No. 2.] LIMB-MUSCLES IN AMPHIBIA. 127 
Although the myotomes plainly show that they have been 
reduced by the operation, and the regions from which the myo- 
tome-processes develop have been destroyed, a rudiment of the 
primary abdominal muscle is always present, even though it is 
often greatly reduced in size. The presence of an abdominal 
muscle-rudiment, together with a greatly reduced myotome on 
the side of the injury, might seem to indicate that the primary 
abdominal muscle-rudiment had formed prior to the time of 
injury to the myotomes and had possibly escaped being de- 
stroyed when the myotomes were injured. Normal embryos 
killed on the same days that the others of the set were injured 
and used as a check to the injured series show that the ventral 
myotome-processes or primary abdominal muscle-rudiments are 
still in connection with the myotomes, even in the anterior 
part of the body, where the connection between the myotomes 
and their ventral processes is earliest lost. In the posterior 
limb-region of the “‘check’”’ embryos the abdominal muscle- 
rudiment is represented by only the extreme ventral edges of 
the myotomes, which had not begun to be constricted at the 
time of the operations. 
It is not probable that the abdominal muscle-rudiment in 
corresponding embryos always escaped being destroyed through- 
out the extent of the injury when the myotomes have been as 
greatly reduced as shown in Pl. XI, Figs. 24 and 25. I have 
made several sets of experiments on the tadpoles of Rana 
palustris to see if the primary abdominal muscle really does 
always regenerate after it has once been destroyed. These 
experiments consisted in destroying the ventral halves of the 
myotomes before the primary abdominal muscle had begun to 
develop. The injury was much more extensive in these experi- 
ments (made in the spring of 1896 and of 1897) than it was in 
the original ones (made in 1895), for it was not confined to the 
limb-region, although it often included the limb. 
The results of the experiments show that when the rudiment 
of the abdominal muscle is destroyed along with the ventral 
edges of the myotomes it always regenerates, the process of 
regeneration beginning within a few days after the injury. I 
have never found an embryo in which a rudiment of the 
