INTRODUCTIOX. 
XXV i I 
are united in the way described ; evidently to oppose to the atmosphere a 
light and buoyant instrument, impermeable by it : while the other parts of 
the plumage of the animal, not having the same office to perform, are 
commonly composed of lamina, or rays, unconnected by hooks, and are 
distinguished by a peculiar fringiness, particularly in the different species of 
Titmice, in the body feathers of the Jay, the Nuthatch, and the Rail ; in 
the tufts around the external parts of the ear and the face of the Owl 
kinds ; but those that compose the brown-tipped circle, round the heads 
of the latter birds, are more closely woven, and more matted, even than the 
rays of the wings, and strikingly resemble the petals of the daisy. To 
repair the injuries which the plumage of birds sustains by continual use, a 
white, unctuous matter is secreted in a small gland, and sometimes in 
two glands, situated on the rump, at the top of which is a little apertory 
duct, through which the bird presses the oil with its bill, whenever its 
ruffled clothing requires repair. This gland, in many of the species is 
encircled by a small tuft of light, white feathers ; and when the bird wishes 
to preen itself, it begins with placing its plumage in order, and then by 
pressing its bill on the gland, extracts the oil, and rubs it over the surface 
of those feathers that have been injured. By this operation they are 
softened and more readily arranged. Water birds in general secrete a larger 
quantity of this useful oil than land birds, as their plumage requires it for 
a two-fold purpose, to make it more impervious to humidity, as well as to 
repair it. The rancid odour of the flesh of many water fowl is commu- 
nicated in a great measure by this oil, and the ill flavour is in some degree 
extinguished, by taking off the back-bone before they are dressed. The 
plumage of birds is neither of the same hues, nor brilliancy in the young, 
as in the old ; nor are those of the same species always clad in exactly 
similar colours. In general, it increases in splendour of colouring with the 
age of the bird. Some young birds are covered with feathers of colours 
so different from those of their parents, that an inattentive observer would 
The Puffin has two glands and Hvo apertory ducts. 
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