THE PRINCIPAL BIRD GROUPS 67 



Birds the central feathers in the tail are much 

 prolonged ; in the Cormorants and Gannets it 

 is wedge-shaped ; in the Frigate Birds it is 

 acutely forked ; in the Darters it is broad and 

 fan-shaped. The wing bones of the last are 

 very specially modified, the furcula coalescing 

 with the coracoids, whilst the latter similarly 

 join with the proximal end of the scapula, result- 

 ing in a nearly rigid framework. This peculiarity 

 is believed to be closely connected with the 

 extraordinary soaring or sailing flight of these 

 birds. The neck of the Darters also presents us 

 with a feature believed to be unique amongst 

 birds, the eighth vertebra articulating with the 

 seventh nearly at a right angle, causing a " kink," 

 whilst the muscles connected with this are also 

 specially modified, the whole forming a beautiful 

 apparatus by which the birds secure, with the 

 least possible exertion, the fish upon which they 

 subsist. We also find great diversity of plumage 

 in this order, from the pure white of the Gannet 

 or the Pelican (in the latter with a rosy blush) 

 to the bottle-green of the Cormorant, or the 

 loricated blackish-brown of the Frigate Bird. 

 In many species elaborate nuptial filoplumes 

 and other ornaments are assumed. In most 

 species the young are hatched naked, but soon 



