ORIGIN OF AMPHIBIAN PIGMENT 271 



RECOED OF IN VIVO STAINING EXPEBIMENTS 



DISCUSSION: 



The neural crest arises as a strip of cells lying between the neural plate and the 

 dorsal ectoderm, this plate being separated from both of these structures during the 

 closure of the neural folds. It is now established that the neural crest is the principal 

 and probably the sole source of all pigment cells (except the tapetum) in all of the 

 vertebrates that have been studied (DuShane, 19^3)' Melanophores are found in the epi- 

 dermis and dermis, meninges, visceral mesenteries, peritoneum, and in close association 

 with the blood vessels throughout the body. This means that from the original source of 

 such pigment cells there has been very extensive migration. The forces involved in this 

 migration are illustrated in the capillary- tube isolation experiments of Twitty {19^k). 

 But the pre-migratoiy neural crest cells cannot be distinguished from their neighbors 

 because they show no pigment differentiation until about the time they reach their normal 

 destination. Such pigment cell differentiation includes: 



Melanophores - wide distribution, cells with brown to black melanin. 



Lipophores - dermis and epidermis, having diffuse yellow pigment (lipochrome) in 



solution. 

 Guanophores - pericardium and most lateral line organs, highly refractive, granular, 



golden yellow guanin crystals with metallic lustre. 



The pigment pattern may be used to identify different species of Amblystoma or Tri- 

 turus and frequently in heteroplastic transplantations there is evidence that both gene- 

 tic and environmental factors (such as humoral or contiguous cell influences) may be 



