164 bulletin: museum of comparative zoology. 



on them. I have had material in alcohol for months without any 

 apparent effect on melanin granules. It is not inconceivable that 

 histological re-agents may produce chemical changes in the developing 

 melanin granules, but I have had no positive evidence of any such 

 alterations. 



Especially to bo noticed is the red pigment turacin, which was 

 described by Church (*69, '93) as containing 7.1% of copper. Feathers 

 containing this pigment are said to give a red color to water in which 

 they may be placed. At the same time, there is more or less of a 

 tendency for such feathers to exchange their normal red color for blue ; 

 but the red returns when the feather is dried. Church found turacin 

 easily soluble in water, especially if the latter was slightly alkaline. 



B. The Origin of Pigment. 



The many writers on the origin of pigment in epidermal structures 

 may be divided into two groups : (1) those believing in an exogenoi^s 

 formation of pigment, and (2) those who argue for an endogenous or 

 autocthonous development of pigment in the epidermis. 



The theories ascribing an exogenous origin to pigment all involve a 

 more or less direct relation of pigment to the blood. Most prominent 

 is that which derives the melanins from the haematin of the red blood 

 corpuscles. Certain writers have argued that pigment originates in 

 internal organs, from which it is transported to the integument either 

 in solution in the blood plasma or as a colorless mother substance in 

 the blood-cells. Closely allied to this is the excretion- (or waste-) 

 product theory advocated by Eisig ('87) and others for invertebrates. 

 Finally, there is the leucocyte theory, which makes leucocytes the 

 bearers of pigment from the blood to the epidermis. 



The writers who have argued for an endogenous formation of pigment 

 in the epidermis believe that pigment results from the metabolic 

 activity of either the nucleus or the cytoplasm of epitlielial cells. 



Among those who have advocated an exogenous origin of the pigment 

 of epidermal structures are Langhans ('70), Gussenbauer ('75), Kerbert 

 ("76), Riehl ('84;, Aeby ('85), Quincke (,'85), Ehrmann ("83, "91, '92), 

 Kolliker ('87), Karg ('88), Phillipson ('90), Kaposi ('91), and Bloch ('97). 



The following have supported tlie endogenous origin : Demii^ville ('80), 

 Krukenberg ('84), Mertsching ('89), Jarisch ('91, '92), Kabl ('94), 

 Post ('94), Rosenstadt ('97), Loeb ('98), and Prowazek (:00). 



Pigment may be present either, (1) in the dermis only, (2) in the 



