SKIN TRANSPLANTATION IN FROG TADPOLES 401 



epidermis, which showed signs of having overgrown the graft. 

 In other words, the homoiotransplant acted as a foreign substance 

 placed in a wound, over which the epidermis migrated, as it 

 would over any wound. The melanophores were carried along 

 by the migration. 



The facts that pigment is constantly being formed in normal 

 epidermis and that epidermal cells migrate rapidly over a wound 

 are well known. Evidence of the specificity of protoplasm in 

 different individuals and the reactions set up between them has 

 been demonstrated by Loeb. Such reactions tend to delay heal- 

 ing, and in proportion to their violence. Because of this delay, 

 the epidermal cells surrounding a homoiotransplant will migrate 

 over it, thereby closing the wound in the shortest possible time. 

 Melanophores are carried along and the graft is pigmented. 

 When the graft animal is closely related to the host, almost 

 immediate healing takes place, the graft being accepted by the 

 host, so that migration of epidermis is not necessary. Melano- 

 phores are then formed in situ as the result of the normal growth 

 activity of the integument. In brief, both methods of pigmenta- 

 tion probably exist. Which one predominates, depends on the 

 kind of transplant made. In autotransplants formation in situ 

 is chiefly responsible for pigmentation, but in homoiotransplants 

 and heterotransplants epidermal migration is the primary cause. 

 Both methods concern epidermal melanophores, but onl}^ the 

 former method can give rise to dermal pigment cells. When 

 applied to the observations of Loeb, Winkler, Sale, Seelig, and 

 Dawson, this hypothesis seems to hold. It also explains the 

 behavior of the grafts on frog tadpoles. Further experiments 

 will determine its validity. 



PIGMENTATION OF THE CONJUNCTIVA CAUSED BY INJURY 



In examining a group of tadpoles obtained from a dealer, one 

 animal was found with several scars on its head. The left eye 

 was gone, the wound having been covered by a thin regenerated 

 layer, and the right eye was partly concealed "by pigmentation 

 of the conjunctiva. Attention is called to the fact that in frog 

 larvae the external structure of the eye is very different from that 



