VASCULAR SYSTEM OF PHERETIMA 388 
diastole and systole of the dorsal vessel projecting imwards 
when the dorsal vessel is filling and the blood is coming in 
through both the dorso-intestinals and the commissurals, and 
lying flush with the wall with the apertures closed when the 
dorsal vessel contracts. 
Bourne (2, p. 334) says, ‘In Moniligaster asin Mega- 
scolex, while there are valves which would mechanically 
Fic, 7. Fie. 8. Fia. 10. 
Text-Fig. 7.—Portion of the dorsal vessel cut open along its median 
dorsal line showing the valves in its lumen. v.=the valves at the 
intersegmental septa ; v’.=valves at the entrance of the dorso- 
intestinals into the dorsal; »”.=valves at the entrance of the 
commissural vessels into the dorsal. 
Text-Fig. 8.—Section of the dorsal vessel passing through the region 
where the dorso-intestinals enter the dorsal vessel showing the 
valves at the entrance. d.v.=dorsal vessel; d?.v.=dorso-intestinal 
vessel. 
Text-Fig. 9.—Section of the dorsal vessel showing the valves at the 
entrance of the commissural vessels into the dorsal. d.v.= dorsal 
vessel ; comm.v.=commissural vessel. 
Text-Fig. 10.—Three sections of the dorsal vessel showing the inter- 
segmental valves, a.=about the place of origin of the valve ; 
b.=a little in front ; c.=still further forward. 
prevent blood flowing into the dorso-intestinal vessel from the 
dorsal vessel, there are no such valves where the dorso- 
tegumentary vessels join the dorsal vessel. I have, however, 
observedin Moniligaster and some other worms a sphincter 
muscle in the wall of the dorso-tegumentary vessel close to its 
