12 STRUCTURE A^D CLASSIFICATION OF BIRDS 



and fully-sized in Nothura. It is occasionally present but 

 small, and sometimes even with its covert altogether absent. 

 The remiges themselves vary in number apart from the 

 presence or absence of the fifth cubital, but not within 

 very wide limits. Struthio and the penguin alone are 

 exceptional, and will be treated of separately and later. 

 Gadow has published a useful table showing the number of 

 the primaries in a very large assortment of birds belonging 

 to all orders. The number of primaries varies only between 

 ten and twelve. The number of metacarpals has also a 

 small range of variation, the smallest number presenting 

 six and the largest eight. Casuarius having an abbreviated 

 , hand is still further reduced, the primaries being only two 

 and the secondaries five. The largest number of metacarpals, 

 eight, is possessed, however, by Apteryx, with an abbreviated 

 hand, and by Struthio. Seven metacarpals are found in the 

 grebes, flamingoes, and several, but not all, the genera of 

 storks. All other birds have six. 



The two prominent exceptions to the foregoing state- 

 ments are, as has been already mentioned, Struthio and' the 

 Spheniscidee. In the ostrich (see fig. 3) there are sixteen 

 primaries, each with its tectrix major upon the upper surface 

 of the wing. The other rows are perfectly recognisable, as is 

 shown in the figure. The wing of the penguin is, however, 

 not reconcilable with the ordinary plan of structure. It has 

 thirty-six bordering feathers, which may be termed primaries ; 

 FxJRBRiNGEE has Suggested that these may be really ten 

 primaries with their coverts, but in any case the wing is 

 covered with about thirty rows of scale-like feathers. 



As to the general wing feathering, Goodchild ' has sur- 

 veyed a large series of birds, and noted their peculiarities. 

 Some valuable classificatory results appear to be the outcome 

 of these investigations. Thus the plan characteristic of the 

 humming birds resembles that of the swifts, and both are to 

 be distinguished from the passerines. The picarian type 

 gradually approx;imates to the psittacine ; Melopsittacus 



' ' Observations on the Disposition at the Cubital Coverts in Birds,' P. Z. S. 

 1886, p. 184. 



