128 BYRNES. [Vou. XIV. 
abdominal muscle was wholly wanting. There is in nearly all 
of the injured embryos a dorso-ventral growth from the myo- 
tome in the posterior part of the body, where the rudiment of 
the abdominal muscle and the myotomes retain their connection 
with each other. This down-growth from the myotome, such 
as is shown in Pl. XI, Figs. 23, 24, and 27, occurs in connec- 
tion with the regeneration of the abdominal muscle, and not in 
connection with the regeneration of the myotome itself. 
Directly in front of this place of union of the abdominal 
muscle with the myotome (Figs. 23, 27), there is no cor- 
responding down-growth from any of the myotomes, but the 
rudimentary muscle is always present some distance below 
them (Figs. 25, 28). 
Since all the myotomes of the same embryo were injured at 
the same time, I expected to find them all simultaneously 
undergoing similar regenerative changes, but I have never 
found this to be true. Iam unable at present to satisfactorily 
explain the regeneration of the abdominal muscle, and can 
only suggest one of two hypotheses by way of explanation : 
either the abdominal muscle is formed anew (by the injured 
myotomes) from a second series of myotome-processes, or it is 
regenerated independently of the myotomes from an uninjured 
part of the muscle itself. 
On the hypothesis that the abdominal muscle regenerates 
from a series of down-growths from the injured myotomes, the 
anterior myotomes would have to regenerate their ventral 
myotome-processes before the posterior myotomes regenerated 
theirs, for the position of the regenerated muscle-rudiment in the 
body-wall is almost invariably od/zqgue ; the more anterior end 
being much further ventral to the myotomes than the posterior 
end of the muscle, which always remains in contact with the 
myotome from which it was originally derived. This hypothe- 
sis could account for the regeneration of the abdominal mus- 
cle in the posterior part of the body where the myotome and 
the muscle-rudiment are connected, but it cannot explain the 
regeneration of the abdominal muscle in front of this region. 
The oblique position of the regenerating muscle and the 
complete separation of the muscle from the anterior myotomes 
