GENERAL ORNITHOLOGY 



particular names. A rectrix, broad to the very tip, and there cut 

 squarely off, is said to be truncate ; one such cut obliquely off is 

 incised, esj)ecially when, as often happens, the outline of the cut-oft' 

 is concave. A linear rectrix is very narrow, Avith parallel sides ; a 

 lanceolate one is broader at the base, thence tapering regularly and 

 gradually to the tip. A notably pointed rectrix is said to be axutc ; 

 when the pointing is produced by abrupt contraction near the tip, 

 as in most woodpeckers, the feather is acuminate. A very long and 

 slender, more or less linear feather is called filamentous, as the lateral 

 pair of a barn-swallow or most sea-swallows. The vanes sometimes 

 enlarge abruptly at the end, forming a spoon-shaped or spatulate 

 feather ; or such a spoon may result from narrowing of the vanes 

 near the end, or their entire absence, as in the " racket " of a saw- 

 bill (Momotus). The vanes are sometimes wavy as if crimped ; Plotus 

 is a fine example of this. Sometimes the vanes are entirely loosened, 

 the barbs being remote from each other, as in the exotic genus Stijn,- 

 turus, and some parts of the wonderful caudal appendage of the male 

 lyre-bird {Menura supcrha, Fig. 32). When the rhachis projects 

 beyond the vanes, the feather is spinose, or better, mucronate (Lat. 

 mucro, a pricker), as excellently shown in a chimney-swift of the genus 

 Chcetura. A pair of feathers abruptly extending far be3^ond the 

 others are called long-exseriecl, after the analogous use of the term in 

 botany. Tail-feathers also diff"er much in their consistency, from the 

 softest and weakest, not well distinguished from coverts, to such stiff' 

 and rugged props as the Avoodpeckers possess. They are downy and 

 very rudimentary in a few birds, notably all the grebes, Podicipedklce, 

 which are commonly said to have no tail. The tinamous of South 

 America (Drojnceognathce) are also very closely docked. The 



Typical Number of Reetriees is ttvelve. This holds in the 

 great majority of birds. It is so uniform throughout the great 

 group Oscines, that the rare exceptions seem perfectly anomalous. 

 In the other group of Passeres (Clainatores) it is usually twelve, 

 sometimes ten. Ten is the rule among Picarice, though many have 

 twelve, a very few only eight, as in the genus Crotophaga. The 

 whole of the woodpeckers (Picidce) have apparently ten ; but really 

 twelve, of which the outer one on each side is spurious, very small, 

 and hidden between the bases of the second and third feathers. 

 Birds of prey {Puiptores) have usually twelve. In pigeons the rule 

 is twelve or fourteen ; but sixteen are found in some, and twent}' 

 in one case. In birds below these, the number increases directly ; 

 there are often or usually more than twelve in the grouse famil}^, 

 and there may be sixteen, eighteen, or twenty, as among American 

 genera of Tetraonida'. Wading birds, often having but twelve, 

 furnish instances of as many as twenty. Those swimming birds 

 with large well-formed tails, as the Longipennes, and some Anatidm 



