(90) 

 canal ana thus allov/s tne blooa corpuscles lo move abouo be- 

 :v.'eeu these tv.'o layers tnroUi^hout the extei.t of the a lime n tar y 

 caiicil. (■pic^.o9(a) 



The dorsal bloca vessel (" rued iaiice fas z" (Cori), "efferenr, 

 vessel", (Benham) ) and the rin^ vesel with its tentacular ves- 

 sel are corriplptely forrriea vessels at this stage. The aorsal 

 vessel is still freely ocen posteriorly iuto the space or sinus 

 betv/een the stomach wall aiid its inesoderrnal covering ana blooa 

 corpuscles eore carried back aria forth from the vessel to the 

 vinus by- the contraction ana expansion O"^ the f o rire r. Anter- 

 iorly the aorsal vessel can plainly be seen opening into the 

 rin^^ vessel, (larval collar cavity) 



The origin q-^ the connection between the dorsal vessel and 

 liie ring vessel and the man...er iii v:hich the blooa corpuscles 

 find their way into the dorsal vessel are queBtions whiich have 

 not been very satisfactorily elucidated, A.c t.ino tro c ha Species, 

 A., to my mind, presents no grp^t aif-fic'i^ti '^^ in tne way of 

 understanding how these processes take placp. The dorsal blooa 

 vessel opens posteriorly into the sac-like ainus arouna the loop 

 of the alimentar:,^ canal ajid it seems probable :rom an exa^nina- 

 tion 0+' sections o '' tie critiu^l stage that it is also open an- 

 teriorly. Assuming that such is the condition, it -.vill open 

 into the space betv/een t^ie mesoderrral lining and the '-=,11 of tiie 



