268 



OR IGIN OF AMPHIBIAN PIGMENT 



derived cells will be merely the thickness of the coverslip away from microscopic examina- 

 tion. Such cultures should last for 8-10 days, or longer at lower temperatures. 



Recently (19^*^) Twltty cultured pigment cells from neural crests within capillary 

 tuhes measuring 0.25 to 0.14-5 in diameter. The neural crests were drawn into the tuhes by 

 oral suction, while submerged in sterile Standard ( Holtfreter's) Solution, and the tubes 

 were tilted slightly (within the Standard Solution) and the end of each tube farthest away 

 from the end containing the explant was embedded in non-toxic vaseline. This vaseline 

 acted as a plug, and at the same time held the tube in place. The tilting was achieved by 

 a mid-way ridge of vaseline, but this could be accomplished equally well with a knotched 

 paraffin ridge. The free end, i.e., where the explant Is located, was open to the culture 

 medium. During examination, the curved sides of the capillary tube acts somewhat as a 

 lens, magnifying the contained neural crest and pigment cells. Twltty found that pigment 

 formation in the capillary tubes was dependent upon substances diffusing from the nervous 

 tissue of the explant, and that the first cells to become pigmented were those found 

 deepest within the tube. He attributed this to regional differences in the concentration 

 of oxygen and pigment precursors or oxidases essential to melanin formation. 



Place in Petri dishes filled with Holtfreter's 

 solution, the tubes containing the explants 

 are held In position by partly imbedding 

 them in a row ridge of vaseline. The end 

 near which the explant lies is left open; the 

 opposite end is plugged with vaseline to pre- 

 vent any flow of fluid through tlie tube which 

 might De created by tipping or disturbance of 

 the dish. Semi-diagramraatlc drawing. 



A semi-diagrammatic drawing to repre- 

 sent the differential onset of melati- 

 Izatlon within cultures of embryonic 

 pigment cells developing in capillary 

 tubes . 



From Twltty, l^kk: Jour. Exp. Zool. 95=259. 



The record for this experiment will consist of a series of daily drawings of the 

 explants and the cells (pigmented and otherwise) which are derived therefrom. 



