414 THE OWLS 



border of this skin- fold is beset by long, closely planted, curved 

 feathers, framing in the disc which is borne by the outer surface of 

 the operculum. Has this remarkable modification of the ear aperture 

 anything to do with the detection of sound ? And what is the 

 significance of the changed position of the meatus, in regard to the 

 pulley from the operculum, in the two sides of the head ? In the 

 barn-owl the meatus opens relatively higher up than in the other 

 species so far mentioned, and is relatively small in size. But it is 

 also protected by an operculum which is much larger than the aper- 

 ture it covers. As in the genus Otus, long, stiff, curved feathers, closely 

 packed, run from above the eye backwards, downwards, and forwards 

 along the base of the lower jaw to form a more or less tubular ear- 

 trumpet, but in this case the feathers are not set in the free edge of 

 a broad rim of skin as in Otus, as may be seen by comparing Figs. 

 1 and 4. Finally, we come to Tengmalm's owl. So far asymmetry, 

 when it occurs, does not extend to the skull. But in NyctcHa the 

 skull itself is strangely changed in the region of the ear ; for on the 

 right side of the skull the post-orbital process forms a broad lobe 

 extending forwards to the eyeball, while on the left side of the head 

 the skull-wall is deeply notched. (Figs. 5 and 6.) So far no observa- 

 tions have been made on the habits of the living bird in this species 

 or in any others mentioned in this connection which enables one to 

 grasp what purpose these curious structural modifications may serve. 

 Embryology, so far, has thrown no light on the matter. But 

 some years ago 1 I examined an embryo longeared-owl, and in this 

 the aperture of the ear was like that of Scops that is to say, it was 

 a large aperture, but showed no sign of an operculum. 



1 Pycraft, "Morphology of the Owls," Trans. Linn. Soc., 1898. 



