MOKPHOLOGY OF THE OAVLS. 225 



lengths of the primaries and the amount of the emargination of their inner vanes. In 

 Speolyto, save for the spinal tract, he tells us that " the pterylosis differs in no respect 

 from that described for S. bubo.'" 



In the Barn Owls the ventral tract is said to " agree precisely with that of Cathartes, 

 only differiug in that, in Utjhris { = Slria; Jlammea), the contour- feathers are more 

 numerous aud stand closer together." He was the first to draw attention to " two 

 minute feathers seated at the apex of the oil-gland." 



The Ibrin and nature of the facial disc are very carefully described, but he does not seem 

 to fully apj)reciate the difierenciis in the form of the external aperture of the ear and of 

 the opercular fold in the various Owls. 



I have been unable to confirm his description of the disc-feathers of S. otiis { — Asio 

 otus). According to him, " they consist of a large tube perfectly open above, upon which 

 a very small, sparsely-barbed shait is seated." 



As will be seen later, my own investigations bear out the main conclusions of Nitzsch's 

 work most completely. The wonder is that he failed to notice the numerous small but 

 very real ditiercnces by w^hich not only genera but even species may be distinguished. 

 It is also a matter for some surprise to find liim so closely associating Syrnium and Scops, 

 the pterylosis of which is said to be "as in Bubo.'' The resemblance between Bubo and 

 Scops is undoubtedly very great, as he indicates, but Sp'uium can be very readily 

 distinguished from either. 



It is somewhat strange to find that Kaup (8), in his " Monograph of the Strigidse," 

 published in the Trans. Zool. Soc. 1862, makes no mention of Nitzsch's work. He takes 

 into account only such facts as the presence or absence of '• horns," the form of the disc 

 — which he divides into a central " veil " surrounded by a " wreath," — the length of the 

 primary remiges, and whether or not they are eniarginate, and the presence or absence 

 of featiiers on the acrotarsium and acropodium. He draws attention to the fact that the 

 feathers seated in the posterior membranous fold surrounding the external aperture of 

 the ear are so arranged as to slope in opposite directions, meeting at an obtuse angle. 

 The feathers in the upper half of the fold are directed downwards, those in the lower 

 half are directed upwards. The feathers in this fold constitute the " wreath." 



Besides these, he also employed such external features as the form of the nostrils, the 

 development of the " cere," and the size of the external aperture of the ear. The points 

 noticed in the latter were (1) the size, measured with relation to the long axis of the 

 eyelids, its symmetry or asymmetry, and (2) the presence or absence of an operculum 

 or " anterior ear-lap " and of a posterior or " hinder ear-lap." The somewhat com- 

 plicated relations which, obtain in the asymmetrical ear-apertm*es of Asio are fairly 

 well described. 



The systematic arrangement resulting from his labours *, however, is decidedly inferior 

 to that of A'itzsch. He divided the Owls into two subfamilies, Syrniinse aud Striginse. 



* The osteology of the skull also found a place in his diagnoses. He employed such characters as the form of tho 

 occipital region and the pncumaticity of the bones. He was, I believe, the first to point out the swollen spongy 

 nature of the interorbital septum of the Barn Owl. 



31* 



