OF THE KAGU, SUN-BITTERN, AND BOATBILL. 471 
So amply has the pterylosis generally of groups and many genera of the Wading 
Birds been worked out by Nitzsch that it would be superfluous in me to enlarge in 
comparisons. 
(6) Powder-downs, their Structure, Situation, and mode of Examination —Perhaps 
the most interesting point concerning the structural formation of the feathery covering 
of the birds under consideration, is that of the powder-down feathers (Puder- oder 
Staub-Dunen of Nitzsch, evidently the jlake-feathers of McGillivray’). Not only is 
their microscopic structure curious, but their physiological adaptation and use is as 
strange. 
Nitzsch arrived at the conclusion they are secretory organs; and, taken in a certain 
sense, this view appears to me quite justifiable. 
In their minute constituents I find Nitzsch’s observations to be very accurate, as far 
as they go; and I can further bear evidence to his asseveration that birds of widely 
different families possess them. The forms which I have more particulary studied have 
been those forming the basis of the present paper, several species of Bittern, Heron, 
Night-Heron, and Parrots, though I have not confined myself to these groups. 
The powder-patches in the different birds vary in their outward appearance and 
aggregate quantities, and moreover exist in several situations in the same bird. 
The best-known and most notable sort is that wherein they form the so-called 
“patches,” or are aggregated closely and terminate in a long free plume. Such, for 
instance, is the predominant character in the Herons generally, in Baleniceps, Lepto- 
soma, and, more excellently figured by Dr. Sclater* than in any case I know, in 
Podargus cuvieri, Vig. et Horsf., the woodcut of which I have been enabled to incor- 
porate in the text (wid. infra, p. 483). 
But the powder-down feathers, according to my researches, are far more freely dis. 
tributed than has hitherto been suspected, not so much in bunches as in the form of 
short roots or feather-sprouts, in great part wanting the free terminal plume so obvious 
where collected in masses. Indeed there would seem grounds for believing that the 
comparatively solitary short kind of powder-down feathers might represent a first stage 
of arrested down-feathers, whilst the plumose variety would be a second, erupted stage, 
the down-feathers themselves completing the gradation of growth. Of the so-called 
filoplume of Nitzsch, distinguished by their extraordinary slendemness, he himself 
incidentally notes, “To the latter I formerly gave the name of arrested feathers 
(Kiimmerfeder),” thus intimating, as it were, his idea of serial developmental grades 
existing between the different kinds of feathers. 
Regarding the distribution of the powder-downs, I shall treat of this at length as I. 
proceed, but propose first to inquire in what respects they are distinguishable from other 
portions of the plumage, and what constitutes these differences, textually. 
© A History of English Birds,’ vol. i. 
* “ Additional Notes on the Caprimulgide,” P. Z. 8. 1866, p. 581, fig. 1. 
