•304 Proceedings of the Royal Irhh Academy. 



fat is red, in conjunction Tvitli a con'esponding external colouration of 

 the legs and bill. It has been sbown tbat for tbe Mamingo intensity 

 of tbe red colour is proportional to tbe amount of fat or oil present in 

 the feathers. 



Again, fat saturated ^ivitb pigment may be found in bii'ds whose 

 feathers are deeply pigmented, yet whose colours are not necessarily 

 red or yellow. Such are the Coot and Blackbird, the latter of which, 

 as Dr. G-adow informs me, may be distinguished in this very particular 

 from the closely allied but less darkly coloured Song-thrush. In the 

 Sacred Ibis, a white bird with the bUl, bare head and neck, and the 

 legs of the deepest black, the fat is intensely red. 



I further observed that the feather-tracts are amongst the parts of 

 the body where fat especially tends to accumulate. 



But deeply coloured fat is not confined to birds. It occurs also in 

 mammals, as is well known in the case of domestic cattle. I found it 

 ■also in wild forms, such as the South African Hedgehog and the Aard 

 "Wolf. It is present in abundance in reptiles, such as the African 

 ^Monitor, and in the Lizard Agaraa distanfi. In the Monitor and many 

 other reptiles, in which the fat is deeply pigmented, there is a strong 

 accumulation of black pigment ia the body cavity. Lastly, the 

 common Salmon is an instance of the same thing amongst fish. 



In all these creatures fat is frequently deposited in the ovaries, 

 testes, or other glands, which, as a result, are often yellow, sometimes 

 black, and to a similar cause the yolks of the eggs of birds owe their 

 colour. The yellow pigment of the yolks of fowl's eggs, called 

 by Kmkenberg coriosulf erin, is said to be, like zoomelanin, a coloured 

 fatty oil. 



The yellow or red fat pigments belong to the same class, that of 

 the Hpochromes, as the reds and yellows of external pigmentation. 

 They are also found in certain vegetable substances, such as maize. 

 If an animal be fed on maize, the colour of its fat is greatly heightened. 

 A third important pigment, but a little less intimately connected with 

 fat, is black. The constituents of the two are very similar, zoomelanin 

 being, according to Bogdanow, composed of carbon, hydrogen, 

 nitrogen, and oxygen, as found in the black feathers of Pica, Corvm, 

 and Ciconia. 



When we regard mammals and birds, we find, with few exceptions, 

 great uniformity of pigment-colours. Black, red, and yellow, with 

 their inter-mixtures, are almost the only three pigmentary colours 

 with which we have to deal. In the lower vertebrates the effect of 

 white is due also to a pigment, guanin, a purely waste product of 



