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 be 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 coler 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 exogenous 
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 epithelial 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), 
Kélliker (87), Karg (88), Phillipson (90), Kaposi (91), and Bloch (’97). 
The following have supported the endogenous origin: Demiéville (’80), 
Krukenberg (84), Mertsching (89), Jarisch (91, ’92), Rabl (’94), 
Post (94), Rosenstadt (’97), Loeb (’98), and Prowazek (:00). 
Pigment may be present either, (1) in the dermis only, (2) in the 
