Vol. XX" 

 1903 . 



Recent Lifci-ature. 



445 



^'marked ti-ans\erse or vertical element" is found to enter into the con- 

 ditions, and "this tians\erse arrangement is a survival, therefore," 

 according to the author, "of the phylogenetic affinities which link the 

 present Class Aves to their Saurian ancestrv." The great importance of 

 the wing-coverts in "helping to clear up outstanding questions connected 

 with the evolution of the organ of flight" has been fully reorganized bv 

 Pjcraft and Goodchild whose conclusions are here cited. 



Under the head of 'Conclusions ' is a long discussion of the exolution 

 of the wing of the modern bird, with regard to the original point of origin 

 of the flight-featliei-s. Ilis final conclusions are expi^essed in the fol- 

 lowing 



Revised Scheme for the Derivaton of the Flight-feathers 



FROM THE TeTRADACTVLE AnCESTRAL FoRM OF BiRDS. 



Proto-metacarpo-digitals = Hypo-metacarpo-digitals ^ 



Flight feathers of Phalangeal Origin. Flight feathers of Metacarpal Origin. 



Di<;iT I. 

 Suppressed (lost). Present PennK pollicis IV-I. 



Dl(,IT II. 

 Present Metacanw-digitals XI-VI. Present intercalary row I-VI. 



Digit III. 

 Present Metacarpo-digitals V-I. Present Cubital Group II, Secondary Reniiges (o) I-IV. 



Digit IV. 



Present Cubital Group III, Secon- Present Cubital Group I, .Secondary Remiges 



dary Remiges V-VII. VIII-X.— Cubiti veri Xl-r. 



Direction of ISIoiilt. 



(Left Wing.) 



"From the foregoing scheme it may be observed that there are no 

 flight-feather equivalents allotted to the phalangeal portion of Digit I, in 

 which part they figure as ' suppressed ' This tendency towards a part- 

 suppression, if carried further, would have the effect of leading to total 

 apoptilism. It, moreover, must have proceeded contemporaneously with 

 the feathering of the forearm and was still in progress after, as is evi- 

 denced in the Passeres, where it has reached the present climax in the 

 Oscines proper. 



"Considering the genealogical relative shortness of Digit I, coupled 

 with the fact of a still greater reduction of size in the present forms of 

 birds to one compound clement, there is strong probability existing that, 

 during the course of the fusion of the phalangeal segments of this digit 

 with its originally independent metacarpal bone, they were stripped off 



