MOEPHOLOGT OF THE OWLS 269 



that of tlie Capi-lmulgl and clitFevs froiu the Accipiti-es iu that it is appareutiy com^oosed 

 entirely of pre-pennce, whilst that of the Acclpiires is a mixture of pre-pennce and 

 pre-plumidcB. As a piece of additional evidence in favour of Dr. Gadow's position, I 

 would draw attention to the linear, transversely oljlique, arrangement of the dorsal 

 tectrices of the w^ini;-, which in this particu.lar agree with the Capnmulgi. 



It seems evident that, in endeavouring to trace out the origin and Hues of descent of 

 any given group of birds, we can no more trust the evidence of pterylosis alone than that 

 of any of the other systems or organs that have from time to time been pressed into 

 service to this end, but that, judiciously combined with other characters, it Avill afford 

 help of some value. As an instrument for defining species it is possible that it may prove 

 a more reliable weapon, but this yet remains to be seen. It would be interesting to apply 

 this test to the examination of some of the reputed species and subspecies, or, as some 

 would have it, varieties of the Barn Owl, and see wliether or not the superficial differences 

 were accompanied by corresponding differences in the distribution of the feathers. 



Key to the Families, Sifb-families, and Genera. 



A. The median branch of tlie ventral tract free posteriorly ; the feathers of the hinder 

 border of the acrotarsiuni directed downwards ; no filoplumes at the end of the 

 oil-gland I. Asionid^. 



a. Interscapular region of the pt. spinalis with a lon;^- bifurcation . . . Sub-fam. 1. AsionincB. 

 a'. Height of vertical axis of the external aperture of the ear three times that 



of the horizontal axis of the eyelid. 

 a". Preaural and postaural folds voluminous, the former constituting an 



operculum, which is provided with a valve; oil-gland napiform .... 1. Asiu. 

 b'. Height of the vertical axis of the exterual aperture of the car never exceeding 

 that of the horizontal axis of the eyelid; preaural fold not forming an operculum. 

 //'. Oil-gland conical ; cere not inflated, but closely investing the base of the 



beak ; posterior division of the cavernum confined to its lower half ... 2. Bubo, 

 c". Cere laterally inflated, posterior division of the cavernum extending its whole [ 3. Scops. 



vertical height 4. Ninox. 



c. Vertical axis of the external aperture of the ear uot exceeding that of the hori- [ 5. Sceloglaux. 

 zontal axis of the eyehd ; preaural fold forming an operculum, the free edge 

 of which overlaps that of tlie pustaural fold. 

 d". Posterior division of the cavernum confined to its lower third ; peripheral 

 disc-feathers meeting in the middle line near the symphysis of the mandible ; 

 inner branch of the pt. ventralis arising over the region of the head of the 

 coracoid 6. Syrnium. 



b. Interscapular region of the pt. .spinalis with a short bifurcation .... Sub-fam. 2. NyctalincB. 

 d' . Vertical axis of the external aperture of the ear twice that of the horizontal axis 



of the eyelid ; pre- and postaural folds moderately well developed. 



e". Cere short ; nostrils seated in pisiform inflations 7. Nyctala. 



e . Vertical axis of the external aperture of the ear equal to that of the hori- 

 zontal axis of the eyelid ; no operculum ; cavernum divisible into anterior and 

 posterior portions. 

 J". Tail long and pointed ; oil-gland napiform 8. Surnia. 



