— 120 — 
or also sometimes near the pole from which the nervous process 
issues or in the opposite side. 
The pr 0 cesses of the ganglion cells. — The most common 
shape of the ganglion cells is the unipolar one ; the large, peripheric- 
ally situated cells, especially, are of this shape (fig.s 55, 56, 58). In 
the inner layers and in the dotted substance, cells with bipolar, tri- 
polar or multipolar shape occur (fig. 57). Each cell has only one 
nervous process, the other processes are protoplasmic, and their 
function is of nutritive nature. That is also, in my opinion, the 
reason wh}^ they principally occur in connection with cells situated 
in the inner layers, and are directed towards the external sheath 
(perineiirhm) enveloping the brain. 
The nervous processes exhibit a longitudinal striation, and their 
contents consist of primitive tubes. They are, in macerated prepra- 
tions, only lightly stained, and have an appearance different from that 
of the protoplasm of the cells. The protoplasmic processes resemble, 
in their appearance, the protoplasm of the cells. 
The neuroglia-membr anes enveloping the g angli on 
cells are very thin and but slightly prominent. The neuroglia is 
but little developed, and occurs very sparingly between the gang- 
lion cells in the brain of the Ascidians. 
Su mmar y. 
If the reader has follov/ed me in these researches on the struc- 
ture of the ganglion cells of various types of invertebrates, he will 
have gathered that there are some principal features in the structure 
which seem to be common to all the types investigated ; and, if it is so, 
we may conclude as above, in respect of the structure of the nerve- 
tubes, that those features in the structure of the ganglion cells are 
common to all invertebrated bilaterates. We may thus give the 
following summary of our results: 
1) The ganglion cells of all invertebrated bilaterates consist of 
a nucleus with distinct membrane, and a varying inner structure, and 
also of a. protoplasm with various constituents ; the cells are enclosed 
by a membrane of neuroglia-substance. 
2) The principal constituents of the protoplasm 3iVC primitive tubes, 
having the same structure as those in the nerve-tubes (they contain 
hyaloplasm enclosed in spongioplasm). The course, and origin (or 
termination) in the cell, of these primitive tubes I am not in a posi- 
tion to describe particularly ; some of them very frequently circulate 
