CIRCULATORY APPARATUS OF THE NEMERTBEA. 25 
rates the larger lumen from the neighbouring smaller one, 
passes upwards into the circular layer of the proboscidian 
sheath, and below it surrounds the esophagus. It thus proves 
to be the constrictor muscle of the cesophagus, and the smaller 
lumen lies within this constrictor, the same as I have seen 
in Carinella. 
On the right side I only saw a similar communication 
between the vessel in the proboscidian sheath and the lumen 
within the cesophageal constrictor faintly indicated; but a 
connection between this and the great lumen I have not seen. 
McIntosh says that the two vessels in the proboscidian sheath 
have no connection with the blood-vessels anywhere. It is 
thus probable that this connection disappears when the animal 
becomes older, or that it only appears when the animal has 
reached a certain age; this only is sure, I have seen the con- 
nection. These two vessels are not very long. In the speci- 
men I have examined, they are about one fifth of the cesophageal 
region. They terminated blindly, but not as in Carinella, 
gradually, but at once. Perhaps this is to be ascribed to the 
posterior end being filled with fluid or not. In regard to the 
histological structure, I cannot mention more than that they 
are invested on the inner side with the same layer of small 
cells as the blood-vessels and the proboscidian sheath; that their 
hyaline basal layer sometimes passes into that of the probos- 
cidian sheath, sometimes is separated from it by the same cells, 
and that the epithelium layer of the proboscidian sheath 
always covered the vessels on their outside. 
We now return to the region of the mouth, to the two great 
lacunze with which the four last mentioned vessels are con- 
nected. These two great lacune, seven slices further back- 
wards, are already surrounded by a circular layer of muscular 
fibres. This circular layer is well developed. A few slices 
further backwards the circular layer becomes thinner and 
thinner, but it still exists. Not before the midst of the 
cesophageal region some longitudinal fibres become visible 
outside of the circular, which are also not very sharply limited 
there. An immersion objective very soon showed that they 
