28 EVENINGS AT THE MICROSCOPE 



of the vane of a feather, and the exquisite manner in 

 which the beards of which it is composed are connected 

 together. This is specially observable in the wing- feathers 

 a goose- quill, for example; where the vane, though very 

 light and thin, forms an exceedingly firm resisting me- 

 dium, the individual beards maintaining their union with 

 great tenacity, and resuming it immediately, when they 

 have been violently separated. 



Now this property is of high importance in the econ- 

 omy of the bird. It is essential that with great lightness 

 and buoyancy for the bird is a flying creature there be 

 power to strike the air with a broad resisting surface. The 

 wide vanes of the quill- feathers afford these two requisites, 

 strength and lightness; the latter depending on the material 

 employed, which is very cellular, and the former on the 

 mode in which the individual barbs, set edgewise to the 

 direction of the stroke, take a firm hold on each other. 



Now, in the body-feather which is under the microscope 

 we see that the central stem carries on each side a row of 

 barbs, which interlock with each other. The magnifying 

 power shows us that these barbs are not simple filaments, 

 but are themselves doubly bearded in the same fashion; 

 and further, that these barbules of the second series are 

 furnished with a third series. It is in this third series of 

 filaments that the tenacity in question resides. If we iso- 

 late one of the primary beards, by stripping away a few on 

 each side of it, and again put it on the stage, we see that 

 the secondary barbules of one side are armed differently 

 from those of the other side. Those of the lower side carry 

 short and simple barbulets, whereas those of the side which 

 looks toward the point of the feather bear much longer 

 ones; and, moreover, many of them are abruptly hooked 



