A NEW BRANCHIATE OLIGOCHATE. 333 
off the upper part of the ceelom from the lower part, and which 
corresponds to the ‘‘ waist ” of the figure of eight. There is 
nothing particularly noteworthy about the structure of the 
body-wall. The longitudinal muscular layer (/. m.) consists of 
a single layer of flat plates, the interstices between which are 
occupied by a granular nucleated substance which also forms a 
thickish layer on the inside of the muscles. Where the 
branchie arise the muscular layer is interrupted. The lower 
compartment of the ccelom is occupied, as already stated, by the 
nerve-cord and the blood-vessels. The ventral blood-vessel can 
be easily distinguished from the dorsal, not by its position, for 
they both lie side by side, but by the structure. The pulsating 
dorsal vessel has thicker muscular walls and much less blood 
in the lumen; the blood in this vessel was never so darkly 
stained by the carmine as the blood in the ventral vessel, I 
do not understand this unless it be that the muscular walls are 
particularly impermeable to that fluid. The dorsal vessel lies 
on the left side just above the nerve-cord, and when fully ex- 
panded is of about the same calibre as the ventral vessel. In 
parts, however, its lumen was so contracted that the vessel 
could only with difficulty be recognised, The ventral vessel 
has very thin walls, and was gorged with blood. It gives off 
(see fig. 13) a branch on the right side which immediately 
divides into two—a branch for each of the branchie. The 
branches run up and down the body close to the parietes and 
enter the branchiz: the efferent branch passes down the opposite 
side of the body-wall in a corresponding position, but I did not 
succeed in seeing its actual opening into the dorsal vessel— 
presuming always that such an opening exists ; but at the points 
where these vessels should open it always happened that the 
dorsal vessel was much contracted, while the end of the efferent 
branchial vessel was much dilated. This looks as if the flow 
of blood into the dorsal vessel was hindered at the moment of 
death by the contraction of the latter obliterating its lumen, 
and thus rendering the actual communication so slender as to 
escape attention, 
Another important point with regard to the circulatory organs 
