324 THE AMERICAN NATURALIST. [Vor. XXXVI. 
5. The Dorso-Intestinals. — When one clamp was put on the 
dorsal vessel and anumber of parietals were cut just in front of 
it, the dorsal vessel only partly emptied; but when the dorso- 
intestinals in the same segments were cut the dorsal vessel 
emptied entirely. This and the experiments on the parietals 
described above, in which the cutting of the ventro-intestinals 
in one case and of the dorso-intestinals in another resulted in 
the decrease of the dorsal vessel in those segments, show that 
the dorso-intestinals carry blood to the dorsal. 
6. Lhe Lateral Vessels.— When the laterals are clamped 
either at both their connections with the dorsal in somites X 
and XII or in front of the connection in X, they remain full 
of blood, sometimes much distended, in front of the clamps. 
No vessels have given more positive and unmistakable results 
than these. 
CRITICISM AND CONCLUSIONS. 
There is no difference of opinion in regard to the blood flow 
in any part of the dorsal vessel. All authors agree that it 
flows forward to the extreme anterior end of the worm. 
Bourne alone suggests that the blood flows forward from the 
hearts in the ventral vessel, since he considers that the strong 
contractions of the hearts would force blood forward as well 2s 
backward. Our experiments have confirmed this plausible 
view, and it may be regarded as proved that the blood flows 
forward in this part of the ventral. 
Although previous workers have not agreed upon the func- 
tions of the parietals and dorso-intestinals, they all agree in 
assigning to these vessels opposite functions. The above 
experiments on the parietals, although not wholly decisive, 
give strong support to a different conclusion, namely, that 
both parietals and dorso-intestinals carry blood to the dorsal. 
It follows necessarily that the ventro-intestinals supply the 
intestine with blood, as Bourne and Harrington contend, 
According to Harrington’s interpretation all of the blood in 
circulation would have to pass through the ventro-intestinals ; 
in other words, all of the blood which is carried forward by the 
dorsal and all that which passes downward from the dorsal in 
