or members of the insect body; hence their retraction by
insects when alarmed is an instinctively protective action. They shelter
them as much as possible in order to keep them from being injured.
Again, although the antennae of most insects are provided with numerous
sensitive hairs, or setae, we have no right to assume that these hairs
are auditory; no "auditory rods," otoliths, etc., are to be found
generally in antennae, yet there are exceptional instances. Leydig found
auditory rods in the antennae of _Dyticus marginalis_ (Furneaux[17]), the
giant water-beetle, and I myself have observed them in _Corydalis
cornuta_ and other neuropterous insects. I am inclined to believe that
the entire order of Neuroptera has antennal ears, and should therefore
in this respect be classed with Lepidoptera.

[17] Consult Furneaux, _Life in Ponds and Streams_, p. 325.

In grasshoppers and crickets the ears are situated in the anterior pairs
of legs. If the tibia of a grasshopper's anterior leg be examined, two
(one before and one behind) shining, oval, membranous disks, surrounded
by a marginal ridge, will be at once observed. These are the tympana or
ear-drums of the ear of that leg. Where the trachea, or air-tube, enters
the tibia it becomes enlarged and divides into two channels; these two
channels unite again lower down in the shaft of the tibia. The tracheae
of non-stridulating grylli are much smaller than those of
sound-producing grasshoppers. The same may be said of the tibial
air-tubes of the so-called dumb crickets. In grasshoppers and crickets
the ear-drums lie bathed in air on both sides--the open air on the
external side and the air of the air-tube, or trachea, on the inside.
Lubbock calls attention to the fact that "the trachea acts like the
Eustachian tube in our own ear; it maintains an equilibrium of pressure
on each side of the tympanum, and enables it freely to transmit
atmospheric vibrations."

In grasshoppers the auditory nerve, after entering the tibia, divides into
two branches, one forming the supratympanal ganglion, the other descending
to the tympanum and forming a ganglion known as Siebold's organ. This
last-mentioned ganglion is strikingly like the organ of Corti in our own
ear, and undoubtedly serves a like purpose in the phenomenon of audition.
The organ of Corti is composed of some four thousand delicate vesicles,
graduated in size, each one of which vibrates in unison with some
particular number of