118 BYRNES. [Vou. XIV. 
twentieth, inclusive. The posterior limbs in the frog tadpoles 
develop in the eleventh segments. Here the injury extended 
from about the sixth trunk-segment to the tail. After the 
operation the embryos were transferred to large shallow dishes 
of water. Care was taken to change the water frequently 
within the first few hours after the operation, until the wounds 
had entirely healed over. After that no further precautions 
were taken. Most of the embryos survived the injury and were 
kept in the laboratory in an apparently healthy condition for 
periods varying from one to eight weeks. 
An effort was made to restrict the injury as far as possible 
to the myotomes, leaving the somatopleure of the limb-region 
uninjured. I hoped, by completely separating the limbs from 
the myotomes, to be able to test the power of independent 
growth of the limbs when all connections with myotome- 
derivatives had been destroyed. In Amblystoma the posterior 
limb-rudiments arise so close to the ventral edges of the 
myotomes that it is extremely difficult to destroy the ventral 
portion of the myotomes without involving the somatopleure of 
the limb-region more or less in the injury. On this account 
Amblystoma is not a very favorable object on which to study 
the origin of limb-muscles by the experimental method. 
Notwithstanding the distortion that the right side of the 
body of Amblystoma usually undergoes in consequence of the 
incidental injury to the somatopleure, the right limb often 
reaches a surprising development, very little, if at all, inferior 
to the limb on the normal (left) side of the body. Pl. XII, 
Fig. 37, represents a section through the anterior part of the 
posterior limb of an Amblystoma embryo killed four weeks 
after injury. The right myotomes have not regenerated their 
own tissue perceptibly, nor have they given rise to the abdomi- 
nal muscle-rudiment. In spite of the injury to the myotomes, 
the limb has reached a surprising development. The limb on 
the injured (right) side of the body is in every way similar 
to the one on the normal (left) side, not only in general size, 
but also in the appearance of its component cells. 
Pl. XII, Figs. 38 and 39, show the injured and uninjured 
sides, respectively, of an embryo, in the posterior limb-region, 
