Although in genetic experiments on skin transplantation guinea pigs have been most widely used, mice and rats have been used in the present experiment because they have advantages as material for transplantation of embryonic skin. Fortunately the close analogy between the hair colors of all the groups of laboratory rodents suggests that results found in one group apply to the others.
This paper is a report of experiments on skin transplantation with mice and rats. The grafts have been of two types ; autotransplants, the transfer of the skin of an individual from one region of its body to another position, and syngenesiotransplants, the transfer of skin among close relatives (cousin to cousin, etc.). The syngenesiotransplants were nearly as sucessful as the autotransplants because of considerable previous inbreeding of the strain to which the related individuals belonged.
Five of the forty grafts of table were autogenous, the rest were syngenesiotransplants. All mere made according to the technique described in the first paper of this series (Reed and Sander, '37).
I t is important to note that all grafts were made with skin from newly born young or embryos. There is practically no pigmentation except in the retina of the eye, at any of these stages. I n the youngest embryos used as donors the recognized layers of the skin are just starting the processes of histological differentiation.
The grafts were placed on a newly born animal in some position other than that from which they had been taken. Grafts