MULTIPLE NEUROMATA OF THE CENTRAL NERVOUS SYSTEM. 783 
The possibility here also is that these are aberrant anterior nerve roots which in early 
foetal life have taken this aberrant course, and that later some influence has caused 
a proliferation of the sheath of Schwann cells at the growing tips of the fibres with 
the formation of nucleated tubes and fusiform cells: these would therefore retain their 
connection with the centre just as the new fibres in the stump-neuroma. This explana- 
tion, while satisfactory for the cord, from the point of view of the cell-chain structure 
of the nerves, prevents the unification of the processes, for there can be no such 
analogous explanation of the nucleated tubes and fusiform cells in the medulla and 
pons. If, now, in our endeavour to correlate the changes, we pass from our observa- 
tions to the conceptions which they justify, it is essential to admit that the question 
of the genesis of the nerve fibres is the same as the question of the genesis of the 
fusiform cells. 
Before entering upon the consideration of the origin and nature of the fusiform 
cells, it is necessary to ask what collateral evidence we have that such fusiform cells 
can thus form nerve fibres, and we find that along three pathways research has led 
to the conclusion that the peripheral nerve fibre arises as a multicellular structure. 
It is beyond the scope of this paper to deal with the general evidence for and 
against the different views relating to the development of the nerve fibre in the 
embryo, in regeneration, and in tumour formation, but from this evidence we wish to 
take such observations as throw light on our own. 
(a) In embryonal development.—The works of Batrour, Dourn, BEarp, HorrMay, 
and others have demonstrated that, in Elasmobranchs and Selachians, cells, migrated from 
the embryonic medullary tube, form cell-chains, and that each nerve fibre proceeds out 
of any single chain by a differentiation within the protoplasm. In the higher vertebrates 
the conditions seem not quite so simple. Numerous recent observations, especially 
those of Berns, have shown that the first evidence of nerves consists of a characteristic 
series of cells which form a syncytial cell-chain, and that the first fibres lie within the 
protoplasm of this syncytium. Kouv, too, in rabbits, has demonstrated the gradual trans- 
formation of the indifferent cells of the spinal ganglionic anlage into ganglion cells and 
nerve fibre cells, and the development of the latter into nucleated tubes, and finally 
into the fibres of the sensory nerves, the nuclei becoming ultimately the nuclei of the 
sheath of Schwann. Kouvn, further, has shown that the indifferent cells of the spinal 
ganglionic anlage migrate along developing nerve paths, e.g. the visceral branches 
of the spinal nerves, to form the sympathetic ganglionic anlage, that in it the 
indifferent cells (neurocytes of Kohn) undergo their differentiation into ganglion cells, 
nerve fibre cells, and chromotrope cells, and that only when the nerve fibres are 
formed does the connection take place with the ganglion cell. 
(b) In regeneration of nerves.—Gatzorti and Levi found in the new-formed tails 
of lizards that the first evidence of the new nerve fibres between the young muscle 
fibres was in the form of chains of fusiform cells linked end to end. Within the protoplasm 
of these cells a central granular filament—corresponding to the future axis-cylinder— 
