MULTIPLE NEUROMATA OF THE CENTRAL NERVOUS SYSTEM. 703 
Hensew (1864) thought that it was almost impossible to believe that the nerve 
filament found the muscle fibre without a guide. He supposed that the junction 
is effected early, whilst the two are in contiguity, and that the subsequent elongation 
of the nerve fibres is due to the change in the situation of the muscle. Primary tracts 
were thus laid down in the embryo which, later on, by some unknown process trans- 
formed themselves into nerve paths. Ranvier held that the axis-cylinder is unin- 
terrupted from ganglion cell to periphery but that it passes through a series of cells. 
His position, therefore, approaches Hensen’s, and GEDoELST agrees with RaNvIER’s 
point of view. 
_ His (1879-1886) describes the first rudiments of the nerve under the form of 
chromogen material, without nuclei, passing out from the spinal cord. He showed 
that special differentiated cells in the medullary tube—primitive neuroblasts derived 
from the Keimzellen —send out processes which form the anterior root-bundles, which, 
when they reach the limit of the medullary tube, are surrounded by mesenchyme 
elements that later penetrate the bundles. According to His, the spinal ganglia are 
not outgrowths from the medullary tube, but have at first no attachment to it. 
‘His and KOLLIKER state that the connection is established by the ganglion cells 
sending out processes which reach the cord. Before the attachment takes place 
the ganglionic anlage of each side divides into two portions, the spinal ganglion 
and the sympathetic ganglion. His did not definitely establish the precise origin of 
the Keimzellen. 
_ KOLLIKER (1884) showed that the Kevmzellen of His are derived from the original 
epithelial layer of the primitive tube, that these Kezmzellen, through mitotic division, 
give rise to ganglion cells and glia cells, and that the fibres arise as non-nucleated 
processes of the ganglion cells and are continued as nerve fibres without any participa- 
‘tion of cells in their course. By means of frontal longitudinal sections of the cord 
with developing nerves KéiutKer has shown the naked compact bundles of nerve 
fibres. He states that the capsule cells of the spinal ganglia are mesodermic elements, 
and that these grow into the ganclion and gradually surround each individual cell. 
It is to be noted that Koriixer in his last paper has admitted that the Schwann cells 
are ectodermic elements and also that the growing nerve fibre at its tip is surrounded 
by a capsule of Schwann cells. 
Batrour (1888), in Hlasmobranchs, has shown that cells, migrating from the spinal 
“cord, become arranged into string-like groups with a wide attachment to the spinal 
cord. In these cells the nerve fibres develop. He remarks: ‘The cell structure of 
the embryonal nerve is a point on which I should have thought that a difference of 
opinion was impossible.” Batrour was one of the first to note the structure which is 
generally called the neural crest. He also pointed out that the sympathetic ganglia 
arise as swellings on the posterior groups of the spinal nerves and soon become removed 
from the latter to form isolated masses. 
Donen (1888-1892) has investigated the development of the nerves in Selachians, 
