(lo) 



tlie blastopore becor^es oval in shape ana an incti cation of a 

 veiitral furrow, first observea by Cald'.vell and callea a "prim- 

 itive groove", appears. In Phoronia arciiitecta t ni a groove 

 is only to be seen in one or two sections t^ack o "^ tn e blasto- 

 pore aftet" which tne ventral surface is convex. ( Fij^s . 18 (a) - 

 20(c) ) I was unable to make cut a "primitive st^-eak" as de- 

 scribed by Caldv,cll. (oa) The irastm.la v.-iiich is at first cir- 

 cular in horizontal section becomes slightly eloiitjatea vrhen 

 the blastopore takes on an oval shape. 



Gradually ti." blastopore lips close up r£,c "-e ii^t'^'-io rly 

 until tne blastopore becomes cii^cular in outline but much smal- 

 ler tiiaii it was rij_.,;inally. At the same time tne anterior 

 end of tl.e larva bej^ins to bend in a ventral direction aiiu the 

 archenteron become o clonic ated posteriorly. (Pi^j.^O) 



llo'.v ti-ie larva inc ""eases slit,ntly in lexu^ii: (''^i;^. 21) , the 

 blastopore assumes the fo nn of a transverse sxit, tliO anterior 

 eiid bends -farther veiitrally and the posterior end o'^' the ente- 

 ron becomes aj-i-lied to the ectoderm at the posterior end of 

 tne larva. (Fi^.21) 



lly observations en Pr:orcnis architects ag^eo with the de- 

 scription of Masterman (16), Ikeda (9) una Lon^caamps {12) in 

 rej^ara to the closure of ti;e lips of the blastopore and the re- 

 sultint; chan^^e in the shiaje 0-^ the lattery but I do not think 



