552 



CKESSWELL SHEAKEK. 



TKa^la^s^^"^^- 



Text-figs. 7-12. 



PKysa- 



l.m,l 



Attv^- 



Iml 



"Imr 



IrrV 



Lrtm. 



Text-fi-s 7-;).-Gastrulatiou stages of Tlialasseuia (Tovrey)- 

 Text-fiU 10-12.-Physa (Wierzeiski). M.e. Ccelomesoblast. 

 I ml. Left portion of tl.e ectomesoblast. l.m.vi. Median portion 

 of same. Lm.r. Right portion of same. 



