128 Experiments on the Development of Peripheral Nerves 
its formation. In addition to these normal cases there are several 
experiments at hand, which show that even in the frog embryo the 
spinal ganglion cells are by themselves capable of forming long 
peripheral nerve fibers. The cases in question are those in which rela- 
tively small fragments of ganglia had been dislocated or transplanted. In 
one such case four ganglion cells, transplanted to the abdominal wall, were 
found giving rise to a long nerve, which ran free through the peritoneal 
cavity of the larva. This nerve consisted solely of bundles of fibrille 
without cells and could be traced for a distance of nearly two millimeters. 
These results differ from those recently reported by O. Schultze (Op. 
cit.) based also upon the study of the amphibian larva. It is not possible 
to discuss this work in detail here, but it may be pointed out that by 
confining his studies to relatively late stages, Schultze has missed the 
early and fundamental phases of development and thus is led to con- 
sider the purely secondary connections of the sheath cells with the nerve 
fibers as a primary genetic relation. 
We may now take up the second great question, viz., the origin of the 
connection between ganglion cell and end organ. According to the one 
view a protoplasmic process grows out from the ganglion cell, makes its 
way through tissues and ultimately reaches its end organ, gradually dif- 
ferentiating into a nerve fiber. According to the second view (Hensen’s 
hypothesis) protoplasmic connections remain between cells after division ; 
those that are used, i. e., that function as conducting paths, persist and 
differentiate into nerves, the remainder disappearing. 
According to Hensen’s hypothesis the nerve paths are thus developed 
much earlier than they seem to be, and they are present for some time 
before they become visible. If we consider the embryo-of a stage just 
before the nerves do become visible, then the two theories might be distin- 
guished as follows: according to the one, the center (ganglion cells) is 
the all important factor in forming the nerve; according to the other 
the nerve is formed in situ in the peripheral path. This difference affords 
the basis for experimentation, though unfortunately the distinction is not 
so clearly cut as could be desired, for the first view does not deny the 
importance of the periphery in forming paths along which the develop- 
ing nerve grows, nor does the second altogether disclaim the influence of 
the ganglion cell upon the differentiation of the primitive protoplasmic 
connections into nerve fibers. 
The first set of experiments consisted in the extirpation of the center. 
7 Virchow’s Archiv, Bd. XXXI, 1864. Die Entwickelungsmechanik der Ner- 
venbahnen im Embryo der Saugetiere. Kiel und Leipzig, 19038. 
