38 NERVOUS SYSTEM AND SENSE-ORGANS 
their fellows, a well-known instance being afforded by Grass- 
hoppers and Crickets. A Grasshopper possesses a chirping 
arrangement something like that of the 
Musical Strand-Crab (p. 37). The wing- 
cover is provided with a sharp edge or 
scraper which is rubbed along a key-board 
placed on the inner edge of the thigh of 
the hind-leg (fig. 1048). The chirping 
sounds audible to our own ears are pro- 
duced by the male insect, but the females of 
some species are also provided with these 
“stridulating” organs, which nd doubt 
make sounds that can be heard and ap- 
preciated by the opposite sex. These 
o-4 324 sound-producing insects also posses’ what 
eee we may feel justified in calling ‘ears ”. 
eee pe munopes: (Stents), On either side of the first ring of the 
showing beaded key-board (dotted line 7 
onright), enlarged; B,fivebeadsofsame, abdomen there is a membrane compar- 
snr bea kya of ele able to a drum-head (fig. 1048) stretched 
hopper (Acridium), to show ear; wings OVEr an air-space, and closely connected 
rata eae atdominal cigaa ® with sensory arrangements somewhat like 
those already described for a gnat-larva. 
The ears of Green Grasshoppers and Crickets are situated in the 
shins of the fore-legs, just below the knee. 
OrGANS OF BaLaNcE AND HeEarinc IN BackBoNED ANIMALS 
(VERTEBRATA).— The tadpole 
larve of Sea- Squirts pos- 
sess remarkable sense-organs 
formed by specialization of 
part of the wall of the brain, 
and projecting into its cavity. 
One of these is of the nature 
of an otocyst, and is pro- 
Pere: bably a balanci fi 
Fig. 1049.—Body of an Ascidian Tadpole, in longitudinal y a ba ancing organ ( g- 
section, enlarged. The tail is cut short; the dorsal nerve-tube IO. ) 
(z.2.) swells into a brain, into which project a balancing organ 49). 
(6.) and an eye (¢.); @., atrial cavity; c., groups of embryonic From Fishes onwards we 
cells; g., gut; #., mouth; ., notochord; /., adhesive papilla. 
find undoubted ears, similar, 
broadly speaking, to the essential parts of our own organs of 
hearing, and there can be no doubt that these also have to do with 
equilibrium and movement. If we trace the development of the 
