50 
ON THE CTiASSIFIOATION OF BIRDS. 
should be the chief instrument of procuring food ; it is 
therefore large and fleshy. But in birds which gulp 
their food the instant it is captured, the tongue apparently 
is of no sort of use ; U is therefore reduced to a mere 
rudiment : such is the case with the swallows and night- 
jars. There must be something very analogous to the 
same mode of feeding in the genus Casmorhynchus ; for 
on dissecting more than one specimen of C. nudicoUin, we 
found the tongue fully as small, and the mouth as wide, 
as in the ordinary Caprimulgidw. The food of the duck 
is discriminated solely by the tongue, while that of the 
swallow is selected by the eye ; and hence this remarkable 
difference in their respective tongues. Hitherto we have 
noticed those forms only in which the length of this 
member is regulated by that of the bill; but there is 
another structure which is not uncommon, and by which 
the bird is able to protrude it to twice its usual length ; 
hence such tongues are called extensible : of these there 
are two distinct modifications, — one possessed by the 
woodpeckers, the other by the honeysuckers. On opening 
the bill of a woodpecker, immeiliately after it is killed, 
the tongue seems to be of the ordinary length, rather 
short, and shaped vey much like the heads of those 
spears used by the Gaffers of Southern Africa, and called 
assagais, being pointed at the end, with numerous little 
barbs on the sides : this, however, is only the head or 
point of the tongue ; draw it out of the mouth, and a 
person unacquainted with its formation .would fancy he 
had got hold of a very long earth-worm, which the bird 
had Incautiously devoured, and which had stuck in its 
throat. 'I'liis description, unscientific though it be, will give 
the reader a much better idea of the tongue of the wood- 
pecker, than the most elaborate anatomical character we 
could draw up. A tongue so formed, in allusion to the ap- 
pearance it assumes, is called vermiform : the point re- 
poses, in the ordinary manner, between the mandibles of 
the bill; the rest is concealed, and from being elastic is 
capable of lieing thrown out, at the pleasure of the bird, 
to four or five times the length of the bill itself. This 
