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 w^hich 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 lumbrici, 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 and smaller ; 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 



