894 
PEOFESSOE EE ALE ON THE DISTEIBIJTION OE NEEYES 
nucleus (Plate XLI. fig. 1, after Kuhne, figs. 2, 3 a, 5), it is possible, and indeed probable, 
that it is continued onwards for a greater distance than it has been followed in Kuhxe’s 
specimens. As a rule, it becomes too delicate and transparent to be traced further than 
has been represented in my drawings (figs. 14, 16, 18, 19) ; but I submit that the evidence 
adduced in favour of these ends being actual terminations of the nerve-fibres is very far 
from conclusive. Capillaries, when stretched and torn, give rise to a very similar appear- 
ance; and it is not uncommon to find an undoubted capillary vessel which gradually 
becomes fainter and fainter until every appearance of it is all hut lost, and this even when 
the tube remains quite perfect. I have proved this in the case of capillaries, distributed 
to muscle, which had been injected with prussian blue injection, and so stretched that the 
injection was removed from the tube for a certain distance. In this space the vessel could 
not be recognized, and all that could be seen was a faint granular appearance. We 
therefore cannot conclude that nerve-fibre or capillary ceases, merely because we cannot 
follow it in certain specimens beyond a certain point. It may exist but be quite invisible. 
2. In various tissues to which nerves are abundantly distributed, the appearance 
represented in fig. 3 « is common. This looks as if the fibre extended from the 
nucleus in opposite directions ; while the common appearance, represented in fig. 3 c, in 
which two fine fibres are seen running together, is strongly in favour of the view that very 
fine nerve-fibres run for a considerable distance beyond the point at which the dark- 
bordered fibre can be demonstrated, without terminating in ends. It will be observed 
that the fine fibres represented in my figures are not one-sixth of the diameter of 
Kuhne’ s terminal fibres ; and I have seen many fibres much finer than those represented 
in fig. 3. 
3. The finest nerve-fibres visible by the highest powers can often be proved to dinde 
into two fibres, by tracing them to the point where they pass into a fibre running at right 
angles (fig. 4: a a). 
4. I have some preparations of the bladder of the frog, in which very distinct networks 
composed of very fine nerve-fibres are readily seen. One of these, magnified by a power 
of 1700 diameters, is shown in fig. 6 . This, it might be remarked, is not completely 
conclusive in favour of nerves forming circuits ; for it is possible that fibres may diverge 
from the bundle with which they run and end in free extremities or in small cells, as 
represented in fig. 5. Numerous observations are against this view ; and I regard certain 
nuclei from which two or three fibres pass in different directions (figs. 2, 3, a, h) as the 
peripheral and active portion of the nerve-fibre in all cases. Even in the case of the finest 
fibres, when a nerve joins another branch running at right angles to it, fibres are given 
off" which pursue opposite directions (apparently pursuing opposite com'ses), towards 
the centre, and towards the periphery. 
5. With regard to the size of the finest nerve-fibres, I have traced fibres from time dark- 
bordered nerves which are certainly less than the 5 ^ 00 0 ^^ diameter, and 
these are probably composed of more than two fibres. Still finer fibres of this description 
have been traced to and from ganglion-cells. The connexion between such very fine 
