TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 159 



attributed to increased defective connections with the central 

 reflex pathways involved in normal Umb locomotion, rather than 

 to a corresponding decrease in effective peripheral innervation 

 and structural deficiencies of the shoulder and limb. 



7. The high percentage of abnormalities in limbs transplanted 

 from two to three segments anterior to the normal position 

 (table 1 and figs. 2 and 3) is due to the fact that they are placed 

 in the environment of active gill-forming tissue. In these cases 

 the gill-producing properties of the tissue surrounding the trans- 

 plant markedly disturb the normal posture and differentiation of 

 the appendage. 



8. When the ectoderm and mesoderm are removed from the 

 entire external gill swelling (fig. 3) and a limb is transplanted 

 into the denuded area, abortive gills may develop from the 

 surrounding tissue (table 1). The results of the experiments 

 indicate that the tissue lying ventral to the typical gill region 

 possesses a relatively higher gill-forming capacity than does that 

 lying anterior or dorsal. 



9. That the outgrowth factors for the external gills reside not 

 only in the ectoderm of the immediate gill region, but extend with 

 diminishing degree of intensity into the surrounding ectoderm, 

 is evident. These observations, in so far as they could be made 

 in the present work, support the results obtained by Ekman 

 ('13 a, '13 b, '14) in his experiments on anuran forms. 



10. The hypoglossal nerve in Amblystoma is formed by the 

 union of the ventral rami of the first and second spinal nerves and 

 corresponds with the arrangement characteristic for urodeles. 



11. The entire ventral ramus of the second spinal nerve may 

 contribute nerves to the transplanted limb. In such cases the 

 hypobranchial musculature is supplied by the first spinal nerve. 



12. When the ventral portion of the first myotome is excised 

 with the gill mass, the anterior segment of the m. sternohyoideus, 

 the m. geniohyoideus, and the m. hyoglossus are absent on the 

 operated side. The hypoglossal trunk in such cases does not 

 assume its normal anterior pathway, but terminates in the 

 posterior segments of the m. sternohyoideus. 



