— 119 — 
to imperfect staining. As above mentioned, these membranes also 
envelope the processes issuing from the cells. 
The Åscidians. 
The pr otoplasm of the ganglion cells of the Åscidians 
has, in isolated, macerated preparations, a reticular appearance (vide 
fig. 55 — 56), quite similar to what is before described in MoUusca] 
Ltimhricus etc, and which appearance is, I siippose, to a certain 
extent, produced by primitive tubes, which in a compHcated way 
are woven between each other and are, in the preparations, partly 
seen in optic diameter. It is remarkable that a concentric arrange 
ment in the protoplasm round the nucleus can, only very seldom, be 
traced out. The shape of a great many cells, and the situation of 
the nuclei is, perhaps, to some extent, the cause of this. In sections, 
the protoplasm of the cells exhibits a reticulation similar to what is 
observed in isolated cells. At the points where the walls of the 
small meshes unite, small thickenings or granules occur, giving the 
protoplasm a slightly granular appearance. 
I have never observed in or outside the ganglion cells of the 
Åscidians, yellow granules, similar to those just described in the 
ganglion cells of Patella, neither in macerated preparations nor in 
sections. 
In sections of some large cells, I have observed a tendency to 
dififerentiation into small lighter stained areas, similar to what is de- 
scribed in the ganglion cells of Homarus. This differentiation is 
not, however, very prominent (vide fig. 58, a). 
In preparations treated with osmic acid, or fluids containing this 
agent, the whole protoplasm of the ganglion cells is also very 
deeply stained by carmine colours (picro-carmine). This indicates 
perhaps the presence of a special substance (compare what is said 
of this above.) 
The nuclei of the ganglion cells have a distinct thin mem- 
brane, and an inner structure which has a varying appearance, similar 
to what is above mentioned in respect of the ganglion cells of 
Homarus etc. A distinct nucleolus is generally seen. The nuclei 
are relatively large; they are situated in the mesial parts of the cells. 
A method which in my experience is very good for the nervous system 
of the Åscidians, is treating with osmic acid — i for \ — I hour, or even 
longer, then sufficient washing in running water and staining in good picro- 
carmine (i 'Vo) fo'^ 24 hours or longer. 
