CIRCULATORY APPARATUS OF THE NEMERTEA. 25 
and the lower brain-commissure become visible laterally and 
ventrally. By a more accurate contemplation with objectives 
of higher power, it can, however, be demonstrated that 
the circular muscular layer, which now consists of only a very 
few fibres, passes through the brain-ring at the same time 
with the lacunze and the proboscidian sheath, whilst the 
number of longitudinal fibres has increased remarkably ; and 
this circular muscular layer is the same which, behind the 
ganglia, will enclose the cesophagus, and thus is the same as the 
circular muscular layer of the body wall. The longitudinal 
fibres will form the layer of longitudinal muscular fibres, so 
that the circular layer which surrounds the lacune in the head 
of Carinoma is in no case comparable with the transverse 
fibrillar layer which surrounds the lacune in the head and 
other blood-spaces in Carinella. In the lacune of Cari- 
noma, however, I have found the same hyaline basal layer 
and the same epithelium cells as in Carinella. 
Immediately behind the ganglia the lacune grow down- 
wards, but both are divided by a common horizontal band of 
transverse muscular fibres. The upper lacuna is the larger, 
and lies on the side of the proboscidian sheath, slanting down- 
wards. The lower, or smaller, lies beneath the proboscidian 
sheath, and both of them between the two brain-masses. The 
broad band that separates the upper lacune from the lower 
consists of muscular fibres, which run from the left to the 
right, these fibres passing amongst those of the circular 
muscular layers. The two lower lacune are separated by a 
broad vertical band of hyaline basal tissue, in which numerous 
vertical transverse muscular fibres are visible, in the upper 
portion passing into the horizontal band, and in the lower 
diverging into the third (outermost) layer of isolated muscular 
longitudinal bundles, which layer penetrates here more inwards 
than elsewhere. The horizontal band disappears soon, thus the 
four lacunz again become only two, lying on each side of the 
proboscidian sheath. The mouth becomes visible, and presses 
the lacune still further from one another and upwards. 
The two lacune now extend dorsally (figs. 31 and 58), and 
