SKIN TRANSPLANTATION IN FROG TADPOLES 397 



very weak, of short duration, about thirty-six hours. From the end of 

 that time to the fortieth day after the operation no changes were notice- 

 able. On the fortieth day, a concentration of melanophores along the 

 edges of both grafts was recorded. Following that appearance the 

 pigmented border gradually widened, spreading over the grafts, until, 

 on the eightieth day, the last clear areas were pigmented, and the whole 

 of each graft was dark gray. During this period, pigment granules were 

 abundant in the epidermis; many irregular masses of melanin could be 

 found, and parallel arrangement of the melanophores was not at all 

 prominent. Sections of LB 36 fixed on the ninetieth day showed that 

 the dermis was being replaced by the host; that a few dermal melano- 

 phores were present, and that the epidermal melanophores and melanin 

 granules were abundant. 



When contrasted with the first of the three cases described, 

 these latter two grafts show striking differences. In the first 

 place, there was a difference of seventy-nine days in the length 

 of the pigmentation process. At the end of the longer period, 

 the number of melanophores in the graft was very large, causing 

 a deep shade of gray, while after the shorter period, the melano- 

 phores were few, although evenly distributed. Secondly, mela- 

 nin granules and irregular masses of pigment in LB 35 and 36 

 were very abundant, while in the other case they were negligible. 

 Thirdly, the sizes and the ages of the animals were very different. 

 The first graft was taken from a tw^o-year-old-tadpole and placed 

 on an animal of half that age. Therefore, the animals were not 

 closely related. The other grafts were interchanged between 

 animals of the same age, size, and appearance, belonging to a 

 group of tadpoles which had been collected from the same source. 

 These are good reasons for believing that they were closely 

 related. 



The other homoiotransplants may be arranged between these 

 two extreme cases. The duration of the process was about six 

 weeks. The melanophores were often arranged parallel to each 

 other, and pigment masses and granules w^ere usually not present, 

 especially in the early history of the grafts. The concentration 

 of melanophores along diagonal lines w^as very frequent. Material 

 sectioned at different stages of pigmentation ahvays showed 

 the presence of epidermal melanophores. Only a few dermal 

 melanophores were found. In the older grafts the replacement 



