Leo Loeb and E. M. Strong 281 



farther into the underhjing fibrin; they never come from the underlying 

 tissue into the fibrin. Under these conditions they usually lose their 

 processes. Near such places the fibrin may be entirely free from con- 

 nective tissue. In some cases, taken at different times during the first 

 three weeks, the skin adjoining the wound was unequally pigmented, and 

 the regenerating epidermis often varied correspondingly in pigmentation. 

 On a side where the epithelium adjoining the wound was more heavily 

 pigmented, there were more chromatophores in the regenerating epider- 

 mis over the wound than at another place where the adjoining side was 

 less pigmented. 



instead of the common arrangement of pigment on the outer side of 

 the nucleus, which is characteristic of normal epithelial cells, we often 

 find an irregular arrangement of the pigment in the cells of regenerating 

 epithelium, which is probably due to the turning of the cells in the 

 movement over the wound. 



Chromatophores do not appear in the cutis until after two or three 

 weeks, though regeneration begins here at the end of five days. In fact, 

 the sub-epidermal part of the wound is filled with connective tissue before 

 any chromatophores are to be seen in it. 



It is therefore evident that the chromatophores of the regenerating 

 epidermis cannot possibly come from the regenerating dermis. Dermal 

 chromatophores are sometimes found at early periods, i. e., after the 

 fifth day, projecting slightly into the wound where they were probably 

 carried passively by the advancing fibroblasts. They remain, however, 

 near the margin of the wound. 



Occasionally we found small cells bearing pigment granules in the 

 fibrin or in the newly-formed connective tissue. They are leucocytes 

 or young connective-tissue cells. The chromatophores of the dermis were 

 not regularly arranged at the end of thirty-four days ; they were missing 

 at some places, and at other points they were situated deeper than is 

 the case normally. They appear, occasionally, in increased numbers at 

 the margin of the wound where they are sometimes surrounded by masses 

 of small round cells. 



In the experiments with wounds in tadpole skin, referred to previously 

 in this paper, the regenerating tissue was taken at periods varying from 

 a few hours to six days after the operation. The chromatophores of 

 both the epidermis and the cutis showed characteristics like those that 

 have just been described for the frog. 



In the case of transplanted guinea-pig skin, pigment is produced by 

 epidermal cells and is not directly the product of material carried to the 



