{66) 



Tiiio conaitioii o ^^ affairs in the well develc:. ou Act iiio tro cha 

 d v.'iiat one would expect froiri trie dispositioii of the raeaoaorrrL 

 -dis in the vory youii-^ larvae o +' Pnoronis architecta where it 

 iy Ciily verj seldom trat any are foiuia en tn_ at^aach wall, 

 (Fit.:. 24) 



The absence o"?" a mesoaernial liniUj^ on tl;e splanchiiic wall 

 of tiie collar cavity is maae all tke more evi aont ty tr.e exami- 

 nation of cro3:j sections sho^vin^ ti=o colla.'' trunk mesentery, 

 (Fi|_^3. 51 ({:) -ol(it) ) Wi^ien tfie mesentery reacnes the stomach 

 wall, instead of dividing into tv/o layers one»o"*^ wfiieh \\ould be 

 continued into trie mesodermal linin.., of the atoniacii waxl of tlie 

 c^i.j.ar cavity, it turiio abruptly upon itself and becomes tke 

 lii;iri^ 0"^ the stomacn wall o "^ ti.e trunk. 



I have iiever founa the least iiidication in tke collar- cavity, 

 "l^ a dorsal mesentery such as I'asterman (15) has described in 

 the Ac ti no tro cha -from St. Andrews Bay, 



The trunk cavity is lined throut^hout by a sac o •*" mesodermal 

 epithelium and the mesenter:, is plainly seen to be continuous 

 with the lining of the somatic wall and wi tr. the linin^, of the 

 wall o f the gut. 



The ventral mesenter-y of the trunk is; preseait in Species, A. 

 and. Spe'cies, B, , and vrhile there is no aorsal mesei^tery, I /-.ave 

 found indications; of it in t to specimens only (Species, B. ) at 



