MULTIPLE NEUROMATA OF THE CENTRAL NERVOUS SYSTEM. 713 
in the cord and spinal ganglion. The small groups of neuroblasts become approximated, 
their protoplasm fuses into a single mass, and certain of the nuclei undergo regressive 
changes and finally disappear. Not only the body of the nerve cell but also its pro- 
cesses are formed by this fusion of neuroblasts. 
La Prena (1904) has used chiefly Cajal’s and Donaggio’s staining methods for 
neuro-fibrils. He supports the view of the independent origin of nerve fibres and nerve 
cells. His conclusions are as follows :—The nerve cell does not take part in the forma- 
tion of the nerve fibre; the nerve fibre in the first stage of its development has no 
connection with the nerve cell ; the peripheral and central nerve fibres are developed 
from cell-chains; the protoplasmic processes, like the axis-cylinder processes, are 
also derived from cell-chains; and the neuro-fibrils of the nerve cell are a late 
product of differentiation—in the chick they do not develop before the tenth day of 
incubation. 
Fraeniro (1905), in the chick embryo, has given a description of the genesis of the 
central nerve fibre from chains of nucleated cells. By the use of Donaggio’s intracellular 
fibril method he was able to follow the disappearance of the nuclei and the formation 
of the neuro-fibrils. The fibre resembles a ribbon or thread with fusiform swellings at 
regular intervals. It is inferred that each swelling of the thread represents a cell, whose 
nucleus is quite evident and whose protoplasm is elongated into two filaments which 
unite with the filaments of two contiguous cells. The nucleus tends gradually to disap- 
pear, and probably its substance is diffused into the protoplasm and transformed into the 
axis-cylinder. In the cells of the same thread the nuclei are seen in various phases of 
transformation, and as they fade the fusiform swellings disappear and the margins of the 
thread tend to become parallel. Fracniro agrees with La Prena that the axis-cylinder 
is never seen in connection with the nerve cell before the tenth day. This differs from 
the observation of Casa, who states that by the fifth day all the axis-cylinders have 
reached their destination and can be traced emerging from the cord by the anterior roots 
as well-formed tubes of white matter. 
CaNTELLI (1907) has examined the structure of the neuro-fibroblasts in the central 
nervous system of the chick by means of Donaggio’s neuro-fibril method and subsequent 
staining with neutral red. There were found in the spinal cord long bands with uniform 
spindle-shaped swellings, in the middle point of which were dark granules: these gran- 
ules stained intensely with the nuclear stain and were thus taken to correspond to 
nuclear substance. 
Harpesty (1905), studying the developing spinal cord of the pig, noted the presence 
of half-moon or signet-ring-shaped cells encircling the nerve fibres. In early stages the 
axis-cylinders run as fine fibrils in a syncytium in which nuclei lie. During the period 
at which the process of myelination is at its height, these are distinct cells with con- 
siderable protoplasm lying in relation to the developing nerve fibre. The protoplasm 
of the cells at first often completely encircles the growing myelin sheath, but with its 
further growth the protoplasm of the cells is used up. It is suggested that the signet- 
TRANS, ROY. SOC. EDIN., VOL. XLVIII. PART III. (NO. 27). 103) 
