618 THE SENSES AND SENSORY ORGANS. 
distinct vision (see p. 570). They run well, but will not climb 
vertical surfaces; and if placed upon their backs, they recover 
themselves like a beetle, with their legs. 
Conclusions.—I conclude from the above facts that these 
organs are organs of co-ordination, acting through the nervous 
system, and that the organs at the base are probably concerned 
in receiving sensory impulses, which enable the insect to main- 
tain equilibrium; in other words, that they are analogous to 
the semicircular canals of Vertebrates in their functions. 
It was formerly commonly believed that the halteres act 
mechanically, like the pole of a rope-dancer ; hence the term 
‘halteres,’ which signifies a rope-dancer’s pole. Their small 
size is obviously against such an hypothesis. 
Weinland apparently thinks they act by shifting the centre 
of gravity or the centre of equilibrium by their rapid move- 
ments, and speaks of the weight of the capitella. This view is 
certainly untenable from a mechanical point of view. The 
movements of the wings, legs, and abdomen must be a thou- 
sand times more important than those of the halteres, which 
cannot have more than a minimal effect on the moment of 
inertia, or on the centre of gravity of the body of the insect. 
The Halteres considered as Organs of Hearing.—Leydig [269] 
first ascribed the function of hearing to the halteres. I formerly 
suggested [82], in 1870, that their structure is similar to that 
of an auditory organ. Graber [285], whilst he describes chordo- 
tonal organs in the halteres, does not do more than suggest 
that they are concerned in audition. 
The probability of their possessing some power of perceiving 
sound vibrations appears to me to be a problem which rests on 
precisely similar grounds with the auditory function of the 
semicircular canals of Vertebrates. 
Effect of the Vibrations of the Halteres.—It has been objected 
that the vibrations of the halteres render them unfitted to 
receive sound-vibrations, but this objection appears to me to 
be invalid on physico-mathematical grounds; indeed, I am 
inclined to regard their vibration as a circumstance greatly 
enhancing their value as sound-perceiving organs. 
