42 THE CLASSIFICATION OF BIKDS 



true, implies the independent acquirement of so extraordinary 

 a character as the loss of the fifth secondary, is almost startling 

 enough to shake one's faith in the laws of natural selection from 

 fortuitous variations. 



The Caprimulgidce are not found in Arctic climates, otherwise 

 they may be regarded as cosmopolitan ; the Podargidce are con- 

 fined to Papuasia and Australia ; and the Steatornithidce to South 

 America. 



18. PICARLE. 



The Picarise consist of half-a-dozen families, most of them 

 very nearly allied. The most aberrant appear to be the Cypsdidce 

 and the Coliidce. In all the other families the feet are syndactyle. 

 The Cypsdidce are further distinguished by being aegithognathous ; 

 all the other families are desmognathous. The Coliidce also differ 

 from all the other families in the pterylosis of their-underparts ; 

 they have no ventral bare tract. The Buccrotidce may perhaps 

 claim to be also aberrant, inasmuch as they have no lateral bare 

 tracts on the neck. As regards the pterylosis of the upper parts, 

 the Alcedinidcv, the Momotidce, and the Todidce are peculiar in being 

 typically passerine to the extent of having the dorsal feather-tract 

 well defined from the nape to the oil-gland by lateral bare tracts, 

 but not split by any dorsal bare tract. The Meropidce are pecu- 

 liar in having the episternal processes fused together anteriorly so 

 as to form a bridge over the feet of the coracoids. The Todidce 

 are peculiar in combining functional casca with a tufted oil-gland. 

 The Coraciidce agree with the Meropidce in combining functional 

 coaca with a nude oil-gland. The Alcedinidce, the Coliidce, and the 

 Bucerotidce have a tufted oil-gland, but no caeca. The Momotidce 

 and the Cypselidce have a nude or nearly nude oil-gland, and no 

 caaca. These characters are sufficient to diagnose all the families, 

 and leave the Coraciidce as the least specialised or most typical 

 group. 



The ranges of the Cypselidce and the Alcedinidce may be 

 regarded as almost cosmopolitan, but they do not extend to the 

 Arctic climates. The Coraciidce and the Meropidce are distributed 

 over the temperate and tropical parts of the Old World. The 

 Bucerotidce are more exclusively tropical, and are also unknown 

 in the New World ; the Coliidcc are very restricted in their range, 

 which is confined to Africa ; whilst the Momotidce and the Todidce 

 are only known from tropical America. 



