104 



SOME SUGGESTIONS FOR BIRD STUDY. 



B 



so-called inferior umbilicus). Within the quill can be 

 seen the shrunken pith. If a feather be carefully slit 

 along the quill this pith will be found to be arranged in a 

 series of cones overlapping each other (Fig. 25, 5). 



At the base of the vane will be found a few detached 

 straggling barbs. They are apt to be overlooked, or at 

 all events regarded as of no significance. But in some 

 feathers these form a definite second shaft with vane, 

 which is sometimes, e.g. in the Emu, as long as the main 

 feather. This is called the after- shaft. Note the after- 

 shaft of the Heron's covert shown in Fig. 25, 3. Other birds 

 which show the after- shaft clearly are Parrots and Gulls. 



We come now to 

 the vane or web. It 

 consists of a close-set 

 series of lateral rays 

 growing out from the 

 upper shaft. Let the 

 pupils discover exact- 

 ly from what part 

 these lateral rays 

 arise. They are 

 termed barbs (Fig. 

 28). Pupils will add 

 a set of barbs to their 

 drawing of the shaft, 

 filling them in at in- 

 tervals sufficient to 

 give the correct outline to the whole feather. Let them 

 examine the barbs closely, using a pocket lens if such is 

 available. They will note of course that in a quill feather 

 the barbs are not free, that in fact the adherence of the 

 barbs of the quill to each other is the property which 

 gives to the feather its effectiveness as an instrument for 

 striking the air in flight. 



A close examination shows that the barbs have them- 

 selves lateral offshoots, repeating the structure of the 

 main feather. Pupils will fill in these lateral offshoots on 

 some of the barbs in their drawing. How do these bar- 

 bules, as the secondary barbs are termed, adhere to each 



Pig. 28. Portion of a feather. 

 #, shaft ; B, barbs ; &, barbules. 



