SKIN TRANSPLANTATION IN FROG TADPOLES 403 



the dermal melanophores were present throughout the conjunc- 

 tiva, although by no means so numerous as epidermal melano- 

 phores. Subsequent changes were very slow and involved only 

 a gradual increase in the number of pigment cells. A count of 

 the pigment cells in the conjunctiva on the tenth week gave the 

 following totals : ninety-two epidermal melanophores, twenty-one 

 dermal melanophores, and sixteen xantholeucophores. The left 

 eyes of these animals remained normal. 



The experiments were repeated on five other animals with the 

 same results. It was found, further, that there was a minimum 

 degree of injury, following which pigmentation was produced, 

 and that pigmentation was probably restricted to that region 

 of the conjunctiva which had been injured. The latter observa- 

 tion was furnished by a single case, in which only the ventral 

 half became pigmented. It was assumed, therefore, that only 

 the ventral half had been sufficiently injured. The determina- 

 tion of relations between the stimuli and the reaction will be the 

 subject of further investigation. 



The experimental production of pigmentation in the conjunc- 

 tiva, such as has been here described, has an important bearing 

 on several subjects. In the first place, it furnishes further evi- 

 dence on the mechanism of epidermal wound healing. There is 

 no doubt that the epidermal melanophores which were present 

 in the conjunctiva twenty-four hours after the injury were car- 

 ried along by the migrating epidermal cells from the surrounding 

 skin. The centripetal movement of epidermis occurred in re- 

 sponse to the stimulus produced by the wound. This reaction 

 has been discussed elsewhere. The radial arrangement of the 

 cells and their sudden appearance can be explained in no other 

 way. The subsequent increase in the number of epidermal 

 melanophores, as well as the appearance of the dermal melano- 

 phores and xantholeucophores was probably the result of forma- 

 tion in situ. This secondary step, one of mitotic multiplication of 

 integumentary cells, is like that which takes place in normal re- 

 generation of skin. The writer believes that this is more prob- 

 able than that the increase of pigment cells is due to continued 

 migration. 



