THE EAR AND HEARING. 
121 
ligament, consisting of a tliin-walled tube, continuous 
with the sheath of the nerve, and filled with a homogeneous 
and slightly granular mass. From an examination of upwards 
of sixty genera he gives as the most usual seat of the organ, 
the hind rudimentary wings (lialteres) amongst the Diptera, 
next the fore wings, and, in the lower orders, the legs. He 
considers that in the Gryllidie (grasshoppers) the tympanum 
and auditory meatus are both represented—the latter by the 
tracheal tubes, and the former by a peculiar enlargement of 
the trachea—whilst he identifies the above noted scolopophorous 
and other chordotonal nerve-endings with the organ of Corti 
(of which we shall treat shortly), and holds that the percep¬ 
tion of auditory sensations is shared with the brain and head, 
by part of the ventral ganglia. 
In the class Antchnida, exemplified by mites, spiders, and 
scorpions, F. Dahl considers that he has established, by 
experiment, the existence of a sense of hearing, which he 
localises in two kinds of hairs found on the legs and palps of 
these arthropods— (a) a hair of equal thickness throughout, 
fringed with a short pile near the apex, implanted in a 
cup-like depression, extremely mobile, and connected with a 
nerve at its base ; and ( b ) a hair set in rows, and projecting 
outwards more than the ordinary protective hairs. 
Some of the hairs on the claw-joints of scorpions are said 
by Dahl to have a like function ; and the pits found by Haller 
in ticks (Ixodes) may possibly come under the same category. 
Amongst the Crustaceans (cyclops, shrimps, lobsters, &c.), 
the ear consists of a small cavity excavated in the solid 
framework of the head. It may be easily found in the 
lobster or crayfish by examining the bases of the smaller 
antenme (antennulge). It is a little prominence of very hard 
shell, having a circular opening at the apex, across which is 
placed a thin membrane. Inside this is a sac filled with liquid, 
having the auditory nerve distributed over its inner surface, 
and containing one or more small bodies called otoliths. 
Siebold was the first to notice the organs of hearing in 
the next sub-kingdon of invertebrates—the Mollusca. In the 
Lamellibranchiates (including mussels, oysters, cockles. &c.), 
they are situated in the foot, and consist of a large central 
ganglion, on each side of which is a minute cavity filled with 
the usual endolympli, and enclosing a small otolith. This 
otolith may be conveniently seen oscillating rapidly in the 
foot of the Cyclas, by using a lialf-incli objective. 
In the Gastropods (snail, whelk, &c.), the ear is at the 
base of the tentacles. It consists of an auditory sac con¬ 
taining otoliths, which vary with the species. 
