Our knowledge of iiiamnialian genetics is concerned with color genes to a large extent. Yet relatively little information may be found concerning the origin of the pigment producing cells in mammals. Satisfactory evidence has been offered as to the origin of the pigment cells in amphibia and birds and this provides a working hypothesis f o r our studies with mice.
Du Shane ('35) proved that tbe dermal melanophores of aniphibia originate in the neural crest. Dorris ('36) showed that neural crest cells from 6-10 somite chick embryos produce pigment in vitro while other parts of the same embryos fail to do so. She suggested, therefore, that the dermal melanophores of birds originate in the neural crest. The suggestion was shown to be correct by Dorris ('39) who grafted neural crest cells from colored donors to white hosts whereupon large patches of colored down developed. Eastlick ('39) used grafts of limb buds to host mesenteries to demonstrate the migration of melanophores. It was possible to regulate the amount of melanophore migration by the position of the limb bud upon the mesentery which acted as a barrier to the spread of the melanophores. Reed ('38) demonstrated that grafts of albino tissue upon colored hosts were invaded by host cells which were responsible f o r the development of colored hairs in the albino tissue. This experiment was upon mice and made use of a gene known as "black-and-tan" to prove that the observations resulted from cell migration and not from chemical diffusion of some Reacarch supportcd by a grant for genetics and cytology t o hfeGill TJniversitp from the Rockefeller Foundation.