1885.] The Relations of Mind and Matter. 685 
more and more widely separated, the fibril growing thicker and 
becoming a nerve fiber, with the power of conveying motor 
energy more rapidly and in greater quantity. Through some 
such process successive steps of evolution may have led to the 
condition now existing in the highest animals, with very numer- 
ous fibrils emanating from the cells, their combination into bun- 
dles with an insulating covering, and their final distribution to 
distant cells, 
For this idea we have a degree of embryological warrant, and 
can trace the nerve organism to one of its ancestral stages. For, 
as observed by Beale, the cells from which the nervous system 
arises form processes which connect adjacent cells together. They 
are thus direct counterparts of many, and perhaps of all, tissue 
cells. As growth goes on these cells separate, while their con- 
necting processes lengthen and form the axis cylinder of the 
nerve fiber. In this we seem to perceive the phylogenetic devel- 
opment of nerve tissue. Eventually, as some observers consider, 
one of these cells becomes a cell in a nerve ganglion, the other a 
peripheral end organ, their connecting process being lengthened 
out into a nerve fiber. That in this we have an exact representa- 
tion of the mode of development of nerve tissue, however, is far 
from certain. If so we should find each nerve fiber proceeding 
directly from one to the other extremity without intermediate 
ganglia. The frequent existence of these ganglia leads to another 
conclusion, and indicates that the original development pursued 
another line, which has been slurred over in the rapidity of unfold- 
ment like so many embryological characteristics. Various 
hypotheses of the mode of development of nerve tissue have 
been heretofore offered, the most notable being that of Herbert 
Spencer, but these are mainly philosophical. Still another may 
be offered which is in direct consonance with the recent discov- 
eries in cell and tissue formation above described, and which 
_ future embryological research may fully substantiate. 
The hypothesis which we propose is the following. We have 
seen some reason to believe that in single-celled animals the 
motor impressions received by the cilia or otherwise are distrib- 
uted throughout the cell by the fibrille. This distribution is at 
first general, but in case of special motions may become special, 
certain fibrillæ becoming specially capacitated, through exercise 
in this function, to convey the current. In Metazoan animals 
VOL. XIX.—NO. VII. 45 
