No. 2.] LIMB-MUSCLES IN AMPHIBIA. Lat 
days and were then killed and sectioned. They show that the 
trunk-segments have entirely escaped injury, although the myo- 
tomes in the proximal part of the tail have often been reduced 
to one-half their original length and the whole right side of the 
tail has become greatly contracted. This apparent migration 
of the injury seems to be due to the gradual growth of the tail. 
As the tail lengthens, myotomes that in younger embryos seemed 
to belong to the trunk appear later as anterior tail-segments. 
Only those cases have been considered and figured in the 
present paper which show marked traces of the early injury to 
the myotomes and in which only a very slight injury, if any, 
has been sustained by the somatopleure of the limb-region. 
Normal frog embryos killed on the 1oth and 11th of April and 
used as a check to injured embryos show that at the time of 
the operation neither the primary abdominal muscle-rudiments 
nor the posterior limbs had begun to develop. Therefore, no 
myotome-derivatives could at this time have been given to the 
limbs. 
Pl. XI, Fig. 19, serves as a control for the injured embryos. 
On the right side of the section the myotome is reduced to 
almost one-third of its length, and the abdominal muscle-rudi- 
ment on the right side has been completely destroyed. The 
limb-rudiment is uninjured and is almost as well developed as 
the limb on the normal side of the embryo. 
Sections through the posterior limb-region of an embryo 
killed three days after injury show that the myotomes on the 
side of the injury have been greatly reduced throughout the 
limb-region. The abdominal muscle-rudiment is wanting in 
corresponding sections, and there is little evidence of any 
attempt at regeneration. The limb-rudiment, which consists 
of only a slight aggregation of mesenchyme-like cells, is present 
and normal. Another embryo killed three days after injury 
shows a double abdominal muscle-rudiment on the side of the 
injury. A small mass of cells constricted from the myotome 
lies a little below and to the inner side of the myotome. At 
the ventral, outer edge of the myotome there is a second mass 
of cells similar to the first and occupying the normal position 
of the primary abdominal muscle-rudiment. 
