sound vibrations. The organ of Siebold in the
grasshopper's ear begins with vesicles, of which a few of the first are
nearly equal in size; these vesicles then regularly diminish in size to
the end of the series. Each of these vesicles contains an auditory rod,
and is in communication with the auditory nerve through a delicate
nerve-fibril. I have observed that each of these nerve-fibrils swells into
a minute ganglion immediately after leaving its particular vesicle; the
function of these ganglia is, I take it, to strengthen and reenforce
nerve-energy. No other observer mentions these ganglia, as far as I have
been able to determine; they may have been absent, however, in the
specimens studied by others, yet in the specimens studied by myself--the
"red-legged locust" (_Melanoplus femur-rubrum_, Comstock)[18] and the
"meadow grasshopper" (_Xiphidium_), they were always present.

[18] Consult Comstock, _Manual for the Study of Insects_, p. 110.

That grasshoppers, locusts, and crickets can hear, no one who has
observed these creatures during the mating season will for one instant
deny; they hear readily and well, for in most of them the sense of
hearing is remarkably acute.

Immediately behind the wings of flies two curious knobbed organs are to
be observed; these are considered to be rudimentary hinder wings by
entomologists, and are called the halteres. Bolles Lee and others of
the French scientists call them _balanciers_. This latter name I
consider the correct one, for these organs unquestionably preside over
alate equilibrium: they are true balancers. I do not propose to enter
into any discussion as to whether these organs are rudimentary wings or
not; suffice it to say that they appear to me to be organs fully
developed and amply sufficient to serve the purposes for which they were
created. Whether or not in the process of evolution there has occurred a
change of function, is a point which will not be discussed in this
paper. As they now exist, I deem them to be auditory organs of Diptera
(flies, gnats, etc.).

The semicircular canals are, to a great extent if not entirely, the seat
of equilibration in man. Any derangement or disease of these canals
interferes with equilibration; this is well shown in Meniere's disease,
in which there is always marked disturbance of the equilibrating
function.

If the balancers of a horsefly be removed, the insect at once loses its
equilibrium; it cannot direct its flight, b