508 



NATURAL HISTORY OF BIRDS. 



gape split to near the eyes, but without bristles. Altogether thej- resemble closely 

 the swifts (Micropodida;), though structurally they are very different, and the distin- 

 guishing marks have already been jiointed out (ef. jiage 437). Jiiter xe, the different 

 species of swallows vary but very little, and no intermediate forms are known which 

 directly connect them with some other family, or indicate their line of descent. But 

 different as they ajipear externally from other Passeres, nothing is found inteniallv or 

 even in their ]iterylogra]ihy that will justify their being far removed from the forms 

 hitherto treated of. Says Professor W. K. Parker : " In this remarkable group of 

 tender-billed gaping Passeres, there is not, as far as 1 am aware, a single aberrant 



FlO. 249. — Clivicola riparin, bank-swallovr ; I'royiu: subis, purplc-inui tJu. 



character of inijioitance. The skull, the skeleton generally, the digestive and the 

 vocal organs — all these might !)elong to species of the genus Sj/lri<i." 



About one hundred species of swallows are recognized, distributed all over the 

 earth except the very arctic and antarctic regions. Uniform as is their structure, so 

 arc also their habits, they being cliielly migratory, and feeding on flying insects which 

 they catch on the wing. Their whole organization aims at great speed, aiul they spend 

 the greater jiart of their life in the air, but rarely i)crching in order to rest. The 

 rapidity of their flight is only sur])assed by its j)erseveranee, while the shortness of 

 their feet ])revent them from moving on the gmund exeejit in the most awkwanl man- 

 ner. In regard to their nesting habits, the swallows m.ay be divided in three 

 groujis : (1) Those which build their nests in hollows of any description, not dug out 

 or prepared by the birds themselves ; to this group belong different species of the 



