HAIRS, FEATHERS, AND SCALES 31 



the current passing over each tile is deposited from its bot-_ 

 tom edge on the middle of the next one, whence it still flows 

 down to the free edge of this one, and so in succession. So 

 the motion of the bird through the air, and of the fish 

 through the water, produces the very same effect as if these 

 fluids were in motion and the animals were still; and there- 

 fore the bodies of the latter are, as it were, tiled with feath- 

 ers or scales, the free edges of which, looking in the oppo- 

 site direction to the coming of the current (that is, the same 

 direction as its flow), deposit the successive particles of the 

 moving fluid in the midst of the successive feathers or scales. 

 Thus two results ensue, both essential to the comfort of the 

 animal: first, the air or water does not run upward between 

 the feathers or scales to the skin; and, secondly, the stir- 

 face presents no impediment to free motion. This latter 

 advantage will be appreciated, if you take hold of a dead 

 bird by the legs, and push it rapidly through the air tail- 

 foremost: the feathers will instantly rise and ruffle up, 

 presenting a powerful resistance to movement in that 

 direction. 



These scales of the Perch have their hinder, or free 

 edge, set with fine crystalline points, arranged in succes- 

 sive rows, and overlapping. Their front side is cut with 

 a scalloped pattern, the extremities of undulations of the 

 surface that radiate from a common point behind the cen- 

 tre. These undulations are separated by narrow furrows, 

 across which, contrary to the ordinary rule, the close-set 

 concentric lines that follow the sinuosities of the outline 

 are not visible. Under the microscope they look as if they 

 had been split in these radiating lines, after the whole num- 

 ber of layers had been completed, and the fissures had then 

 been filled with new transparent substance. 



