396 WILLIAM H. COLE 



of melanophores, although the graft never, even in the oldest 

 cases, became as dark as back skin. Hasty examination indicated 

 that nearly all of the melanophores were epidermal, and a study 

 of sections confirmed that observation. Only a few scattered 

 dermal melanophores were found in old grafts. But epidermal 

 pigment cells were abundant. Many of the epidermal cells con- 

 tained pigment granules in varying amounts. Some of them were 

 nearly filled by pigment, and could easily be interpreted as 'young' 

 melanophores. Another proof that the pigmentation of such 

 grafts is chiefly epidermal may be obtained by peeling off the 

 epidermis. Such removal, causing the disappearance of pigmen- 

 tation, is always followed by a regeneration of epidermis con- 

 taining melanophores. Belly skin grafted on to the tail becomes 

 pigmented in the same way. The parallel arrangement of the 

 melanophores, the concentration of the pigment cells along the 

 diagonals, and especially the presence of melanin granules 

 throughout the epidermis were features that were observed. 



2. Homoiotransplants 



Homoiotransplants of white skin on the back likewise became 

 pigmented, but the process was different in several respects. 

 From the six cases examined, the records of the following three 

 are of special interest : 



Graft LB 32 was taken from the belly of a large tadpole of R. clami- 

 tans (80 mm. long) and placed on the back of a small animal (52 mm. 

 long) of the same species. Twenty-four hours after the operation the 

 graft was pigmented. The melanophores were not numerous, and were 

 evenly distributed. Therefore the graft was only a trifle darker than 

 when it was placed. The parallel arrangement near the edges was 

 very prominent. Melanin granules and irregular masses of pigment 

 were not to be seen. At the end of twenty-eight hours the graft was 

 fixed for sectioning. The preparations showed the presence of melano- 

 phores in the slightly thickened epidermis. These were indications 

 that the epidermis had migrated from the surrounding skin carrying 

 with it melanophores. 



Grafts LB 35 and 36 were reciprocal: that is, belly skin from no. 35 

 was grafted to the back of no. 36, and bell}'- skin from no. 36 was grafted 

 to the back of no. 35. The animals were of the same appearance, 

 species, and size (45 mm. long). The histories of the pigmentation 

 process in these two grafts were alike. The vascular reaction was 



