(14) 

 toderm are at thn apical ^ole in the talastula ana thoy bear lon^ 

 ;ilia but as £astn)lation takers place ana as tiio embryo elongates, 

 the thickening comes to occi:p:' '^ position nearer the anterior 

 end of the larva. (Fi^js. 15-15 ( a) -15 (b) ) As far as 1 am able 

 10 JudGC froni what nas been v/ritten, the ganglion makes its ap- 

 pearance much earlier ir. Phoronis architecta t nan in other spe- 

 cies, althouH- ?ioule (20) fi^'-res the "plaque cephalique" at a 

 rather early sta^e in Phcrcnio Sabatieri. The chan^-es which 

 take place in tiie shape of the blastopore are mucn like those 

 described by other investi^^ato rs. At the bej^innin-^ of ^^astru- 

 lation tr.e blastopore is wide open and circular in outline. 

 The lateral lips of the blastopore then t^radually d.-av/ togetl;- 

 er in tne posterior re[.:ion encloaini^ that part, of the wall of 

 the archenteron between tncm (Fi^;. 20(c) ) which becomes a solid 

 mass of colls continuous with tj.e colls of tr.e fiisod lips of 

 the blastopore. ( figs. ie(d) -lb(e) ) The cells of tne solia 

 mass are of the saiiiC character as those o"^ t>.e wall c/-^ the ar- 

 chenteron where th.e blastopore is open. They are quite gran- 

 ular except at the periphery where they project into tae cavity 

 of tne blastocoel aiid tneir nuclei are quite indistinct. Both 

 of these facts are cnaracteri stic of tne cells making up the 

 archenteric wall. ("Pi^. 16(c) ) 



As a result of the closing up of ti.e ulasto^ore posteriorly 



