JOURNAL OF ENTOMOLOGY AND ZOOLOGY 91 
It communicates with the main body cavity at a point on either 
side just anterior to the rhinophores (G@), and with the pedal 
sinus complex at numerous points (H), the main ones being at 
the head and tail, and just anterior and posterior to the opening 
into the auricle. It also gives off many short and long branches, 
above and below, as well as branches to the papille. 
The aeration of this blood is undoubtedly accomplished 
through the skin of the back and sides, to which branches of the 
sinuses are closely applied and through the papilla, which seem 
especially adapted for this purpose. The sinuses in the papille 
are much dilated at the ends, and communicate by many fine 
branches with the spongy network of which the substance of the 
papillew is composed, so that the blood is brought in close contact 
with the epithelium covering the surface. Also, when the animal 
is alive, the papille are in constant slow motion, which would 
facilitate aeration of the blood. 
The lateral sinus opens directly into the auricle by short 
branches, and the blood is then immediately returned into circu- 
lation without passing through the branchiew. The blood from 
the posterior aorta follows a different course from the rest. 
After passing through a complex mass of sinuses between the 
liver lobes, it is collected in venous channels that come together 
in a great sinus running along just above the stomach, from 
which it is carried to the branchie by the hepatic vein (A). This 
gives a single vein to each branchial plume. These run up the 
posterior side of the main trunk of the plumes and send off 
branches which, running forward close under the epithelium, 
are collected in veins (C) which run down the anterior trunk 
of each plume. These veins are collected into a single one which 
opens almost immediately into the auricle, thus returning the 
branchial blood to the circulation, where it is mixed with blood 
from the lateral sinuses. 
The branchie usually consist of three plumes, but there may 
be five, the number which MacFarland has described as typical. 
These have a muscular central stalk with several branches, which 
rebranch into fine ultimate endings. Each branchial plume 
receives a large nerve from the branchial plexus, and a branch 
