CIRCULATORY APPARATUS OF THE NEMERTEA. 53 
forwards beneath the proboscidian sheath, and communicates 
indirectly with the lacune. For a few slices the great lacuna 
retains its horse-shoe shape. Then a horizontal band of trans- 
verse fibres divides the lacuna into three, two on the sides of 
the proboscidian sheath, and one beneath it. The lower 
brain-commissure is passed by, and the mouth becomes 
visible, and still the whole figure is the same. Now the 
two lacune next to the proboscidian sheath embrace the 
posterior lobes. The horizontal band is still present and also 
the lacuna beneath it. On the sides of this lacuna two others 
arise, which of course terminate blindly forwards. These three 
are separated by vertical muscular fibres, passing into those of 
the proboscidian sheath. So the area of the circular muscular 
coat is divided into two unequal parts by the horizontal band. 
The upper or larger and the lower or smaller are now divided 
by the same two vertical bands into three, so that there are 
three large and three small compartments. The central one of 
the larger is filled by the proboscidian sheath with the median 
vessel. The two larger on the sides are the lacunz with the two 
posterior lobes bathing in them, and the three smaller are 
flat lacune. [Each lacuna besides its own coating of epithe- 
lium and its hyaline basal layer, is surrounded by longitudinal 
muscular fibres. Now the middle one of the three smaller is 
pushed away by a mass of transverse and longitudinal mus- 
cular fibres which cause the lacuna to communicate with the 
two others next to it. (In my specimen, however, it opened 
‘nto the left one, but this seems to be abnormal.) So we here 
meet again the ordinary arrangement; two lacune, one on 
each side of the proboscidian sheath, separated by a horizontal 
band from two smaller beneath the sheath, which in their turn 
are separated by a vertical transverse band. The lower or 
smaller embrace the stomodeum. Here and there between its 
folds small lacune remain visible. In Cerebratulus urti- 
cans I already had an opportunity of remarking that several 
of these lacune terminate blindly backwards, at least they 
disappear. The same now is the case here behind the mouth, 
so that only a few sections further backwards there are no 
