404 WILLIAM H. COLE 



In the second place, the persistence of melanophores in a 

 region which is normally transparent and free from pigment cells 

 shows that a profound change has occurred in the integument, 

 or in the eye, since the time of early development. It was 

 pointed out earlier in this paper that at a certain stage in the 

 development of the eye the overlying ectoderm is thinned, loses 

 its pigment, and becomes transparent. If the ectoderm is re- 

 moved, the regenerated layer will become transparent, or if it 

 is replaced by ectoderm from another region, transparency will 

 be produced. Lewis ('05) speaks of this process as 'corneal 

 clearing.' However, if the eye is removed entirely previous to 

 this time, no such reaction of the ectoderm occurs. A definite 

 influence of the eye structure upon the ectoderm is thus demon- 

 strated. Since at a much later time pigment is tolerated in this 

 region, proof is obtained that either the eye has lost its power to 

 exert its stimulus upon the overlying skin or else the skin is 

 unable to respond to such a stimulus — a conclusion reached from 

 the study of the skin grafts over the eye. Another set of grafts 

 showed that in the different regions of the body the integument 

 is specific, having lost its embryonic totipotence. The condi- 

 tions found in the conjunctiva support these conclusions. The 

 tissue of the conjunctiva is specific also, but when it is badly 

 injured, the repair of the wound must be made by the surrounding 

 skin. The cells of that tissue are specific, and when they form 

 a new covering for the eye, they will retain their specificity. 

 Pigment cells which have been carried along will persist, and new 

 ones will be formed as in the normal growth activity of the -integ- 

 ument. There are better reasons to believe, therefore, that the 

 skin has lost its power to respond to the stimulus arising from the 

 eye, although the possibility that the eye exerts no stimulus upon 

 the skin is not excluded. 



Finally, the pigmentation of the conjunctiva resulting from an 

 injury recalls the appearance of pigment in regions of hyper- 

 trophy. There are several kinds of cancers in which the produc- 

 tion of pigment is very marked. Some of them are called mela- 

 notic because of excessive pigment production. In a study of the 

 origin of cancers, it has been shown that chronic inflammation 



