132 BYRNES. [VoL. XIV. 
of normal embryos were afterward confirmed by experiments 
on Amblystoma and Rana. The myotome-processes were ex- 
cluded from the posterior limb-region on one side of the body 
by destroying the lower halves of the myotomes. Even 
under these conditions the posterior limbs were found to 
develop normally, although the myotomes and the myotome- 
derivatives were permanently reduced in size. After injury 
to the myotomes, the abdominal muscle regenerates, but the 
injury serves to delay its development and to keep it tempo- 
rarily away from the limb. 
The conclusions reached from the study of the limbs in the 
normal amphibia, and particularly from the experimental evi- 
dence, is that the limbs are of somatopleuric origin; z.¢., that the 
muscles as well as the cartilage and connective tissue of the 
limbs are formed from the somatopleure, and that the myotome- 
derivatives are not essential to the formation of muscles in the 
limbs. This conclusion brings into question the distinction 
that has been established between muscles derived from the 
mesothelium and those derived from the mesenchyme. I 
believe the results of the experiments on Amblystoma, and 
more especially those on the frog, must be interpreted as show- 
ing that in these forms, at least, the power to develop striated 
muscle has not been restricted to the myotomes; 2z.e., to meso- 
thelium, but that the mesenchyme-like cells of the somatopleure 
can and do give rise to voluntary muscles in the limbs. The 
experiments on the myotomes, therefore, furnish additional 
evidence to that already urged against the conception of a 
fundamental distinction between mesothelium and mesenchyme. 
