ut plunges headlong to the
ground. The same can be said of _Chrysops niger_--in fact, of the entire
family of Tabanidae, of the gall gnat (_Diplosis resinicola_, Comstock),
and of the March flies (_Bibionidae_). These widely differing flies
constitute the material from which I have derived my data; I will
venture to assert, however, without fear of contradiction, that what
has been said about the flies mentioned above is equally true of all
flies.

When the knobbed end of the balancers of the horsefly (_Tabanus
atratus_, Comstock)[19] are examined with the microscope, the cuticle
will be found to be set with minute hairs or setae; some of these hairs
penetrate both cuticle and hypoderm, are hollow, and receive into their
hollows delicate nerve-fibrils. These nerve-fibrils pass inward toward
the centre, and enter ganglia, which in turn are in immediate connection
with the great nerves of the balancers. There is but one nerve in the
insect's body that is larger than the balancer nerve, and that is the
optic nerve; hence, it is natural to infer that the balancer nerve leads
to some special sense centre. This centre in my opinion is,
unquestionably, the seat of the auditory function.

[19] Consult Comstock, _loc. cit. ante_, p. 455.

It has been demonstrated beyond doubt that analogous hollow hairs, or
setae, are prominent factors of audition in many animals, notably
crustaceans, such as the lobster, the crab, and the crayfish, and many
of the insect family; hence, it is logically correct to conclude that
the hollow hairs on the balancers of flies are likewise auditory hairs.
Moreover, there are grouped about the bases of these knobbed organs
certain rows of vesicles, which contain auditory rods almost identical
in appearance with the auditory rods of the grasshopper. Indeed, I have
found those in the upper row of vesicles to be precisely similar in
appearance to the rods found in Melanoplus.

I have determined that in the horsefly (_Tabanus atratus_) there are six
rows of these vesicles, and that they are graduated in size. There are
in the knobs of the balancers minute spiracles (I do not think that
these have been pointed out before by any other observer) through which
air passes into the large, vesicular cells which make up the greater
portion of the knobs; spiracles are also to be found in the shafts of
the balancers, thus providing an abundance of air to the internal
structures of these organs and allowing for t