PKOOIS OJ^^ OKGANiSi^'G Aili\D 311 



that ^vhicli most clearly implies the working out of a j^recon- 

 ceived design in a new and apparently most complex and dilli- 

 cult manner, yet so as to produce a marvellously successful re- 

 sult. The idea worked out was to reduce the jointed bony 

 framework of the wings to a compact minimum of size and 

 maximum of strength in proportion to the muscular power 

 employed ; to enlarge the breastbone so as to give room for 

 greatly increased power of pectoral muscles; and to construct 

 that part of the wing used in flight in sucli a manner as to 

 combine great strength with extreme lightness and the most 

 perfect flexibility. In order to produce this more perfect in- 

 strument for flight the plan of a continuous membrane, as in 

 the flying reptiles (whose origin was probably contcm})ora- 

 neous with that of the earliest birds) and flying mammals, to 

 be developed at a much later period, was rejected, and its placo 

 was taken by a series of broad overlapping oars or vanes, 

 formed by a central rib of extreme strength, elasticity, and 

 lightness, with a web on each side made up of myriads of parts 

 or outgrowth so wonderfully attached and interlocked as to 

 form a self-supporting, highly elastic structure of almost in- 

 conceivable delicacy, very easily pierced or ruptured by the 

 impact of solid substances, yet able to sustain almost any 

 amount of air-pressure without injury. And even when any 

 part of this delicate web is injured by separating the adjacent 

 barbs from each other, they are so wonderfully constructed that 

 the pressure and movement of other feathers over them causes 

 them to unite together as firmly as before ; and this is done 

 not by any process of gro^vth, or by any adhesive exudation, 

 but by the mechanical structure of the delicate hooked lamelhn 

 of which they are composed. 



The two illustrations here given (Figs. lOS, lOD) show two 

 of the adjacent fibre-like parts (barbs) of which the web of a 

 bird's feather is composed, and which are most clearly shown 

 in the wing-feathers. Tlie slender barbs or ribs of which the 

 web of the feather is made up can be best understood by strip- 

 ping off a portion of the wel) and separating two of the barbs 



