THE LIFE-HISTORY OF BIRDS 



26s 



The Long and Short-eared Owls furnish yet another illus- 

 tration of the recapitulation theory, since in the adult the ears 

 of these birds differ in a most remarkable way from those of 

 all other Owls — or indeed of all other birds — while the em- 

 bryonic ear differs in no way from those of, say, the Eagle Owls, 

 which are normal. The young Cassowary furnishes a similar 



bristle sheath plug 



III. 30 



A, Dissection of tlie beak-sheath of a Cormorant showing the last trace of 

 the once open narial aperture — a bristle has been passed through to the opening 

 in the roof of the mouth. During life this aperture is closed by a plug, formed 

 by an ingrowth of the bony sheath. In the Embryo (B) the aperture is still open. 



example at a later stage of development. This we find in the 

 history of the growth of the curious spine-like quills of the 

 wing. In the nestling these resemble the less degenerate quills 

 of the Apteryx, having ^ distinct quill and vexillum : later this 

 latter portion is shed while the lower portion, or quill, increases 

 enormously in length, and becomes solid, forming some five or 



