(64) 

 a aorsal mesenter-y (no oti.er invests jrato r has seen this) and 

 in the trunk only a ventral mss enter/, 



V/hile it is fcssible ti:at the rucsocierii! arises as aivt^rtic- 

 ula from the enteron, as Caldv/cll and Masterman have described, 

 yet Lon.;chaHii.s , (12), v/ho nas recently re iiives tii^atea ti.e early 

 embryoloi:y of the f o rai t/it,^ CctidAell v<c>"Ked on, (Phoronia Kow- 

 alovskii ) aeiiiLies the orit,in of the cavity in front o -f* t r.c col- 

 lar triink mesentery from enteric aiverticulu. Ikca-j, (9), vvho 

 rocot,:niiies the "anterior uiverticula" of Caldwell in ti.o Japa- 

 nese species, nevertheless holds tnat tne body cavities ao not 

 arise from anterior diverticula but are simply produced by mes- 

 oblast cells applying:, themselves to and forrriinr t!;e lining of 

 ti.e ectcblastic and entcblastic wall. 



In the sectiovi on the iresoderm I nave stated ti.at ix^ the 

 embryo of Pkoronis architecta I do liO t find t^nat me mesouenn 

 arises from enteric diverticula. There cannot be the least 

 doubt, ho-.vever, that the preoral lobe at aii early s ta^e becomes 

 lined by a sac o "^ mesoderm cells ana that tuo wall o ''' tnis sac 

 i^i ves rise to t iie mesentery. T^rthermore , tr^is sac is extended 

 postero-laterally into two horns v/hich are characteristic of 

 tne cavity o^ the preorul lobe, according to Mastenran, Ikeda 

 and Mencn, It must be admitted, however, tjiat this sac does 

 not seem to retrain itb caracter as a sac but tuat the cells 



