No. 424. ] THE BLOOD FLOW IN LUMBRICUS. 327 
wall, and nephridia; the dorso-intestinals give blood to the 
dorsal from the intestine ; all of this blood goes forward in the 
dorsal to the hearts; through them nearly all of it is given to 
the ventral vessel, which sends it to the intestine through the 
ventro-intestinals and to the body wall through the ventro- 
tegumentaries. | e | 
The head region is supplied with blood by the dorsal and 
ventral vessels, and the neurals and laterals carry blood 
from it. 
The dorsal and ventral vessels carry mixed blood, the dorsal 
receiving oxygenated blood from the parietals and non-oxygen- 
ated from the dorso-intestinals. The neurals carry oxygenated 
blood only. The dorsal and ventral vessels carry mixed blood 
to the head region; the laterals carry backward mixed blood, 
and the neurals oxygenated blood. 
There is no support given by our experiments to the idea of 
a more or less complete segmental circulation in Lumbricus. ` 
The circulation is strictly systematic, the blood making a com- 
plete circuit from the hearts backward through a greater or 
less number of somites, upward through the body wall, nephri- 
dia, or intestinal wall, to the dorsal, and thence forward to 
the hearts. This scheme of circulation is simple, and the 
slight modifications of it, which occur in the head region only, 
have received at least an attempt at explanation above. The 
interesting and highly important question presents itself : 
What happens when a worm's head is cut off and it lives 
and regenerates a new head, or perchance a tail? "With the 
removal of the hearts some substitute must be provided to 
carry the blood from the dorsal to the ventral vessel. A series 
of regeneration experiments have been begun to find the 
answer to this question. 
October 23, 1901. 
