BALANCE AND HEARING 37 
of the higher Crustaceans are able to emit sounds, it is quite 
possible that their otocysts are beginning to acquire a new 
use, ze. that of serving as auditory organs. The Rock-Lobster 
(Palinurus), for example, makes a creaking noise by moving 
the basal joints of the large feelers, which then rub against 
their sockets. An unpleasant sound of similar nature can be 
produced by twisting a glass stopper in the neck of its bottle. 
A more specialized case is that of the Musical Strand-Crab 
({Ocypoda macrocera), which has been described by Alcock (in 
A Naturahst in Indian 
Seas). In this animal the 
inner side of the large 
nippers is provided with 
a ridge or scraper placed 
near the base of the limb, 
and a rasp-like ridge or 
key-board on the fixed joint 
of the claw. By drawing 
the scraper over the key- 
board a sort of chirping 
sound is produced, not ks 
. . 2 Fig. 1047.—Chordotonal Organs. On the right is shown part of 
unlike the one with which an abdominal segment of the larva of a Gnat (Corethra plumicor- 
nis), seen as a transparent object, enlarged. In the centre is the 
our native gr asshoppers nerve-cord (darkly shaded) with the ganglion (gz.) of the segment; 
ss é.nz., longitudinal muscles; ch.z., ch.g., ch.d., and ch., chordotonal 
have made us familiar. nerve, ganglion, ligament, and organ; ¢.4., branched tactile bristles. 
The same zoologist speaks 9p ete st ara he canal wenn wi oth 
of the Squeaker Crab 
(Psopheticus stridulans) of the Andaman Sea as making a dismal 
noise by rubbing a spine which projects from the base of its 
nippers against a rough knob near the eye-socket. 
Orcans oF BALANCE AND HearinG In Insects (INsECTA).— 
A variety of organs situated in different parts of the body are 
probably connected with balance or hearing, or both. Among 
those which are most likely concerned with equilibrium and move- 
ment are certain peculiar structures (chordotonal organs) that 
are especially characteristic of aquatic larve, though not limited 
to these. Gnat larve, for example, possess such organs, one of 
which is represented in fig. 1047. It consists essentially of a 
group of rod-shaped cells contained in a tube that opens to 
the exterior. 
Many insects make sounds which are doubtless heard by 
