No. 2.] LIMB-MUSCLES [N AMPHIBIA. 129 
are more readily explained by the alternative hypothesis ; z.e., 
that the abdominal muscle has regenerated from its own tissue 
in an uninjured part of the body, rather than from the 
injured myotomes themselves. This suggestion is made prob- 
able by the fact that the connection between the regenerating 
abdominal muscle and the ovzgzzal abdominal muscle-rudiment 
is always unbroken, the regenerating muscle always passing 
gradually into the normal muscle, which lies ventrally in a 
more anterior part of the body. This could hardly be the case 
if the regenerating muscle were formed by a second series of 
ventral processes from the myotome. 
Although the rudiment of the abdominal muscle regenerates 
sooner or later, the new muscle is often smaller than the corre- 
sponding normal one on the uninjured side of the body. It is 
also often much nearer the ventral edge of the myotomes than 
the one on the normal side. These experiments, showing that 
the abdominal muscle always regenerates, make it extremely 
probable that in the original experiments the rudiment of the 
abdominal muscle was actually destroyed, but that it has regen- 
erated and in some cases has reached almost its original size. 
Although the rapid regeneration of the rudimentary abdominal 
muscle often brings about normal relations between the muscle 
and the limb-rudiment, the injury often suffices to check the 
development of the myotomes and to keep them, as well as the 
myotome-derivatives, temporarily from coming in contact with 
the limb-rudiments. 
The most striking fact in connection with the injured 
embryos is that, notwithstanding the permanent reduction in 
the size of the myotomes and the consequent diminution in the 
size of the myotome-derivatives, the lémbs are normal. This 
normal development of the limbs can only be explained on the 
ground of independence of the limbs and the myotomes. If 
the limbs are normally dependent on the myotomes for so large 
a proportion of their entire mass as is represented by the mus- 
cles, why, when the source of the muscles has been destroyed, 
is there no corresponding diminution in the size of the limbs ? 
There is no reduction in the limbs corresponding to the reduc- 
tion in the muscle-structures, except in those cases where the 
