INTRODUCTION- 
viii 
of the fecond clafs — the fivlmmers. Some of thefe, likewifc, 
after having reared their young, migrate much in the fame 
way as the waders. 
The ornithologift, who does not content himfelf with bare 
names and appearance, in examining the economy of the vari- 
ous kinds of birds, and the ftrufture of their feveral parts, will 
find ample room for the exercife of his labours in the moft mi- 
nute inveftigation ; and although he can fcarcely overlook the 
flow, and almoft imperceptible degrees, by which nature has re- 
moved one clafs of beings from another, yet in his attempts to 
trace the relationfliip, or affinity, which one bears to another, he 
will, with his utmoft care, find himfelf at a lofs to afcertain that 
precife link in the chain, where the doubtful croffing line is 
drawn, and by which the various genera and fpecics are to be 
feparated. But, however, after he (hall have examined a few 
gradations, upwards or downwards, he will more readily difco- 
ver the modes of life which the feveral kinds are deftined to 
purfue ; and their ability to perform the various evolutions ne- 
ceffary for the procuring of their food in that exadtitude to 
which the Author of nature hath formed them. In fome of 
thofe which run on the furface of the foft mud, and can occa- 
fionally take the water, the indications of their ability for fwim- 
ming are furniflied very fparingly : thefe indications firfl; appear 
in the breadth of the underfides of the toes, with the two outer 
toes joined by a fmall web. The fcalloped membranes attached 
to the fides of the toes form the next advance : fome are webbed 
to the nails, with deep indentations in the middle, between each 
toe ; others have only three toes, all placed forwards, and fully 
united by webbed membranes : fome have the addition of back 
toes, either plain, or with webbed appendages to each 5 and 
others again have the four toes fully webbed together. The 
thighs, In the moll expert divers, are placed very far back ; their 
legs are almoll as flat and thin as a knife ; and they are enabled 
to fold up their toes fo clofely, that the lead poffible refiftance is 
