22 A. OC. OUDEMANS. 
of the body, remain beneath the level of the nerve trunks, and 
finally communicate in the tail. 
In the tip of the snout, already in the third section, where 
the thickness of the sections is about ~; mm., the communi- 
cation of the lacune (fig. 28) is visible. A few sections 
further the spacious lacuna is already traversed by vertical 
bands, extremely thin, consisting of transverse muscular 
fibres, which again diverge amidst the tissue that surrounds 
the lacuna. In the thirteenth section the lumen of the pro- 
boscidian sheath penetrates between these lacune, and is situ- 
ated in the axial line, but with one of the lacune above it. 
The two lacunar spaces on the sides of the proboscidian sheath 
gradually lose their thin bands, whilst they become divided, 
each by a broad vertical band (fig. 29). The lacuna above the 
proboscidian sheath becomes gradually flatter (seen in trans- 
verse sections, not marked in fig. 29), and is at every moment, 
sometimes to the left sometimes to the right, in connection 
with the lacunz on the sides of the proboscidian sheath, 
sometimes even with both of them at once. In the meantime 
a thick, circular, muscular layer is formed, surrounding all the 
lacunze, the contractions of which may aid in driving the fluid 
backwards. The circular muscular layer is closed entirely, 
and not, as asserts McIntosh, half open on its sides. Within 
this circular layer longitudinal fibres become visible, as well 
lining the four lacune as further backwards, between the 
fibres of the transverse bands which separate them. In this 
species, too, the fibres are not directly bathed by the fluid. 
Here and there the epithelium was visible very distinctly ; it 
has the same character as that of the foregoing species, con- 
sisting of little round cells with relatively large nuclei. A 
little before the brain-ring the two lacune on each side of the 
proboscidian sheath coalesce into one, so that when they 
pass through the brain-ring only one great lacuna lies on 
each side of the proboscidian sheath. Just before the upper 
brain - commissure the broad band of circular muscular 
fibres diminishes so suddenly that one is inclined to think 
it disappears there. The same is seen when the brain-masses 
