44 M. L. Shorey 
operations having been performed by him in the investigation of 
another problem. 
1. After Six Days of Incubation 
Experiment 10. This embryo was 6 days old when the wing 
bud was amputated, and when preserved 4 days later it was 
found that only the distal part of the limb had been removed, a 
stump extending nearly to the elbow being left. Although there 
were some abnormalities in position, shape and size of other parts, 
it will be seen by consulting Fig. 33,4, that the principal nerves 
involved would be the branches lettered fw and fw. As the loss 
would necessarily be small in amount this embryo was not studied 
with much detail, but there was a slight but evident defect in the 
ventral horn in the region of the 14th nerve. 
2. After Five Days of Incubation 
Experiment 5. The period of incubation before the operation 
in this case was 5 days, and when examined 2 days later it was 
found that a small stump was left in the region of the right wing. 
By referring to the figures for the normal side of Experiment 404, 
which was approximately in the same stage of development as this 
embryo at the time of the operation, it will be seen that the 
branches of the peripheral nerves must have been sectioned by the 
operation. ‘The chief point to be gained from this embryo is that 
there is evident degeneration of the fibers of the pectoralis, biceps, 
and triceps nerves. The degeneration extends for only a short 
distance toward the center and no abnormal cells are found in the 
motor nucleus. 
This is, however, smaller; sothat there was evidently a lack of 
development as well, and this would be expected, for the motor 
nucleus does not appear to become complete and separated as a 
distinct unit from the rest of the spinal cord before the 6th day. 
Cajal states that it is complete by the 5th day, but as the stage of 
development which he has figured for the 5th day differs but little 
from that which | have regarded as typical for the 6, the discrep- 
ancy probably arises from the difficulty in timing the actual 
period after fertilization. Moreover the defect in the motor nu- 
