" QUINTOCUBITALISM " IN THE WING OF BIRDS. 213 



fully-developed secondary quills. Iq Golumbula picui there are 

 ten primaries aud also twelve fully-developed secondaries. In 

 Starnoe.nas cyanocephala (PL 13. fig. 6) there are ten primaries, 

 then an unusually large carpal remex with the normal binding 

 fold and covered by a small carpal covert ; then follow twelve 

 fully-developed secondaries without any trace of the diastataxic 

 ■gap. In PJilogoenas cruentata there are nine primaries, then a 

 normal covert and remex, then twelve fully- formed secondaries, 

 with no trace of the gap. 



It appears, then, that the Columbae form an interesting addition 

 to Kingfishers and Swifts, some members of which groups exhibit 

 fhe one condition, others the other ; and it is among such groups 

 that we may hope to find an explanation of the divergence in 

 structure *. The mere statement of the facts as they occur among 

 the Columbae seems to me at once to suggest an extremely prob- 

 able explanation. In most pigeons the wing is diastataxic, 

 with a large gap occupied by a " covert." In some pigeons 

 '(e. g. CEna and Geotrygon) there is practically no gap but a 

 covert crowded into the interspace which forms the gap in most 

 pigeons ; in Geopelia cuneata and G. tranquilla, in Columbula, 

 Leucosarcia, Starnoenas, Geopliaps, and JBhlogoenas there is no 

 gap, and there is apparently no extra covert. 



It is BOW necessary to consider a third row of feathers, for 

 simplicity not represented in the figures in the Plates, but shown 

 in fig. 1 in the text. Lying apparently iu between the quills 

 and coverts, but really belonging to a more dorsal series, there 

 is a small feather marked 3 in the figure ; except in the 

 gap marked x there is plenty of room for these third-series 

 feathers. In the gap, even in a diastataxic bird (fig. 1, 1), there 

 is a certain crowding of these feathers, which are rather smaller 

 than the others of their series. In a diastataxic bird where 

 there is no actual gap, as in CEna or Geotrygon (fig. 1, II), the 

 two feathers on either side of the actual covert are exceedingly 

 crowded, and are markedly degenerate, relatively much more so 

 than in the diagram, while the covert itself is smaller in size. 

 In the eutaxic birds (fig. 1, III) there is only one feather in this 

 interspace ; as a result the interspace does not difier from the 

 other interspaces. Which of the three crowded feathers has 

 remained I cannot be certain, but I think it probable that it is 



* The late Mr. Seebohm made the suggestion that eutaxic species may 

 rpossibly have arisen from diastataxic ancestors by suppression of the coverts 

 .{Classification of Birds, 1895, Suppl. p. 8). 



