LIMB FIELD OPERATIONS 



279 



□ORSAU VIEW 



VENTRAL VIEW 



HETEROPLASTIC TRANSPLANTATION OF LIMB FROM A. TIGRINUM 

 TO RIGHT SIDE OF A. PUNCTATUM 



PIGMENTARY DIFFERENCES: 



This experiment is best demonstrated with the white axolotl, A. mexicanum, in limb 

 transplantations with the highly pigmented A. tigrinum. There are three main types of 

 pigment cells; Melanophores, with darker granular pigment; Xanthophores, with yellow 

 pigment; and Guanophores, with the metallic, gold or silver, guanin. The pigmentation 

 of a transplanted liinb always resembles that of the host, except in transplants involving 

 the white axolotl (Harrison, 1933). There are microscopic differences not only in color 

 of pigment cells, as suggested above, but in their size and shape. Incidental to part "A" 

 of this experiment, the effect of the host on the pigment of the donor limb can be deter- 

 mined in the A. tigrinum and A. punctatum transplants. If the rare white axolotl embryos 

 are available, this experiment would be most graphic and significant. 



The pigment cells are derived from the ganglion crest cells which migrate toward the 

 limbs in the earliest motile stage of the embryos (DuShane, 1934). A few xanthophores 

 and melanophores are developed when ectoderm from a normally pigmented embryo is 

 grafted to the limb bud of a white form. This suggests that the white axolotl has the 

 melanophores but that the ectoderm of the white axolotl lacks some of the activating prin- 

 ciple which is found in the ectoderm of the pigmented species. DuShane suggests that 

 the ganglion crest gives rise to cells which normally develop pigment and that a second 

 factor (ecto- or mesodermal) is necessary to activate the process. Periclinal and sec- 

 torial chimeras often appear. (See section on "Neural Crest Origin of Pigment", page 265. ) 



