MULTIPLE NEUROMATA OF THE CENTRAL NERVOUS SYSTEM. 705 
and an intercellular differentiation of the cell protoplasm—the transmitting substance 
—fine fibrils. 
SEDGWICK (1895) has strenuously upheld the view that the mesenchyme is not a 
tissue of branched cells but a reticulum with nuclei at the nodes. He believes that 
the neural crest gives rise to nuclei, which spread out in the mesoblast reticulum, 
and that the nerves are developments of the reticulum, 7.e. that the nerves are, as it 
were, a gathering up into bundles of the reticular strands. The development of a 
nerve, therefore, arises from the differentiation of a substance which was already in 
position, and this differentiation takes place from centre to periphery. The nerve 
roots are simply special enlargements of the connecting strands of the original reticulum 
joining the embryonic medullary wall to the general mesoblast reticulum. SEDGWICK’S 
position approaches, therefore, very near to that of HENsEN. 
ScHAPER (1897), together with K6iLiKzr, was one of the first to prove the precise 
origin of the Kezmzellen from the original epithelial layer of the primitive medullary 
tube. He further showed that these Kezmzellen, by mitosis, give rise to nerve cells 
(neuroblasts) and indifferent cells, and that the latter may differentiate in very various 
directions, e.g. into the cells of the granular layer of the cerebellum. Glia cells and 
peripheral neuroblasts may also arise from a further differentiation of the indifferent 
daughter cells of the primary cell groups. Scuaper thought that in certain primitive 
conditions, e.g. in amphioxus, the indifferent cells might possibly differentiate into 
nerve cells. Such indifferent cells may remain in an undifferentiated condition and 
later on might possibly play a réle in regenerative processes in the central nervous 
system. This term “indifferent cells” has been largely used by later writers on the 
embryogenesis of nerves. 
Kotsrer (1899), GurwirscH (1900), BaRDEEN (1902) all agree that the first stage 
of the nerve bundle is an entirely non-nucleated one. Koster chose as objects of 
study the embryos of Salmo, because here the first phases of development pass slowly. 
In Salmo the first anlage of the peripheral nerves is a narrow bundle of very fine 
fibrils proceeding from the spinal cord: the bundle shows no nucleus but pushes before 
it the layers of connective tissue, so that a single sheath covers the bundle. Later, the 
connective-tissue cells proliferate and penetrate the bundle. Koztster stated that the 
first traces of myelin appear before any nuclei are present in the bundle, and that the 
myelin development progresses peripheralwards. The first myelin appearance within 
the central nervous system is likewise before the differentiation of the glia cells, when 
there is present only a framework of ependymal cells and processes. 
SCHULTZE (1904-1906) takes up a quite independent position. A pronounced 
Supporter of the cell-chain constitution of the peripheral nerves, he holds also a 
modification of the protoplasmic bridge theory, for he denies the migration from the 
medullary tube. ScHuLTzk’s very extensive studies have covered the development of 
peripheral nerves in Amphibia, fowl, and mammal. His observations in a sheep 
embryo of 8 mm. show that the early motor roots consist of bundles of primitive fibrils 
TRANS. ROY. SOC. EDIN., VOL. XLVIII. PART III. (NO. 27). 102 
