— no — 
many layers or membranes aranged concentrically round the contents 
of the process; only the innermost layer of these membranes can, 
however, be considered as the real sheath, What a great extension 
these structures can obtain is, for instance, seen in fig. 34, where 
pc is the contents of a nervous process, hr is a branchlet issuing 
from the process ; nm the surrounding concentrically arranged neu- 
roglia-membranes. 
The nervous pocesses are sometimes provided with similar con- 
centrically arranged sheaths quite from their origin in the ganglion 
celi (fig. 25, sh). Generally, the sheaths do not, however, reach 
their highest thickness before some distance from the cell, and they 
do not consist of so many layers near their origin. 
The nuclei of the ganglion cells are, as is a well-known 
fact, enclosed by a thin membrane. That this membrane is not 
seen in the live-state of the cell, as stated by Freud, is, in my 
opinion, from the same cause as makes the striation of the nerve- 
tubes so slightly visible in the live-state. The refractive difference 
between the protoplasm of the ganglion cell and the substance of 
which this membrane consists is so small, that this difference must 
necessarily be increased, for instance, by chemical agents, if the 
membrane should become distinctly visible (vide fig. 23). With hæ- 
matoxylin this membrane gives a distinct blackish staining (fig.s 37, 
38, 40, 42) which is quite similar to that of the spongioplasmic re- 
ticulation, and to the sheath of the cell. In my opinion, it is not 
improbable that this membrane is also formed by the same spongio- 
plasm as forms the reticulation in the protoplasm and the sheaths 
of the primitive tubes. 
The structure of the nuclei inside this membrane varies very much. 
As already stated by Freud, there appears within the nucleus a great 
many changes, probably connected with the life of the cell and the 
nucleus. In well fixed preparations we can, in fact, also find nuclei 
exhibiting the greatest variation in their structure. Fig. 41 and 42 
represent nuclei in various stages. Generally, each nucleus has one 
nucleolus situated in its centre or also near its membrane (cmfr. fig. 38). 
Sometimes two nuclei are present; the nucleus has, then very often, 
an oblong form, and one nucleolus is situated in each pole (fig. 37); 
it is, however, not unusual that the nucleus has a circular shape, and 
that nucleoU are situated oposite to each other, near the membrane 
(fig. 41). Sometimes no real nuclei are present, the whole nucleus 
exhibiting a peculiar distinct reticulation with dark thickenings in 
the points where the fibres of the reticulation unite (fig. 42, d). 
Sometime fibres are seen radiating from the centre of the nucleus, 
