98 The Neurogha of the Spinal Cord of the Elephant 
pressing an individuality of the cell as is ordinarily implied. In the 
embryology of the spinal cord it is found that the spongioblasts are in- 
dividual cells only during the earliest stages of their development. 
Shortly after the cells of the neural tube are differentiated into those 
which will develop into neuroblasts and those which will produce the 
neuroglia (spongioblasts), there occurs a fusion of the latter resulting 
in the formation of a somewhat reticulated protoplasmic continuum or 
syncytium. After this fusion, the cytoplasm (syncytium) grows more 
rapidly than the nuclei divide and this results in the appearance of a 
marginal veil (Randschleier) about the inner, nucleated portion of the 
tube. The marginal veil at first contains no nuclei and appears as but 
an excrescence of the syncytium. Nuclei pass into it later. 
If attention be now confined to the marginal veil, which occupies the 
position of the future white substance of the spinal cord, it will be seen 
that it thickens, the reticulated syncytium continuing to grow, and 
later appears as larger bands of protoplasm in which are dispersed fre- 
quent nuclei. Though the nuclei have increased rapidly, their increase 
is not in proportion to that of their common cytoplasm. 
Soon the nerve axones begin to grow in and occupy the meshes of 
the syncytium and perhaps perforate it to a more reticulated condition. 
As the presence of the axones increases and as they grow in size, the 
bands of the syncytium necessarily become more and more attenuated. 
Finally when the axones acquire their medullary sheaths, the syncytium 
is sumply moulded in the inter-axone spaces, the larger of which usually 
contain its nuclei. The nuclei are so distributed that, in transverse 
sections of the spinal cord, usually but one nucleus will appear in a 
given inter-axone space, but two or even more may be so caught. In 
sections passing in the direction of the nerve fibers, there will of course 
be found many nuclei scattered along the third dimension of the space, 
appearing as a column of nucleated protoplasm. 
The syncytium may now be considered in two portions; that which 
more intimately surrounds the nuclei (endoplasm) and that which con- 
stitutes the attenuated bands or “ processes” between the more closely 
arranged nerve fibers (exoplasm). If two of the inter-axone spaces 
containing nuclei are near together, the endoplasm may be continuous, 
and the two areas of nucleated syncytium thus seen in transverse sec- 
tion may be considered as two neuroglia “cells” with anastomosing, 
processes. ‘Two such cells are shown in Figure 2. 
2. The exoplasmic portion of the syncytium becomes more homoge- 
neous while the endoplasm remains granular. In the more attenuated 
portions of the exoplasm (processes of neuroglia cells), neuroglia fibers 
