58 I / Gee GP Shorey 
same scale as 4 gives the course of these nerves on the in- 
jured side. ‘The sciatic plexus itself, at the point marked (4), is 
about 75 per cent smaller on the operated side, and branches (1) 
and (2) are proportionately decreased. ‘The branch marked (3) 
goes to the bladder and is of normal size. Following backward to 
the individual nerve trunks which form the plexus, II is found to be 
40 per cent and III, 64 per cent smaller on the operated side. Of 
the two ganglia which correspond to these nerves, a rough but 
conservative estimate shows one to have lost at least 50 per cent 
in volume, while the other has lost about 334 per cent. Fig. 27 
was taken from a transverse section of the spinal cord in the region 
of the second nerve of the sciatic plexus. ‘This is fairly typical of 
the cord throughout the injured region, although occasionally a 
section 1s found in which there 1s little difference between the two 
sides. 
But while there is a decided defect in the nervous system at this 
period, 33 days after the first removal of the limb, from this speci- 
men alone it is impossible to determine whether it is dueto degener- 
ation or to failure to develop, although there is no evidence of 
degeneration. As will be seen from the figures the nerve trunks 
are, at this time, well established, and differentiation within the 
spinal cord, if not complete, is at least well advanced. It is there- 
fore necessary to examine younger specimens for signs of degener- 
ation, and to determine as nearly as possible the period at which 
differentiation of the motor neurones is complete. 
Younger Embryos. I found that the length of time which must 
elapse after the operation before a defect in the nervous system 
appears depends on the degree of differentiation attained, and 
neither age nor size is an exact criterion of this. Size is a much 
better measure, but my records were made with time as the 
standard, with some comparative data in regard to length and the 
rapidity of growth. In one specimen in which the limb was slightly 
larger than usual at the time of its removal, and in which the 
larva continued to growrapidly, a slight diminution in the size of 
the motor : orn can be demonstrated at the end of ten days. Fig. 
26 is typical of the spinal cord in the operated region of this 
embryo, but there are sections in which no difference in the two 
