314 
PROFESSOR E. RAY LANKESTER. 
iiig llie blood-stream when communication is once esta- 
blished and the brown granular wall becoming transparent 
and structureless by the absorption of its granules. 
Botryoidal tissue {so-called hepatic tissue ), — I have now 
to notice another development of the vaso-fibrous tissue, the 
characters of which are such as to confirm the view already 
advanced as to the potential identity of the brown-pigmented 
fibres and the vessels of the red vascular system. Nearly 
surrounding the wall of the alimentary canal, but separated 
from the epithelium of that organ by a vascular plexus, by 
a peculiar series of muscular fibres, and by fibres of the vaso- 
fibrous system, is a mass of dark-brown botryoidal tissue 
(PI. XXVIII, fig. 15), which has been, on account of its 
position and colour, regarded as hepatic.'^ I was not a 
little surprised on studying the structure of this tissue by 
means of transverse sections and of teased preparations, to 
find that it has in no way the least structural resemblance to 
a hepatic gland, but is simply a plexus of hsematophorous 
vessels, the Avails of which are swollen in botryoidal fashion by 
the enlargement of the individual cells which constitute them. 
The cells which constitute the wall are a single series ; there 
is no external tunic and no internal endothelium. In those 
parts of the plexus where its special character is fully de- 
veloped every constituent cell is seen to have a hemispherical 
shape, standing out on the surface of the vessel (PI, 
XXVIII, fig. 19), and its substance is found to be densely 
charged with very fine brown-coloured granules. A clear 
nucleus can be detected in most of the cells. The lumen of 
the vessels bounded by these singular cells is larger than 
that of the average thin- walled haematophorous vessel, mea- 
suring of inch on an average. The vessels form a 
true network in the denser part of the plexus, but every- 
where csecal branches of the vessels are found, which appear 
to be buds, as it were, of the system, which are growing for- 
ward to form unions with other branches, and so extend the 
plexus ; near the boundary of the masses of botryoidal tissue 
very interesting preparations may be obtained, showing the 
connection between the botryoidal vessels Avith thickened 
cells to their Avails and the thin-Avalled vessels of the general 
haematophorous system. Such a preparation is draAvn in 
PI. XXVIII, fig. 18. The botryoidal vessels are seen as 
buds or branches carried by a thin-Avalled vessel. 
The nature of the granules contained in the cells of the 
botryoidal vessels I have not in any Avay determined, and I 
am altogether unable to suggest at present Avhat may be the 
significance of this portion of the vaso-fibrous system. It 
