ON ANNELIDA. 
69 
plicated the anterior part of the venous trunk, or of its two 
branches, like a V. In the species in which the gills are 
dorsal, and on a great number of rings, the veins which re- 
turn from them, belong to the corresponding transverse 
branches. 
From the anterior extremity also of the bifurcation of the 
medio-ventral vein, spring the principal branches of commu- 
nication with the arterial system. These branches, placed on 
the sides of the oesophagus, ascend towards the back, and 
end at the dorsal vessel. 
The arterial system is formed by a thick medio-dorsal, or 
rather intestinal vessel, evidently swollen from ring to ring, 
at least in its action, by the blood which it contains, and 
furnishing on the right and left, some transverse vessels, 
which, when arrived at the root of each appendage, divide 
into two branches: one which proceeds forward, and the 
other behind. Each of these branches is itself divided into 
two branches ; one which returns internally for the hepatic 
lobes, and the ovaries ; the other which goes to the branchial 
part of the appendage. This, at least, is sufficiently observ- 
able on some nereides in the living state. 
With respect to the species, whose gills are at the cephalic 
rings, and much more complex, it is easy to see that the 
lateral branches of the dorsal vessel, must be much thicker, 
and that they are continued in the branchial cirrus, and in its 
ramifications. 
In the lurabrici, the thick dorsal vessel, with its pulsations 
and its lateral transverse trunks at each ring, are equally ob- 
servable, but without the branchial ramifications. There 
have been merely remarked, in front, two vessels, occupying 
towards the end the medial line ; one straight awlsmaller ; the 
other flexuous and of a more considerable calibre, neither one 
nor the other having pulsation. 
The apparatus of generation in the chetopoda has not yet 
