358 Prof. A. M. Mayer’s Experiments on the supposed 
fibril, and hence the direction of the pulses in the wave are in 
the direction of the fibril’s length, the latter cannot be set in 
vibration ; but if the vibrations in the wave are brought more 
and more to bear athwart the fibril, it will vibrate with am- 
plitudes increasing until it reaches its maximum swing of co- 
vibration, when the wave-front is parallel to its length, and there- 
fore the direction of the impulses on the wave are at right angles 
to the fibril. These curious surmises I have confirmed by many 
experiments made in the following manner. <A fork which 
causes a strong covibration in a certain fibril is brought near 
the microscope, so that the axis of the resonant box is perpendi- 
cular to the fibril, and its opening is toward the microscope. 
The fibril in these circumstances enters into vigorous vibration 
on sounding the fork; but on moving the box round the 
stage of the microscope so that the axis of the box always 
points toward the fibril, the amplitudes of vibration of the fibril 
gradually diminish; and when the axis of the box coincides 
with the length of the fibril, and therefore the sonorous pulses 
act on the fibril in the direction of its length, the fibril is abso- 
lutely stationary, and even remains so when the fork in this 
position is brought quite close to the microscope. These ob- 
servations at once revealed to me another function of these 
organs: forif, for the moment, we assume that the antenne are 
really the organs which receive aérial vibrations and transmit 
them to an auditory capsule, or rudimentary labyrinth, then 
these insects must have the faculty of the perception of the 
direction of sound more highly developed than in any other class 
of animals. The following experiments will show the force of 
this statement, and at the same time illustrate the manner in 
which these insects determine the direction of a sonorous centre. 
I placed under the microscope a live mosquito, and kept my at- 
tention fixed upon a fibril which covibrated to the sound of a 
tuning-fork which an assistant placed in unknown positions 
around the microscope. I then rotated the stage of the instru- 
ment until the fibril ceased to vibrate, and then drew a line on 
a piece of paper under the microscope in the direction of the 
fibril. On extending this line I found that it always cut within 
5° of the position of the source of the sound. The antennz of 
the male mosquito have a range of motion in a horizontal di- 
rection, so that the angle included between them can vary con- 
siderably inside and outside of 40°* ; and I conceive that this is 
the manner in which these insects during night direct their 
flight toward the female. The song of the female vibrates the 
* The shafts of the antenne include an angle of about 40°. The basal 
fibrils of the antenne form an angle of about 90°, and the terminal fibrils 
an angle of about 30°, with the axis of the insect. 
