SKIN TRANSPLANTATION IN FROG TADPOLES 407 



2. In autotransplants the acquisition is chiefly the result of 

 formation of pigment from epithelial cells in situ. 



3. In homoiotransplants the pigmentation is chiefly the result 

 of epidermal migration which carries along the melanophores 

 from the surrounding skin. It is followed later by formation of 

 pigment in situ, as in the normal growth activity of integument. 



D. Pigmentation of the conjunctiva caused by injury 



1. When the conjunctiva of frog tadpoles is extensively injured 

 by scratching or pricking, the regenerated tissue is pigmented, 

 first by epidermal melanophores and later by dermal melano- 

 phores and xantholeucophores. 



2. The persistence of such pigmentation in the conjunctiva is 

 further proof that no correlation between the eye and the over- 

 lying integument exists in tadpoles 20 mm. or more in length. 



3. The epidermal melanophores are carried along by the mi- 

 grating epidermis. The second step in the pigmentation process 

 is probably a mitotic multiplication of integumentary cells, in- 

 cluding the formation of pigment cells, and is the result of the 

 normal growth activity of the integument. 



E. Reactions of the melanophores 



1. Expansion of the dermal melanophores is caused by a low 

 temperature (near 0°C.) independently of illumination, by dark- 

 ness, by a 0.1 per cent chloretone solution, by anoxemia, and by 

 the low metabolic rate of the whole animal coincident with a 

 moribund state. 



2. Contraction of the dermal melanophores is caused by a high 

 temperature (near 35°C.) independently of illumination, by light, 

 and by a return of normal environmental conditions after the re- 

 moval of the effects of chloretone and anoxemia. Contraction is 

 also coincident with the recovery from a moribund state. 



3 . Either expansion or contraction usually requires about thirty- 

 six hours for completion, although the reactions begin within 

 twenty minutes after the initiation of the stimulus. Oxygen de- 

 ficiency brings about complete expansion in about one-half hour. 



