
326 THE AMERICAN NATURALIST. [Vor. XXXVI. 
ends of parietals, Having branches to the nephridia as the 
parietals do. 
3. Connections of the laterals with the dorsal in somites X 
and XII, corresponding to the dorsal ends of parietals. 
4. Anastomoses between the parietals of somites XII, XIII, 
and XIV, in apparent continuation of the laterals. 
5. Presence of branches of laterals to the body wall along 
the septa, corresponding to respiratory branches of the 
parietals. 
6. Presence of branches to the seminal vesicles, which are 
also supplied by branches from the ventral. Here, as else- 
where, branches of the parietals take up blood which is brought 
from the ventral. The parietals are in the best position to 
supply the vesicles which are developed from the septa. 
The origin of the hearts and laterals and the position of the 
laterals within the circular hearts are problems which require 
more facts for their solution. An extended discussion of them 
is beyond the province of this paper, but one or two sugges- 
tions will be made. The suggestion of Harrington that the 
hearts are modified parietals is negatived by the presence of 
both parietals and hearts in somite X, and by the different 
ventral connections of the parietals and hearts. It seems 
more probable that the hearts are enlarged circular intestinal 
vessels, serving to carry the blood brought forward by the dorsal. 
The lateral vessels must have arisen as anastomoses between 
successive parietals serving to return the blood from the head 
(brought forward by both dorsal and ventral), to the dorsal 
behind the hearts. The dorsal connections of the parietals in 
front of the hearts have disappeared from disuse. The posi- 
tion of these anastomoses within the circular hearts seems to 
indicate that they, too, have been derived from the capillaries 
of the cesophageal wall, although later than the hearts. This 
suggestion would explain the branches of the lateral vessels to 
the cesophagus and hearts, which otherwise are unexplained. 
Conclusions. — The course of the circulation in each seg- 
ment behind the hearts is as follows: the branches of the 
lateral neurals and parietals collect blood from the body wall; 
the parietals take- blood to the dorsal from the subneural, body. 
