28 



themselves ; these are destined not only to keep the adjacent barbs 

 together, but to rise above the outer surface of the vane, and so form 

 a kind of nap or down upon this surface. If we now compare one 

 of these feathers with one from the wing of a goose or any diurnal 

 bird of prey, the difference in structure between them will be very 

 manifest ; the one presents a surface perfectly level and smooth, whilst 

 the other is covered with down, formed, as has been before stated, by 

 the projection of the barbulettes above the outer surface. On the 

 inner side of the feather the barbulettes do not rise above the level of 

 the barbs, but on this inner surface the feathers of the owl tribe do 

 not differ from those of other birds. It is on the outer surface only 

 where the peculiarity above spoken of is to be found, the object of 

 such structure evidently being for the purpose of rendering their flight 

 perfectly noiseless. 



Of all the many complicated problems presented to us in Nature's 

 works, in none, perhaps, can we at once perceive more contrivance and 

 design than in the construction of this part of the feather, and in none 

 in which such problem will admit of so satisfactory a solution as the 

 subject under consideration. Owls, it is generally known, go abroad 

 at twilight, and their food consists principally of rats and mice, which, 

 like the owls themselves, go abroad in the evening in search of 

 food. Had owls the stiff and unyielding wing-feathers similar to 

 those with which diurnal birds of prey are provided which depend 

 upon the rapidity of their flight for the successful capture of their 

 prey, the noise necessarily made in the act of flying would disturb the 

 little animals in their repast, and they would be enabled to escape to 

 their hiding places before they could be pounced upon by their un- 

 suspected enemy. 



EXPLANATION OF PART OF PLATE II. 



Fig. 1. A portion of the vane of a wing-feather of an owl (Bubo maximus), magnified 



175 diameters, a, a, The barhulettes. 

 Fig. 2. A barb from the same vane of the natural size. 

 Fig. 3. A portion of one of the barbs magnified 175 diameters, shewing the barbules, 



a, and the barbulettes, b. 

 Fig. 4. A portion of a barb of a wing-feather of the crowned pigeon (Columba coro- 



nata), showing tbe barbules, a. 



