(63) 



adult, ^'or as iieiion (17) lias correctly observoa, Ui i s structure 

 id not i resent in the very youn^ Phoronis. However, ti.e epis- 

 toirie, '.vhich is of ectoaennal orit,in, soon makes its apt earanco 

 and v;hen the creature lias 30 tentacles, it is a verj conspicuous 

 organ. ("Pit:. 57) 



Ganglion:- The ganglion on the aortal surface of the hood 

 is lost when the precrai lobe is swallowed and hence does not 

 give rise to the so-called brain ganglion of the adult, 



Ectoden.-ial V/all of Collar;- Althougl; tne preoral lobe 



degenerateb, tne wall o -^^ the collar does not but beccmo^ drav.Ti 

 :ij.side the body v/ J' t ne yotini^ Phoronis aiiU tcirir, the ..^11 of the 

 oral end of the gut, 



Pe rianal Ciliated Rin^^ ana Ectodermal Wall of the Trirnk: - Wi lo n 



!.'^ critical point in the ?rie taruo rpiiosi s is reaclTed, tnat is, when 

 tne posterior end becomos dravai up to the region of the mouth, 

 tl:e perianal ciliated ring is i;sually seen as a pre tube ranee 

 in that region (Wilson's 'F'ig.lg) but shortly after this it be- 

 comes dra'.rn iii ;;aid tOt^ethor witn some of the ectoderm becomes the 

 lining of that part of the rectum -which is near t!;e anal opening, 

 (Fig.;j£) Tile drav/in^ in takes place to such an extent that most 

 of t}:e ectodermal wall of the trunk of tiie Acti no t rociia becomes 

 incorpor^teu in tho wall of ti.o rectum, as Caldwell has observed. 



This process-^ together wi t!i the drawing in o^ the ectodermal 



