8o THE STORY OF THE BIRDS 



their three eggs are very oval in form and 

 spotted with surface and shell markings. The 

 young are hatched covered with down. Sixteen 

 species of Sand-Grouse are at present known to 

 science. 



From the Sand-Grouse we may conveniently 

 pass to the Columbiformes or Pigeons, a re- 

 markably homogeneous and well-defined group, 

 composed of nearly 500 species (470 are re- 

 cognised in the British Museum Catalogue). 

 These birds are allied apparently to the Game 

 Birds, through the preceding order, and to the 

 Plovers. Some authorities divide this order into 

 two sub-orders, but as one of these (Didi) is 

 exclusively composed of extinct forms (the Dodo 

 and the Solitaire), we need not stay to consider 

 them. All living members of this order, ac- 

 cording to Count Salvadori, their most recent 

 monographer, are divisible into five families 

 (some of which are again made up of several 

 sub -families). These are the Treronidae or 

 Fruit Pigeons, Columbidae or Typical Pigeons, 

 Peristeridae or Ground Pigeons and Doves, the 

 Gouridae or Crowned Pigeons, and the Didun- 

 culidae or Tooth-billed Pigeons, of w^hich but 

 one species is known, and that is threatened 

 with extermination. Pigeons vary considerably 



