250 Growth and Tlistogenesis of Nerves 
secondary funiculi, seems to accompany the blood vessels which penetrate 
the nerve at various places along its course. In consequence of the 
irregular manner in which the septa arise, the fumieuli of the embryo, 
like those of the adult, branch and anastomose freely along the course 
of the nerve. New funieuli may also be added to the nerves during the 
process of plexus formation. 
In the further development of the nerve-trunks the most interesting 
questions are those concerned with the development of the myelin sheath 
and the sheath of Sehwann. The work of Vignal is of most funda- 
mental importance in’ this connection. In general the observations 
which I have made correspond with Vignal’s. Certain details in the 
development of the sheath of Schwann ean, however, be better studied in 
sections than by the teasing method employed by Vignal. Gurwitseh in 
studying this question made use of the Apathy gold-chloride method, 
which he found a speeifie stain for the membranous sheaths of the de- 
veloping nerve-fibrils. By the use of the Van Gieson stain T have been 
able completely to confirm the valuable work of Gurwitseh. 
In Fig. 13, b, at the left, two projecting masses of cells seem to be on 
the point of contributing new cells to the interior of the nerve bundle. 
sy the anastomosis of the flattened lateral processes of these intra-funt- 
cular cells, a membranous framework is formed which serves to divide 
the nerve-fibrils into groups. The membranes run parallel with the 
nerve-fibrils and thus appear as fine lines in cross-section (Tig. 13, 6) 
and usually so in longitudinal sections (Fig. 13, d¢). They may be 
stained in seetions, when Zenker’s fluid has been used, by the Van Gie- 
son or by the Mallory connective-tissue stain. ‘The processes extending 
from the intra-funieular cells have been taken by some investigators to 
be nerve-fibres. ‘Che longitudinal section shown in Fig. 13, d, might 
suggest a bipolar nerve cell. But the processes take a purple stain in 
the Van Gieson mixture and a blue stain by the Mallory method, while 
the nerve-fibrils take on quite a different color in each ease. Owing to 
the great delicacy of the membranous process of the cell, one is apt to 
obtain in teased preparations only the nucleus and a bit of the more 
granular entoplasm immediately about it. With eare, however, speei- 
mens may be obtained like that shown in Fig. 13, ¢, in whieh a consid- 
erable portion of the membranous exoplasm is retained intaet. ‘The 
membranous processes appear to have a slight fibrillation. Before the 
intrinsie cells of the developing nerve have become differentiated into 
sheath-eells they multiply by indirect division (Migs. 38, b, and 4). After 
they beeome thus differentiated, direct cell division takes place. The 
line of division may be in the long or in the transverse axis of the nucleus 
