REGENERATION IN VERTEBRATES 297 



of carbon to the surface and then its extrusion were most evident 

 among the larger concentrations but presumably occurred among the 

 scattered granules as well. When Nile-blue sulphate was infused from 

 below into the early regenerate, it was concentrated at first within 

 scattered mesenchymatous cells (Singer and Ray, 1957), but then, 

 after a few days, it appeared within the epithelium located in wander- 

 ing cells, in debris, and perhaps in epidermal cells. Our experiments 

 showed a movement of materials as in a stream from the blastema into 

 and through the epidermis to the outside. 



Ide-Rozas ( 1936; see also Roguski, 1953 ) remarked upon the 

 phagocytic activity of tadpole epidermis in the early days after tail 

 amputation. Epidermal cells of the wound contained debris which they 

 gathered as they moved over the wound coagulum. There were no 

 obvious pseudopodial moN'ements seeking out the debris but rather a 

 "passive" sweeping-up of particles encountered on the way. Ide-Rozas 

 injected carmine granules under the skin of young tadpoles and mature 

 animals. Within 24 hours the epidermal cells were charged with 

 granules. 



In the induction of supernumerary limb regenerates by deviated 

 nerves in the newt, Bodemer ( 1958 ) 'observed that debris was col- 

 lected within the intercellular spaces and the cells of the epithelium. 

 He dusted charcoal upon the open wound and found that it was culled 

 by the epidermis as it closed over the wound and then was expelled. 



Vilter (1933) described the transfer of melanin granules from 

 melanocytes to epidermal cells. He also showed that Axolotl epidermal 

 cells cultivated in a medium containing scattered melanin granules 

 harvest the granules in large number and concentrate them in a supra- 

 nuclear zone. There is still other evidence from tissue culture that 

 epithelial cells are phagocytic; for example, Matsumoto ( 1918 ) showed 

 that corneal epithelial cells of the frog will concentrate pigment gran- 

 ules, particles of carmine, Chinese ink, and other foreign substances 

 in a perinuclear position ( see also Ishikawa and Shimomura, 1927, for 

 epithelium of frog tongue, gall bladder, and urinary bladder ) . 



In our laboratory we and our associates have had occasion to in- 

 fuse solutions of many substances into the growth ( Singer, Weinberg, 

 and Sidman, 1955; Singer, Flinker, and Sidman, 1956; Singer, Davis, 

 and Scheuing, 1960). We have noticed regularly that the melanocytes 

 of the blastema are sensitive to cytolysis (see also Lorincz, 1954), are 

 destroyed, and their granules are scattered in the subepidermal region 

 ( Ide-Rozas, 1936 ) . The granules are swept into the epithelium, where 

 they are gathered by the epidermal cells. Perhaps not all of the gran- 

 ules in the epithelium arise from disrupted melanophores; it is possible 

 that the epidermal cells are induced by pathological processes to form 

 others ( Billingham and Medawar, 1950 ) . Fraisse ( 1885 ) observed the 



