CONNECTIVE AND VASIFACTIVE TISSUES OF LEECH. 313 
red fluid is still present^ in the other the action of reagents 
had caused its removal^ leaving only the corpuscles. 
Connection hetioeen the hroicn fibres and the thm~walled 
vessels. — Here and there a careful search in longitudinal 
sections of the Leech (hardened in chromic acid^ per cent., 
followed by alcohol) revealed some thin -walled vessels 
(filled with their red fluid), in which the usual structureless 
character of the w'all w^as modified. Instead of being abso- 
lutely structureless the membranous wall showed thick- 
enings, which were densely packed with fine brown granules, 
identical with those of the brown fibrous tissue. After 
some search I found several examples of the direct continuity 
of thin-walled vessels with the tubular fibres of the brown- 
pigmented, system of fibres. Three such instances are repre- 
sented in PI. XXVII, figs. 8, 10, and 11. Figs. 9 and 12 
represent csecal terminations of branches of the red vascular 
system, in which it appears that the csecal extremity of the 
branch is continued into a fine fibre. Such an appearance 
admits of the interpretation that a prse-formed tube has 
been placed in communication with the red vascular system, 
wLich has then filled it wfith hsemoglobinous fluid up to the 
point where its lumen ceased, and where the tube ceases to 
be tubular and is merely a solid fibre. 
From these observations I cannot doubt that the thin- 
walled blood-vessels and the brown-pigmented fibres of the 
medicinal Leech are virtually one and the same tissue, pass- 
ing into one another by insensible gradation, and, what is 
of more importance, actually in continuity with one another 
at certain points, as processes of one and the same set of 
vaso-fibrous cords. 
It is not possible at present to oflfer a definite opinion as 
to whether the development of tubular portions of the brown- 
pigmented system of fibres into thin-w^alled vessels is a pro- 
cess which is always and normally going on in the LeeclFs 
body. It is possible to suppose that the solid browm fibres, 
the tubular browm fibres, and the thin-walled haematophorous 
vessels, are three permanent varieties of the vaso-fibrous 
tissue. But I am inclined to think from the fact that not 
even young haematophorous vessels with nuclei in their w’alls 
are to be met with in the Leech, and from the fact that the 
tubular browui fibres discharge into their tubular cavity 
nuiueious nuclei identical in appearance with the corpuscles 
which are here and there to be detected in the haemato- 
phorous vessels, that there is actually a continual develop- 
ment of offshoots of the brown-pigmented system of fibres 
into thin-walled haematophorous vessels, the nuclei enter- 
