ORIGIN OF AMPHIBIAN PIGMENT 



267 



Recently (1945) Twitty rotated the neural crest and adjacent somite material with inter- 

 esting results {see accompanying figures). This operation should be attempted but might 

 be varied in respect to position on the host. If the somites and crest are reversed, it 

 would be significant to make the 180° rotation at the level of the hind- or forelimb to de- 

 termine not only the lateration in pigment pattern but also in the muscular control of the 

 adjacent appendage. 



Fig. 2. Dorsal view of Triturus torosus larva showing the transverse strands which connect the paired 

 bands of melanophores located on the spinal cord. 



Fig. 3. (a) Extirpation of neural (trunk) folds. 



(b) Closure of "crestless" neural tube. 



(c) Block of tissue excised and grafted upside down in substitution of the somites of another 

 embryo (d G e). 



(d) Diagram of transplant in host (d.m. s. - dorsal margin of myotome). 



(e) Inverted somites and neural crest in host. 



(f) Modified distribution of melanophores in host. 



V. C. Twitty, 1945: Jour. Exp. Zool. 100:141. 



HETEROPLASTIC NEURAL CREST TRANSPLANTATIONS 



If Amblystoma punctatum and A. tigrinum larvae of stages #23 to #28 are available, 

 heteroplastic transplantations resulting in varied pigment patterns should be attempted. 

 If the white axolotl is available, the results are even more graphic. (See section on 

 "Transplantations" to determine the viable combinations. ) When Urodeles of different 

 developmental rates are used, this factor must be considered. In general, the graft tis- 

 sue should be from a donor slightly older than the host. Heteroplastic transplantations 

 are best made to the normal site, transferring dorsal ectoderm and ganglion crest, along 

 with some of the nerve cord, to insure presence of crest. 



Some suggested combinations : 



Amblystoma tigrinum crest stage #24 to A. punctatum stage #23. 

 Amblystoma punctatum crest stage #28 to A. tigrinum stage #23. 



