phoroiiis arciiitocta ti;e aefinitiv^ blastoporf^ is jusnea 

 fartr.cr- ^i.terior-ly b;- ti.o special activity iu ts^e posterior re- 

 gion of tne blastopore as Ikecia has fomi6 to bo the case for 

 Phororiio IJ irriai . I consider the aefinitive blastopore to be 

 represeiiteu by tic anterior part q-^ the wide circular blasto- 

 pore of the yoTni(_, i^astnjla. The chan£o in position of tne 

 blastopore with reference to the anterior end is a';.e to an 

 elont:ation of i-tie posterior portion of tne enibryo and the ven- 

 tral flexure of its Ulterior eiiU. 



My studies on the aevelopmevit o"!^ Phoronis architecta 

 lead me to aj-jree v.'ith Ike da ana Lontichamps as to the fate of 

 the cells in the posterior part of the blastopore and as to 

 the eotoderrrxal orii^in of the "posterior pit". The cells of 

 the posterior part of the blastopore become invae,iiiated by the 

 closure of the blastopore lips and fo na part of the ventral 

 v/all of the enteron, wi:ile the "posterior pit", whicii appears 

 in Phoronis architecta sliortly before the de^^initive blasto- 

 pore is fonned, is of ectodermal orij-in and has no apparent re- 

 lation to the ventral iV;roove. As Ikeda (9) has statea, the 

 pit is the bejjinnin-, of the nephridiuiii of the Actino t rocha. 

 In a recejit paper Masterman (16a) says that he has found tne 

 "posterior diverticulum" both in larvae of P. Buskii and P. 

 hippocrepia aiid tiiat he consiaers them to be the anla-^e of 

 the nephriaia. 



