16 INTRODUCTION. 



truly piscivorous birds, as the Loons, Auks, and Cormorants, 

 are also placed by themselves, and the series is completed by 

 the Gulls, Terns, Fulmars, and other wandering sea-birds, 

 which feed on fishes chiefly, but also on Crustacea, insects, 

 mollusca, and even birds and mammalia. 



Between the Terrestrial and Aquatic Birds is placed an 

 extended series, of which some species are closely allied to 

 the one. and some to the other, of these groups. Among 

 these " Grallatores" or " Waders," as they are named by 

 authors, there are, in fact, some which are not at all addict- 

 ed to wading, and others which are almost or entirely as 

 much addicted to swimming as the web-footed birds them- 

 selves ; so that, had they not, in their aspect and organiza- 

 tion, a certain evident connexion, the group might be bro- 

 ken up, and its members allotted to the two groups of Land- 

 Birds and Water-Birds. In truth, the question is not much 

 different from that so much agitated among the geologists, 

 whether it be expedient to keep up a Transition class, be- 

 tween the Primary and Secondary series, or to separate the 

 rocks of that class, referring some to the former, and others 

 to the latter. The truth is, there is no real break, no line 

 of demarcation between the Land-Birds and the Waders, or 

 between the latter and the Swimmers. 



Birds have, however, by many authors, been primarily ar- 

 ranged into two series : Terrestrial and Aquatic. The former 

 may be subdivided into two groups : Volatorial, or those 

 which obtain their prey by flying, and Gradatorial, or such 

 as procure it while walking. The aquatic series may, in like 

 manner, be divided into two groups : Grallatorial, or long- 

 legged birds, addicted to wading, and Natatorial, or birds 

 that habitually swim. But, as among the Volatorial birds 

 there may be some that walk occasionally, and among the 

 Gradatorial some that are aquatic, although their affinities 

 shew that they cannot with propriety be elsewhere placed, 

 so among the Waders there are many that seldom, and some 

 that never, enter the water, and among the Natatorial some 



