206 



In this are divers little cells ending in two or three 

 large ones, lying under the nipple of the oil-bag. This 

 nipple is perforated, and being prest by the bird's bill, 

 emits its oil. 



In all birds that fly much, the \vings are placed in 

 the very best manner to balance their bodies in the air, 

 and to give as swift a progression as they are severally 

 capable of. Otherwise they would reel and fly un- 

 steadily, as we see they do if we destroy the equipoise 

 by cutting one of their wings. 



And what nicety may we observe, in a part no more 

 considerable, than the vanes of the flag.feathers of the 

 wing! 1. The edges of the exterior or narrow vanes 

 bend downward, but the interior, wider vanes upward, 

 By this means they catch hold and lie close to each 

 other, when the wing is spread, that not one feather 

 may miss its full force and impulse upon the air. 2. 

 Equal nicety is observed in the very sloping the tips 

 of the flag- feathers ; the interior vanes are neatly 

 sloped away to a point toward the outward part of the 

 wing. The exterior (at least in many birds) are sloped 

 toward the bcdy,. and in the middle of the wing, the 

 vanes being equal, are but little sloped ; so. that the 

 wing, whether open or shut, is as neatly sloped as if 

 constantly trimmed with a pair of scissars. 



The vane consists not of oye continued membrane, 

 because if once broken, it would not easily be repair, 

 ed ; but of many laminae, which are thin, stiff, and 

 something resembling a thin quill. Toward the shaft 

 of the feather (especially in the flag-feathers of the 

 wing) these laminae are broad and of a semicircular 

 form, which serves for strength and for shutting them 

 close together, when impulses are made on the air. 

 Toward the outer part of the vane, they grow slender 

 and taper, on their under side they are thin and 

 smooth, but their upper outer edge is parted into two 

 hairy edges. 



As curiously made are the feathers in the wing, and 

 no less curiously placed, exactly according to their se. 

 veral lengths and strength] aud these agaiu are lined} 



