CIRCULATORY APPARATUS OF THE NEMERTEA. 31 
cinia it is placed still further backwards. In my specimen it 
becomes first visible in the fifty-sixth section, thus nearly on 
1 mm. from the tip of the snout (in the preserved specimen), 
goes upwards till it reaches the circular muscular layer, and 
penetrates this a few slices further backwards, finally remain- 
ing in the centre of this ring-shaped layer. When the pro- 
boscidian sheath first touches the circular muscular layer the 
number of the lacunze diminish by communicating with one 
another, and deviate more from the median line; but after the 
circular layer has given a passage to the sheath and has 
enclosed it, the number of the lacune is diminished to two, 
lying on the sides of the proboscidian sheath. There is no 
lacuna above the latter. One may thus say that in Valen- 
cinia the lacune in the head communicate not directly above 
the proboscidian sheath but indirectly. The brain-commis- 
sures now become visible, and the circular layer, the longitu- 
dinal fibres, the lacunz and the proboscidian sheath protrude, 
as in Carinoma, through the cerebral ring. The lower half 
of the cerebral ring being very thick is seen in many slices. 
In the hindmost three sections, where it was visible, the two 
lacunz slant downwards, and the fibres of the proboscidian 
sheath cut off a part of the left lacuna and enclose it between 
them. (Fig. 54, referring to Lineus sanguineus, may also 
serve for this species.) I believe this is abnormal, for in all 
Nemerteans where this process takes place, and which I 
examined also on transverse sections, both the lacune, except 
in two other cases, participated in this process. For the 
moment we leave the dorsal vessel in the proboscidian sheath, 
only pointing out that here as in Carinoma, a part of the 
lacunz as it were penetrates the muscular wall of the probos- 
cidian sheath, and extends further backwards as a vessel in 
the latter. This process I have also been able to follow in 
sagittal sections. 
The lacune again remove to the sides of the proboscidian 
sheath. Now, beneath the latter a lacuna becomes visible, 
which terminates blindly in front, and in a following section is 
broad and flattened and thus may be compared with the “‘infra- 
