CXVi 
and Homoptera, and to them, even more than to the vibrations of the 
wings, the characteristic sounds produced by so many of these insects 
are ascribable. The “song” of the Cicada, for instance, is thus pro- 
duced by the metathoracic ganglia, but without the assistance of 
figures it would be difficult to give any idea of the machinery which 
is described in detail by Dr. Landois, and of which I will here only 
observe that it differs considerably in different insects. 
In the Diptera and Libellulina it is by the four thoracic spiracles 
that the sounds are produced, while in Hymenoptera, as for 
instance in Bombus, the abdominal spiracles are also musical. ‘The 
sounds produced by the wings are constant in each species, excepting 
where there are (as in Bombus) individuals of very, different sizes. In 
these the larger specimens give generally a higher note. Thus the 
male of Bombus terrestris hums in 4’, while the large female is a 
whole octave higher. There are, however, small species which give 
a deeper note than larger ones, on account of the wing-vibrations not 
being of the same number in a given time. 
Moreover, a tired insect produces a somewhat different note from 
one that is fresh, on account of the vibrations being slower. 
Indeed, from the note produced we can calculate the rapidity of 
the vibration. Thus the house-fly, which produces the sound of F, 
vibrates its wings 21,120 times in a minute, and the bee, which makes 
the sound of a’, as many as 26,400 times, or 440 times in a second. 
On the contrary a tired bee hums on zk’, and therefore vibrates its 
wings only 330 times in a second. . 
This difference is probably involuntary, but the change of “ tone ” 
is evidently under the command of the will, and thus offers another 
point of similarity to a true “voice.” A bee in the pursuit of honey 
hums continually and contentedly on a’, but if it is excited or 
angry it produces a very different note. Thus, then, the sounds of 
insects do not merely serve to bring the sexes together; they are not 
merely “love-songs,” but also serve, like any true language, to 
express the feelings. 
Dr. Landois describes the muscles by means of which the form of 
the organ is altered, and the tone is, no doubt voluntarily, affected. 
We can indeed only in few cases distinguish the differences thus pro- 
duced ; but as even we, far removed as we are in organization, habits 
and sentiments, from a fly or a bee, can yet feel the difference between 
a contented hum and an angry buzz, it is highly improbable that their 
power of expressing their feelings should stop here. Oue can scarcely 
