Differentiation of Neuroblasts 37 
It will be observed that, while the percentage of loss in the size 
of the ganglia is not increased, is in fact slightly less than in the 
previous experiment, the loss in the ventral horn is greater, and 
this is exactly what would be expected, for the destruction of the 
muscles is much more complete, despite the fact that a slight 
projection of the wing remains, while the loss of sensory areas is not 
correspondingly great. The loss in the posterior horn is of the 
same nature as in experiment 538, and no attempt was made to 
determine this quantitatively. Fig. 15 is a photograph of a cross- 
section of the spinal cord in the region of the operation. 
Experiment 225. This embryo was operated on after a period 
of incubation lasting 74 hours, and was returned to the incubator 
for 5 days 1 hour, making its age at the time of preservation 8 days 
3 hours. A small portion of the wing was left, but the ventral 
portion of the body wall from the wing to the leg was not developed, 
and sections showed some distortion of the pelvic region. Detailed 
observations were, however, confined to the part anterior to the 
leg. Figs. 7 and 8 are photographs of this embryo. 
The scapula was affected little if any, and a large part of the 
humerus was present; the muscles dorsal to these bones are 
normally developed. Only the most anterior portions of the cora- 
coid and sternum are present and the muscles are as follows :— 
the subscapularis, deltoides, latissimus dorsi, triceps and pectoralis 
secundus are all present, but more or less abnormal; only remnants 
of the biceps and pectoralis major are to be found, while the teres, 
subclavius, pectoralis secundus and tertius are entirely wanting. 
Fig. 5 shows the chief bones and muscles. 
The distribution of the peripheral nerves is shown in Fig. 34. 
Branches innervating the pectoralis and biceps are smaller on the 
operated side, and no trace of those normally reaching the missing 
muscles is found. Quantitative estimates of the loss throughout 
the injured region were not made for this specimen, but measure- 
ments were taken here and there and the results agreed with those 
obtained in the two previous cases studied. ‘The defects in the 
spinal cord were also of the same nature, and are shown in 
Fig. 16. 
The effect of the injury in the region between the wing and the 
