16 



EVENINGS AT THE MICROSCOPE. 



scope, we see that the central stem carries on each side a 

 row of barbs, which interlock with each other. The mag- 

 nifying power shows us that these barbs are not simple 

 filaments, but are themselves doubly bearded in the same 

 fashion ; and further, that these little beards, called bar- 

 bules, of the second series, are furnished with a third 

 series. It is in this third series of filaments, called bar- 

 bulets, that the tenacity in question resides. If we isolate 

 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 towards the point of the feather bear much 

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

 hooked backwards. Xow, whenever the primary beards 

 are brought into contact, some of these hooks catch on 

 the barbule next above, and, slipping into the angles 

 formed by the barbulets, hold there, and thus the two 

 contiguous beards are firmly locked together. 



In the beard of the goose-quill, 

 the structure is essentially the 

 same, but the barbulets are far 

 more numerous and more closely 

 set ; they are also proportionally 

 much larger — both those which 

 are hooked and those which are 

 simple. Indeed, the latter mani- 

 fest a tendency to the hooked 

 form, and by all these peculiari- 

 ties the interlocking power is aug- 

 mented. It is interesting to ob- 

 serve the great expansion of the 

 beard in a direction towards the 

 interior surface of the feather — 

 barb fbom GoosB-QiiLL. towards the stroke, as I just now 



