706 DR ALEXANDER BRUCE AND DR JAMES W. DAWSON ON 
converging towards the myotome and that these are traversed by innumerable elongated 
nuclei. In later embryos only the distal end of the nerve shows many nuclei, and this 
end may split up into a brush of fibrils amongst which lie typical elongated nuclei. 
The picture is that of a syncytium, for cell limits cannot be recognised. Regarding 
the sensory nerves, SCHULTZE states that below the corium in amphibian larvee he finds 
a network of very delicate bipolar and multipolar cells with long processes continuous 
with nuclear rich nerve fibres. Here there is no fusion of individual cells into chains 
but a continuous sensory syncytium spreading over the whole surface of the body by 
the continued preservation of intercellular connections, following mitotic division of 
the nucleus. ScHuLrze regards the nodal points as peripheral neuroblasts, and as he 
finds them beneath the skin in all mammals, he concludes that the whole nervous 
system in its specific elements is constructed out of millions of central and peripheral 
neuroblasts. This becomes clearer the further back we go in phylogeny, for the diffuse 
nervous system of the vertebrates and invertebrates, as far as it is known, consists of 
networks of cells and processes. This continuous integumental network of nerve- 
forming cells proves the analogy of the nervous system in all animals and gives the 
key to the understanding of the morphogeny of the nervous system from the Coelem- 
terates to man. SCHULTZE’S very careful and exhaustive studies have convinced him 
that the present-day neurone teaching rests on no indisputable observation; that a 
right understanding of the nervous system in its ontogenetic and phylogenetic relations 
can be gained only on the ground of its cellular or syncytial structure from elements, 
central and peripheral, which are termed neuroblasts; that these elements are originally 
of equal significance and become partly central and peripheral ganglia or nerve-cells, 
and partly elements which serve for the syncytial structure of the peripheral fibres, 2.e. 
peripheral nerve fibre cells. ‘The chief point is that neuro-protoplasm does not grow 
out, but represents ab ovo a “continuum” formed by a few cells and their intercellular 
bridges. Whether the neuro-fibrils or the interfibrillar substance is the conducting 
part ScHuLtzE does not decide. In his latest paper he states that the impetus to the 
formation of the neuro-fibrils may proceed from the central organs as from a dominating 
centre—proceeding peripheralwards into the preformed syncytial channel. 
Koun (1905).—Koun’s researches into the development of the dorsal nerve root 
in mammals and the development of the sympathetic nervous system mark a distinct 
advance in our knowledge of the structure of the peripheral nervous system. After 
his work appeared even KOLLIKER and LENHOossEK admitted the ectodermal origin of 
the sheath of Schwann cells. Koxun looks upon the problem of the origin of the 
sheath of Schwann cells as the crux of the question. If these were really acquired 
mesodermic elements, it would be impossible to defend the view that they have a 
share in the formation of the peripheral nerve fibre, but if they were of ectodermic 
origin the chief bulwark of the theory of the unicelluJar origin of the peripheral 
nerve fibre fell to the ground. It need hardly be said that the question is by no 
means settled, and distrust of the ectodermic origin, and specially of the nervous 
