FEATHERS OF BIRDS. 503 



those marked b, b, proceeding from the other side 

 of the lamina, or that nearest the root of the feather, 

 are shorter and firmer, and do not divide into 

 branches, but are hooked at the extremities, and 

 are directed upwards. When the two laminae are 

 brought close to one another, the long, curved 

 fibrils of the one being carried over the short and 

 straight fibrils of the other, both sets become en- 

 tangled together ; their crooked ends fastening into 

 one another, just as the latch of a door falls into the 

 cavity of the catch, which is fixed in the door-post 

 to receive it. The way in which this takes place 

 will be readily perceived by making a section of 

 the vane of a feather across the laminae, and ex- 

 amining with a good microscope their cut edges, 

 while they are gently separated from one another. 

 The appearance they then present is exhibited in 

 Fig. 227, which shows distinctly the form, direction, 

 and relative positions of each set of fibrils, and the 

 manner in which they lay hold of one another. 

 This mechanism is repeated over every part of the 

 feather, and constitutes a closely reticulated surface 

 of great extent, admirably calculated to prevent the 

 passage of the air through it, and to create by its 

 motion that degree of resistance which it is intended 

 the wing should encounter.* In feathers not in- 

 tended for liight, as in those of the ostrich, the 

 fibrils are altogether wanting : in those of the pea- 



* A very clear account of the mechanism described in the text is 

 given by Paley, in the 12th chapter of his " Natural Theology." 

 Many of the minuter details I have supplied from my own observa- 

 tions vv'ith the microscope. The branched form of the upper fibrils, 

 and the reticulated structure of the laminae themselves, when viewed 

 with a high magnifying power, are particularly beautiful microscopic 

 objects. 



