140 BYRNES. 
EXPLANATION OF PLATE XII. 
(All drawings made with the camera.) 
Fic. 37. Cross-section through the posterior limb-region of an Amblystoma 
larva killed four weeks after injury. Myotome greatly reduced. Right limb 
present. 
Fics. 38 and 39. Sections through the right and left posterior limbs, respectively, 
of an Amblystoma larva killed six weeks after injury. 
Fic. 40. Cross-section through posterior limb-region of Amblystoma. Muscle- 
regions beginning to develop in the right limb. 
Fics. 41 a and 41 6. Two cross-sections through the posterior limb-region of a 
tadpole killed nine days after injury. Fig. 41 a@ more posterior than 414. Right 
myotome almost wholly destroyed. Medullary tube wanting. Limb-rudiments 
equal and normal. 
Fics. 42 and 43. Cross-sections through right and left limb-rudiments of an 
embryo whose myotome-derivatives were destroyed. Both limbs are beginning to 
show a condensation of nuclei around the periphery to form muscles. 
Fic. 44. Section of Fig. 41 a, enlarged, showing relative number of nuclei in 
right and left limbs. 
Fic. 45. Enlarged section of Fig. 33 in Pl. XI. Posterior abdominal muscle 
wanting on right side of embryo. Right limb normal. 
Fic. 46. Cross-section through middle region of right posterior limb of tadpole 
killed thirty-two days after injury. Posterior abdominal muscle-rudiment wanting. 
Limb normal. 
Fic. 47. Middle region of left posterior limb of same embryo. Comparison of 
Figs. 46 and 47 shows the two limbs equal, although in Fig. 46 the myotome- 
derivatives are wanting. 
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