PROCEEDINGS OF SOCIETIES. 303 
favour of the view that such complete circuits may exist, 
while the fact that the fibres connected with many cells have 
been seen to proceed in opposite directions some distance 
after leaving the cell, is a very strong argument in favour of 
such general inference, and at the same time an explanation 
of many arrangements which are observed constantly in 
connection with nerve-fibres in various tissues. 
Many observers have described apolar and unipolar cells 
in ganglia in different parts of the frog. The author, on the 
other hand, has failed to discover any apolar or unipolar cells 
in this or in any other animal, and considers that the apparent 
absence of fibres, and the presence of one fibre only in con- 
nection with a cell, result from the defective modes of 
preparation generally employed. He maintains that every 
nerve-cell, central or peripheral, has at least two fibres 
proceeding from it.* In many cases he has demonstrated 
that these fibres pursue opposite directions, and he considers 
that such an arrangement is general, and therefore necessary. 
The author considers himself justified in drawing the follow- 
ing conclusions from observations he has made during the 
last three years : 
Ist. That in all cases nerve-fibres are in bodily connection 
with the cell or cells which influence them, and this from the 
earliest period of their formation. 
2nd. That there are no apolar cells, and no unipolar cells, 
in any part of any nervous system. 
3rd. That every nerve-cell, central or peripheral, has at 
least two fibres im connection with it. 
Though the present inquiry is limited to the structure of 
the particular cells connected with the ganglia in different 
parts of the frog, the author has studied the arrangement of 
nerve-cells and nerve-fibres in nervous centres, as well as at 
their peripheral distribution, in many different animals. 
* The word “cell” is only used in a general sense, as being shorter and 
more convenient than ‘‘ elementary part.” It consists merely of, lst, mat- 
ter in a living, active state (germinal matter), and 2nd, matter resulting from 
changes occurring in this (formed material). In Pl. XIII, what is ordi- 
narily termed “nucleus” and “nucleolus” of the nerve-fibre consists of 
germinal or living matter, while the matter at the lower part of the cell and 
the nerve-fibres are formed material. A nerve-fibre cannot produce a new 
nerve-fibre, but the “nucleus” or germinal matter of a nerve-fibre can pro- 
duce new nerve-fibre. The formed matter never produces matter like itself. 
Germinal matter can produce matter like itself, and from this formed mate- 
rial may result. 
