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S. R. DETWILER 



first myotome, the anterior portion of this muscle is entirely 

 lacking as is its derivative,, the m. geniohyoideus. No mention 

 was made of the genesis of the m. hyoglossus, but from the 

 present experiments, the evidence suggests that this muscle 

 also arises from the anterior segment of the m. sternohyoideus, 

 for when the anterior segments of this muscle are lacking, the 

 m. hyoglossus is also absent. 



The ventral portion of the first myotome in Amblystoma is 

 in intimate relation to the gill mass (fig. 1). The deficiencies 



Fig. 9 Left lateral aspect of case AA2S21 drawn seven days after the operation. 

 X 10. 



Fig. 10 Right lateral aspect of case AA2S21 drawn seven days after the opera- 

 tion. The limb bud occupies the region of the second and third external gills. 

 The first gill (EGl) is considerably smaller than the normal (fig. 9). X 10. 



in the hypobranchial musculature on the operated side indicate 

 that in preparing the wound for the limb rudiment, the ventral 

 portion of the first myotome, as well as a portion of the second, 

 was excised. 



Case AA2S21. In this experiment, the ectoderm and mesoderm 

 of the entire gill region were excised and the Hmb rudiment was 

 transplanted into the excavated area, as seen under conditions 

 indicated in figure 3. The denuded limb area was covered with 

 indifferent ectoderm. Seven days after the operation the ap- 

 pearance of an external gill was seen between the heterotopic 

 limb bud and the balancer (fig. 10, cf. fig. 9). At fourteen days 



