212 THE NATATOEES. 



sea-birds sleep in these islets night after night, and that each 

 of them will yield half a pound of guano daily. Our lands receive 

 valuable assistance to fertility from this unrivalled material, which 

 owes its power to the ammoniacal salts, phosphate of lime, and 

 fragments of feathers of which it is composed. 



The order of Natatores, or Palmipedes, consists of four families : 

 — 1. Brevipennes, or Divers; 2. Longipennes, or Skimmers; 

 3. Totipalmates, or PeUcanidce ; 4. Lamellirostres, including 

 Geese, Ducks, Swans, and Flamingos. 



The Divers {Brevipennes). 



Penguins, Aptenodytes ; Auks, A lea; Grebes and Divers, 

 Cohjmhus ; Guillemots, Uria. 



The birds which constitute this family of the Natatores are 

 characterised by wings so thin and short as to be totally useless 

 for the purposes of aerial locomotion. They are also called 

 Brachjpteres, from the Greek compound ySpax^?, short, and Trrefja, 

 winged. These are all habitual divers and indefatigable swim- 

 mers, vising their wings as fish do their fins. To raise these 

 after making the down-stroke requires a considerably greater 

 efibrt than a bird of flight makes in raising its wings in the 

 air, for which reason the second pectoral muscle in this and 

 other diving birds has an unusually large development to give 

 further strength. Their plumage is smooth and silky, and im- 

 pervious to water from its oily nature. They live chiefly on the 

 sea, coming ashore in the breeding season. 



The Divers, Colymhus^ are distinguished from other Brachypteres 

 by their beak being longer than the head, straight, robust, and 

 nearly cylindrical, slightly compressed on the sides, acute, the 

 upper mandible longer than the lower ; their toes, in place of being 

 each furnished with marginal membranes, have the three united 

 by a single membrane ; their feet being placed far backward and 

 on the same perpendicular line with the tibia — an arrangement 

 very unfavourable for walking, compelling the birds to take a 

 vertical position, rendering their movements on land both painful 

 and. diflicult. 



They are, however, intrepid swimmers, and they dive with such 



