CIRCULATORY APPARATUS OF THE NEMERTEA. 33 
soon as the cesophagus is inclosed by the circular layer, it is at 
the same time surrounded by the longitudinal muscular layer 
and the lacune (fig. 5]). The small transverse bands which 
continue to divide the lacune, are also present round the ceso- 
phagus and keep it connected with the circular layer, at an 
almost equal distance all round, of course not on its dorsal side 
where the proboscidian sheath lies, which is at the same time 
the cause, that on its sides through the whole length of the 
cesophageal region, a lacuna is visible, larger than the others. 
I shall call them proboscidian sheath lacune. 
I have carefully examined all the little transverse bands of a 
small portion of the oesophageal region, with respect to their 
width and situation, but did not find any indication of meta- 
merism or segmentation, so distinctly expressed behind the ceso- 
phageal region, both in the intestine as well as in the vascular 
system. 
In the specimen examined the lacunar or cesophageal region 
took up nearly one third of the whole length of the animal. 
The lacune in the hindmost part of this region become 
gradually larger, at the same time diminishing in number, 
especially ventrally. 
In this region, at the same time, a little more forwards the 
vessel in the proboscidian sheath penetrates through the wall 
of the sheath, and now lies below it, but so closely against it 
that I could not distinguish the two muscular layers, for the 
vessel too has now a very thin circular muscular layer. Also 
the intestine lies so closely against the blood-vessel that no 
space is seen between them. The process takes place within 
five slices, and it appears as if the circular layer of the 
proboscidian sheath moved upwards from below. 
The median vessel, when lying in the sheath, shows an inner 
epithelium layer of the same cells which everywhere limit 
blood-spaces ; then follows a hyaline basal layer. It always 
lay above the epithelium layer of the sheath, and the dorsal 
half of the wall of the vessel had quite another histological 
character than the ventral half. The layer outside the hyaline 
basal layer showed on the dorsal half glandular cells, as if the 
8 
