— 88 — 
out is, as we have seen, the „primitive tube"; that is the thread o 
which the whole rope is woven. 
In transverse sections of some nerve-tubes, largish vacuoli or, 
as it were, primitive tubes, can be seen (fig. 5, f, f\ f^^; fig. 2, d). 
These vacuoli often occur in a peripheral layer just inside the 
sheath of the nerve-tubes (fig. 5, t\ f^). I suppose, hovvever, this 
appearance to be to a great extent artificially produced. In some 
cases the whole contents of the nerve-tubes has the same appearance 
5' ^1) 3.nd looks as if it were principally constituted of large pri- 
mitive tubes, amongst which only some few primitive tubes of the 
common size are seen. I do not feel disposed to suppose this 
appearance to be only an artificial and postmortem product, though 
I cannot with certainty account for its nature at present. 
We have, hitherto, only mentioned nerve-tubes of a relatively 
large diameter; these are especially numerous in the longitudinal and 
oesophageal commissures, as will be seen from fig. i, which re- 
presents a transverse section of an oesophageal commissure. We 
find, there, transsected nerve-tubes of very varying diameter.^) In a 
great mawy large tubes (t, f, ti) a deeply stained axis is visible; in 
other large tubes {t^') no axis is visible, n.t represent somewhat 
smaller nerve-tubes running in a thick bundle along the centre of 
the commissure. s.nt represent very small nerve-tubes situated more 
peripherically. 
Large nerve-tubes, usually having an axis, occur very frequently 
also in the peripheral nerves, vide fig. 7, t; they have generally, as 
will be seen, very stout sheaths, and are prominent. 
On the other hand there are, especially in the peripheral nerves, 
a great multitude of extremely slender nerve-tubes; indeed, the 
peripheral nerves principally consist of such nerve-tubes (fig. 7, nt). 
These nerve-tubes have so small a diameter that, I have, usually, 
only observed some few primitive tubes inside their sheaths (vide 
fig. 8, nt); in a large number of them I have even detected no pri- 
mitive tubes, and I believe they are partly constructed of only one 
primitive tube, the sheath of which is, however, much stouter than 
the spongioplasmic sheaths inside the larger nerve-tubes. 2) 
These slender nerve-tubes are, in most nerves, usually arranged 
or united in bundles, and are enclosed in neurilem-sheaths, larger 
fagots of these primitive bundles are again enclosed in larger and 
') We can find nerve-tubes with a diameter of more than 0.140 Mm. ; and 
we can find nerve-tubes with a diameters of less than 0.003 Mm. 
-) The diameter of these smallest nerve-tubes measures about .0017 Mm. 
