xii INTRODUCTION. 
may be regarded as exhibiting some degree of affinity to the previous order, while at the same 
time they distinctly lead through a succession of forms, such as the Spoonbills, Storks, Herons 
and Gallinules, to the true water birds, to which in their aquatic habits the Gallinules very 
beautifully approximate. 
Our fifth volume contains the birds of the Natatorial Order, or swimming birds, which are 
represented by the Ducks, Grebes, Divers, Auks, Pelicans and Gulls; the aerial representative 
of one of these latter groups, viz. the Tachypetes, or Frigate Bird, among the Pelicans, exhibits 
several traits of resemblance to the Raptores, or birds of prey. 
