36 A. ©. OUDEMANS. 
uella, shows on transverse sections in its blood lacunze some- 
thing indefinite, and the lacunze sometimes go down very far 
beneath the intestine. Asto Valencinia, if we are in a region 
where the lacune have not yet wholly surrounded the ceso- 
sophagus, we are struck by the resemblance of the situation 
and habitus of the lacunze with those of Carinella. More- 
over, we are inclined to compare the arches of the lacunar 
spaces in Carinella, and the supra-proboscidian sheath-vessels 
in Carinoma with the proboscidian sheath lacune of Valen- 
cinia, for they are all separated portions of the blood-vessels, 
which have moved upwards, and are placed next to the probos- 
cidian sheath; and they are all in direct communication with 
the vascular system. The different situation which they seem 
to have in Carinoma and Valencinia may not be of im- 
portance. In Valencinia they lie within the longitudinal 
muscular layer, and in Carinoma they appear to lie in the 
longitudinal layer—but I say they appear, for, properly speak- 
ing, they lie also within this layer, but their high triangular 
shape makes it appear as if they were placed between the fibres 
of this layer. Further backwards they lose their triangular 
shape, descend to a lower place, and in habitus and situation 
more resemble the proboscidian sheath lacune of Valencinia. 
In Valencinia the intestine is comparatively wrge, and the 
blood-vessels lie beneath it; in. ©urinoma the intestine 1s 
comparatively small, and *’ne ‘nlood-vessels lie next to it. 
Let us now zumpare the two vessels in the proboscidian 
sheath i=. Carinella and Carinoma with the median dorsal 
vessel, of Valencinia. Suppose that the points of origin of 
{he two vessels in the two former are moved forwards, and at 
the same time approach the median line, and even reach this, 
so that they coalesce, then there is no reason that two 
proboscidian sheath-vessels will be formed. Only one will be 
formed, viz. a median dorsal vessel, lying in the median line, 
and at the bottom of the proboscidian sheath, and communi- 
cating with the two great lacune on the sides of the sheath, 
which now, in accordance with this simpler origin of the 
median vessel, will temporarily reach one another beneath the 
