CIRCULATORY APPARATUS OF THE NEMERTEA. 61 
They move just before the cerebrum, a little upwards, next 
to the proboscidian sheath, and whilst going with this through 
the cerebral ring, they protrude downwards between the sheath 
and the brain-masses. In the specimen I examined something 
abnormal took place. The left vessel did not reach the ventral 
surface of the sheath, the right one did; it was very much 
enlarged, and filled with blood-corpuscles (diastole ?) and com- 
municated with the vessel in the sheath. The vessels remain 
where they are, they do not go upwards, because the brain- 
masses move sideways and diminish, and the lower commissure 
disappears. The vessels go downwards but remain above the 
level of the lateral nerves. The median vessel left the sheath 
after twenty-four slices (I estimate them to be one thirtieth of a 
mm. Thebody hada widthof onemm.),andsome ten slices behind 
the lateral vessels move beneath the level of the lateral nerves. 
With regard to the nephridial system, it lies behind the 
ganglia. It consists of a very crooked canal above the lateral 
nerves. After twenty-five slices it disappeared, and thus it is 
very short. I did not see any communication with the vascular 
system. At the first appearance of the system on contemplating 
the slices from the front to the hind part, the two excretory 
ducts were very distinctly visible. Thus they are as much as 
possible in the front. Together with the whole system they 
are situated above the lateral nerves, but instead of running 
nearly horizontally towards the skin, they proceed almost 
vertically downwards, and so these ducts have ventral 
apertures. 
Neither of the vascular, nor of the nephridial systems, can I 
mention any histological particulars. 
16. Amphiporus hastatus, Mc.Int., figs. 8, 13, 
538, 63, 64, 70, 71. 
The mouth and the proboscidian sheath have again a common, 
almost terminal aperture. The proboscidian sheath falls into 
thestomodeum just before the lower brain commissure. Brain- 
respirators absent. 
I did not find a vascular loop in the head, nor the two vessels 
