346 BRITISH BIRDS. 



So far, I believe they are to be regarded as derived not 

 from down-feathers, but from contour-feathers. 



As to their function we are also completely in the dark. 

 According to some, these feathers, at any rate in the 

 Heron, are luminous, and are used by the bird as lures 

 when fishing by night ! Such a suggestion could, 

 obviously, come only from those who were unconversant 

 with the habits of the Heron and the number and position 

 of the supposed luminous areas. The assumption that 

 this "powder-down" possessed luminous properties has led 

 more than one writer, during the last few months, to 

 suggest that the luminosity exhibited by certain Barn- 

 Owls — to which reference has been made in this journal — 

 was similarly due to "powder-down" feathers. But these 

 are conspicuous by their absence in the Owls ! Another 

 suggestion is that the powder serves as a disinfectant. 

 Herons and Parrots, for example, being cited as instances 

 of birds which are devoid of external parasites as a 

 consequence of the powder which j)ermeates their plumage. 

 But the truth of this hypothesis has, so far, never been 

 seriously tested. At the time of writing I cannot recall 

 whether the Herons and Parrots are free from the usual 

 bird-lice (Mallophaga), but these swarm on Pigeons — at 

 any rate on domesticated pigeons — and few other birds 

 produce this powder in such abundance. 



The source and nature of this powder in the Pigeons I 

 am now endeavouring to discover, and I believe that in 

 these birds we shall find the earliest stages in the evolu- 

 tion of this remarkable phenomenon. The results of my 

 investigation I hope to lay before the readers of British 

 Birds at an early date. 



