126 BYRNES. [VoL. XIV: 
greatly reduced, not only in thickness, but also in length. On 
the left side of the body the abdominal muscle has reached a 
very conspicuous development. Although the right limb is 
apparently free from contact with any of the myotome-deriva- 
tives, it has reached a development equal to that of the limb on 
‘the normal (left) side of the embryo. The two limbs are in 
every way comparable, not only in size, but also as regards 
their regions of differentiation within the limb-bud, as shown 
im Pleura) a5. 
One of the embryos shows the myotomes in the posterior 
limb-region reduced to one-half their normal length, even after 
six weeks have elapsed since the operation. A few scattered 
muscle-cells lie between the lower edge of the injured myotome 
and the limb-region. Whether some of the original myotome 
cells have escaped injury or whether those now present have 
regenerated is not clear from the sections. The injury was 
an extensive one, however, and must have affected the growth 
of the limb-rudiment had the limb been dependent on the myo- 
tomes either directly or indirectly for its development. The 
abdominal muscle is present, though somewhat reduced. 
Directly in front of the limb-region the abdominal muscle is 
well developed. Both the limbs are normal. 
The results of these experiments both on Amblystoma and 
Rana confirm the conclusions already reached from the study 
of normal embryos; z.e., that the muscles of the limbs are devel- 
oped wholly out of the mesoblastic cells of the somatopleure, 
the myotome-processes taking no part in the formation of the 
limb-muscles. First of all, the myotomes after injury remain 
permanently reduced in size. When the myotomes are greatly 
shortened there is often a corresponding shortening or con- 
traction of the entire injured side of the body. In the later 
stages of these embryos there is no evident attempt on the part 
of the myotomes to regain their normal proportions. Even 
when the myotomes have been but slightly injured, only the 
extreme ventral edges being destroyed, there is generally some 
permanent! indication of the injury in a reduction in the size 
of the muscle-plates. 
1 None of the embryos used in these experiments were kept longer than eight weeks. 
