36 THE BIOLOGY OF BIRDS 



some cases there is some indication of origin from the 

 hasmoglobin of the blood. 



Strong has shown (19 17) that the dark pigment or 

 melanin of birds' feathers has an epidermic origin in fowls 

 at least, and appears in epidermic parts of the feather-germ. 

 Some melanophore-cells also occur in the dermal pulp at 

 the lower end of the feather-germ, but these do not pass 

 into the feather. 



(3) The haemoglobin of the blood is a protein pigment, 

 containing iron. It occurs in all Vertebrates and in many 

 Invertebrates, and is of fundamental importance because 

 of its power of capturing oxygen from the atmosphere (in 

 the bird's lungs) and carrying it to the tissues. It is a good 

 example of a protein that can be readily got in crystalline 

 form (blood-crystals), though it never occurs in that form 

 in the living animal. Of great interest, as illustrating the 

 individuality of each species, is the fact that the form of 

 the blood crystals in nearly related mammals is different. 

 It is probably the same with birds, for specificity is a general 

 fact in regard to different kinds of living creatures. 



Haemoglobin gives origin to other pigments, such as 

 bilirubin — the reddish pigment of the bile, which in turn 

 is the mother-substance of others ; such as the green 

 biliverdin of the bile and the urobilin of the urine. 



(4) A number of peculiar pigments may be grouped 

 together. Very remarkable is turacin discovered by Church 

 (1869 and 1893) in the red feathers of the African family of 

 Plantain-Eaters (Musophagidae). It also occurs, according 

 to Krukenberg, in one of the Cuckoos, Dasylophus super- 

 ciliosus. It contains 5-8 per cent, of copper, as is indicated 

 by the green flame shown by the feathers when burnt. 

 The pigment is so soluble that it is washed out by the rain, 

 and when birds take a bath they colour the water red. 

 What is lost is of course replaced. Also in Plantain-Eaters 

 is turacoverdin, the only green pigment in birds, containing 

 iron but no copper. There are, of course, many instances 

 of green colour, but there is only this single occurrence of 

 green pigment ; and similarly it may be noted that while 



