l64 ON THE CLASSIFICATION OF BIRDS. 
fact is establisheol by experience, and by comparative 
anatomy : we know that the crowing of a cock may be I 
heard at a far greater distance than the shout of a man, I 
even had he the lungs of Stentor, and it may be even 
questioned whether the same remark may not be appli- 
cable to the full and sonorious warbling of the thrush. 
We have no data to estimate the comparative loudness 
of voice between quadrupeds and birds, in proportion to 
their sizes : nor is it very material to labour upon such 
nice distinctions. It is only in these two typical classes 
of the vertebrated circle, if we except the hissing of ser- 
pents, and the croaking of frogs, that the voice is suf- 
ficiently developed to emit sounds, audible and definite. 
The voice of many quadrupeds is capable of different > 
degrees of intonation which, as they arc understood by 
their kind, is without doubt a language. The lowing 
of the cow, when slowly wending “o’er the lea,” to the 
farm yard, is very different from that which it utters 
when separated from its young ; and, again, from the ' 
bellowings of fear or of rage. In the dog, how many 
varied intonations will be found: but it is among 
birds alone that these sounds assume harmonious grada- 
tions. But has nature restricted the power of uttering 
sounds to the vertebrated circle ? Kvery entomologist 
knows the contrary. A large portion of the natural order 
of Hemipteru Lin., among insects, are, perhaps, the most 
noisy beings in creation ; nor is this noise altogether 
unmusical : the ancients, indeed, so much admired the 
shrill chirpings of the Cicada, that one of their poets i 
has made this insect the subject of an ode. Now the 
order Ilemiptern , in the circle of the class Ptiloln, or 
winged insects, occupies precisely the same station as the 
class of bii'ds tills in the circle of the vertebrata. So 
that nature, ever true to her beautiful system of repre- 
sentation, makes the Hemiptera, by this peculiar faculty, 
to be the birds of the insect world : both perch upon trees 
and both sing (though by different means), for a long 
continuance, and in their most alluring notes, during the 
season of courtship. Detach the Cicadas from the 
