No. 2.] LIMB-MUSCLES IN AMPHIBIA. I19 
six weeks after injury. Fig. 39 represents the posterior limb- 
region on the uninjured (left) side of the body. The myotome 
on the right side of the section has been almost wholly 
destroyed; the right side of the body has so contracted as to 
rotate the dorsal fin through an angle of nearly ninety degrees. 
Fig. 38 represents the posterior limb-region on the injured 
(right) side of the same embryo. The myotome, though not 
wholly destroyed, is greatly reduced in size, only a few muscle- 
cells remaining. The limb-rudiment has reached a conspicuous 
development, and is but little inferior to the one on the normal 
side. The slight reduction in size of the right limb is evidently 
due to some injury that resulted to the somatopleure of the 
limb-region when the myotomes were destroyed. Evidence of 
this is seen in the very general distortion of the whole right 
side of the section. 
Fig. 40 shows the right limb of an Amblystoma embryo 
killed forty-four days (six weeks and two days) after injury. In 
the limb on the normal (left) side of the body cartilage and 
muscle-fibrils are already present. In the limb on the injured 
(right) side the cartilaginous areas are distinctly marked out, 
although the cartilage is not so well developed as in the limb 
on the uninjured side. Differential stains fail to show the 
presence of muscle-fibrils in the right limb, although the muscle 
areas are distinctly marked out around the central core of carti- 
lage. Moreover, they correspond in every respect to the muscle- 
areas in the limb on the normal (left) side of the body. The 
entire mass of the right limb is less than that of the left limb, 
but the reduction in size, as well as the lesser degree of differ- 
entiation, in the right limb is evidently due to a general 
retardation of growth resulting from the injury to the right 
side of the body, and not to any difference in the zxds of 
tissue present. The permanently reduced size of the myotome 
bears witness to the extent of the original injury, and leaves 
little doubt that the region of growth of the myotome was 
completely destroyed. Even if the limbs were dependent on the 
myotomes for their muscle-tissue, it seems scarcely conceivable 
that the myotomes could, in the mutilated condition shown in 
the figures, contribute cells in sufficient numbers to enable the 
