Proceedings of the Association of American Anatomists V 
taken place. The greater part of the mesoderm of the trunk was left 
intact, although a small portion of the myotomes was necessarily removed 
with the cord. The embryos were kept alive until the yolk was absorbed. 
Aside from the defect caused directly by the operation, i. e. the absence 
of the dorsal fin, the dorsal part of the musculature and the total ab- 
sence of the spinal cord and ganglia, the development was normal. No 
voluntary movements in the trunk or tail of the embryos were observed 
nor was there any response to mechanical stimuli applied to these re- 
gions. Sections show that the differentiation of the trunk and _ tail 
musculature, which has no connection whatever with the nervous system, 
is normal. Muscle fibrille with cross striations and the sarcolemma are 
normally developed. Moreover the grouping of the fibres into muscles, 
as shown by the shape and size of the myotomes and the existence of the 
primary abdominal muscle, is also normal. |The only pathological feature 
observed was the somewhat excessive vacuolization of the muscle fibres, 
due no doubt to the suspension of function. 
A second series of experiments was made, in which embryos of the 
same stage as used above were allowed to develop in solutions of acetone- 
chloroform, 0.02-0.03 per cent in strength. Embryos reared in these 
solutions develop almost normally though more slowly than those kept in 
water. ‘They were never observed to make any voluntary movements, nor 
did they respond reflexly to mechanical stimuli, owing to the action of 
the drug upon the nerve centres... At the close of the embryonic period, 
when the yolk had been absorbed, the larvae were put into fresh water. 
After the expiration of ten minutes larvae of R. virescens had recovered 
sufficiently to react to stimuli and in a quarter of an hour were able to 
swim and to carry on respiratory movements. Larvae of R. palustris 
require a considerably longer time for their recovery. Sections of larvae, 
killed without being allowed to recover, show normal morphological differ- 
entiation of musculature and nervous system. 
The first series of experiments, in which the influence of the nervous 
system was removed by operation, shows conclusively that the normal 
differentiation of muscular tissue is absolutely independent of stimuli 
from the nervous system. The second series, where the nerve influence 
was suspended through the action of a drug, while not conclusive in itself, 
corroborates this result. It shows, moreover, that complex nervous and 
muscular mechanisms may develop without a functional stimulus and that 
they may be ready to perform their function as soon as the inhibition is 
removed, although in the frog normally the development of these func- 
tions is a gradual one. 
1Known commercially in the United States as chloretone. 
