126 COMPARATIVE ANATOMY. 



togetlier, strength and lightness. I know few things 

 more remarkable, than the strength and lightness of the 

 very pen, with which I am writing. If we cast our eye 

 to the upper part of the stem, we see a material, made for 

 the purpose, used in no other class of animals, and in no 

 other part of birds ; tough, light, pliant, elastic. The 

 pith, also, which feeds the feathers, is amongst animal 

 substances, sui generis ; neither bone, flesh, membrane, 

 nor tendon. 



But the artificial part of a feather is a heard, or, as it 

 is sometimes, I believe, called, the vane. By the Ijeards 

 are meant, what are fastened on each side of the stem, and 

 what constitute the breadth of the feather; what we usual- 

 ly strip off, from one side or both, when we make a pen. 

 The separate pieces, or laminae, of which the beard is 

 composed, are called threads, sometimes filaments, or rays. 

 Now the first thing which an attentive observer will remark 

 is, how much stronger the beard of the feather shows it- 

 self to be, when pressed in a direction perpendicular to its 

 plane, than when rubbed, either up or down, in the line of 

 the stem ; and he will soon discover the structure which 

 occasions this difference, viz. that the laminae whereof 

 these beards are composed, are flat^ and placed with their 

 flat sides towards each other ; by which means, whilst they 

 easily bend for the approaching of each other, as any one 

 may perceive by drawing his finger ever so lightly upwards, 

 they are much harder to bend out of their plane, which is 

 the direction in which they have to encounter the impulse 

 and pressure of the air ; and in which their strength is 

 wanted, and put to the trial. 



This is one particularity in the structure of a feather : 

 a second is still more extraordinary. Whoever examines 

 a feather, cannot help taking notice, that the threads or la- 

 minae of which we have been speaking, in their natural 

 state unite; that their union is something more than the 

 mere apposition of loose surfaces ; that they are not part- 

 ed asunder without some degree of force ; that nevertheless 

 there is no glutinous cohesion between them : that, there- 

 fore, by some mechanical .means or other, they catch or 

 clasp among themselves, thereby giving to the beard or 

 vane its closeness and compactness of texture. Nor is this 

 all : when two lamina?, which have been separated by acci- 

 dent or force, are brought together again, they immediately 

 redasp : the connexion, whatever it was, is perfectly re- 

 covered, and the beard of the feather becomes as smooth 



