12 
GENERALIA 
delicate insects; on the other hand the bill of the haw-finch 
is so powerful that it breaks the hardest cherrystone with 
the greatest ease; the tip of the woodcock's bill is a borer, 
which forms in reality an apparatus of touch, and when 
the bird bores into the ground the apparatus like a 
man's finger, enables it to trace the food buried in the 
ground; whereas the beaks of birds of prey are constructed 
for tearing flesh or dividing and are consequently, hooked 
and hatchet- like. And the beak, just as the wing, creates a 
system of work corresponding to the phenomena of nature 
a system which, while providing against the extinction of 
the species, by its influence helps to form extant conditions 
or, in other words, takes its share of the great economy of 
Nature. 
And so it is with the feei of birds too. These too, by 
their own organic differences, form a manifold collection of 
tools, which, beginning from the foot of the threetoed ringed 
plover, present the greatest variety of modifications. In this 
varied collection we find the kingfisher's foot, suitable only 
for perching; that of the woodpecker which is yoke-toed 
(zygodactylic), presenting two toes to the front and two 
to the rear, a formation that enables the woodpecker to 
climb perpendicular or inclined , trees; that of the nu- 
thatch which enables the bird to climb up perpendicular 
or inclined trees and the branches of the same, even in 
an inverted position; that of the swift, the most perfect 
example of the „crab foot", which is only suitable for enabling 
the bird to remain in perfect security upon perpendicular 
surfaces, the claws being as sharp as needles; final those of 
birds of prey, the claws of which are, generally speaking, 
murderous instruments, the sole suitable for throttling, while 
one of the toes (e. g. in the case of the owl) may be moved 
backwards or forwards as required. 
