196 BRITISH BIRDS. 



Family PASSERIDiE, or SINGING BIRDS. 



The Singing Birds^ together with three other families* (o£ which there 

 are no representatives in Europe) ^ constitute what are frequently called 

 the true Passeres, the great central group of dominant birds — by far the 

 most numerous in genera and species^ yet exhibiting few anatomical 

 differences inter se — the most highly developed, and yet at the same time 

 the most cosmopolitan of birds. They may indeed be said to be absolutely 

 cosmopolitan, being found throughout the world, except on such rocky 

 coasts where no bird can exist which does not obtain its food from the 

 water. 



The Passeres are the typical birds, the great central apex of the genea- 

 logical tree, very nearly related to each other, and surrounded by outlying 

 families or branches much more distantly related, and consequently pre- 

 senting important anatomical characters by which to separate them from 

 the great central group and from each other. 



The Passeres are the true Aves ; the other families are the failures, the 

 least developed descendants of the intermediate forms which once connected 

 Birds and Reptiles, families containing comparatively few genera and 

 species, some fast dying out, but so widely separated from each other that 

 to trace their relationship we should have to go back almost to the roots 

 of the genealogical tree. So obscure indeed is this connexion that orni- 

 thologists cannot decide in some cases (the so-called Ratitcs, for instance) 

 whether they form one family or great group, or are the remnants of 

 several distantly connected groups. 



The Passerida are separated from the other three families to which 

 they are most nearly allied by a peculiar structure of the singing-appa- 

 ratus at the lower end of the windpipe; but this apparently exhausts 

 the anatomical characters which our physiologists have been able to discover, 

 and leaves us with nearly half the known species of birds so closely 

 related to each other that no known internal characters exist by which 

 they may be subdivided. 



* Sclater (Ibis, 1880, p. 34-5) divides his order Passeres into four suborders : — Oscines, 

 comprising about 4550 species (nearly half the species of birds known), principally found 

 in the Old World, but many peculiar to the New ; Oligomyodce, comprising about 550 

 species, principally found in the New World, but some peculiar to the Old ; Tracheophona?, 

 comprising ahout 500 species confined to tlie New World ; and Pseiidoscines, comprising 

 half a dozen sjeoies confined to Australia. 



