Ross Granville Harrison 125 
spinal nerves, and which no doubt serves as a hindrance to their develop- 
ment. Again it seems to be practically impossible to remove entirely the 
motor elements from all regions of the cord. After several days the 
larvee, although almost completely paralyzed, regain some power of move- 
ment, showing usually a slight tremor in some part of their axial mus- 
culature, when stimulated mechanically. Sections show that in some 
Sp. C---- , 
v1 
/ eo / | / 
Nols =a 
| without Sheath Cells 
Fic. 4. Semidiagrammatic view of the nerves of the abdominal walls of a 
frog larva from which the ganglion crest had been removed as shown in Fig. 1. 
Only motor nerves are present and these consist of axis cylinders without 
sheath cells. 
segments very fine motor roots are present, and the ventral part of the 
remaining medullary cord contains in these regions a few large motor 
cells. These motor fibers supply, as the movements indicate, merely 
that part of the musculature lying close to the spinal cord. With the 
two exceptions below noted, no motor fibers whatever were found in the 
