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 no doubt 

 make sounds that can be heard and ap- 

 preciated by the opposite sex. These 

 sound-producing insects also possess what 



10-4 



Fig. 1048. Stridulating Organs and r -i r 11 



we may feel justified in calling 



ears 



Ears of Grasshoppers. A, Hind-thigh 

 of a male Grasshopper (Stenobothrus), 

 showing beaded key-board (dotted line 



onright),eniarged;B,nvebeadsofsame, abdomen there is a membrane compar- 



further enlarged; c, six of the much x 



smaller beads of key-board of a female 



(same scale as B) ; D, side view of a Grass- . ill i 



hopper (Acridium], to show ear; wings over an air-space, and closely connected 



n.t. 



On either side of the first ring of the 

 abdomen there is a membrane compar- 

 able to a drum-head (fig. 1048) stretched 



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 HEARING IN BACKBONED ANIMALS 



(VERTEBRATA). The tadpole 

 larvae 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- 

 bably a balancing organ (fig. 

 1049). 



From Fishes onwards we 

 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 



c. g. 



Fig. 1049. Body of an Ascidian Tadpole, in longitudinal 

 section, enlarged. The tail is cut short; the dorsal nerve-tube 

 (n.t.) swells into a brain, into which project a balancing organ 

 (.) and an eye (#.); -, atrial cavity; c., groups of embryonic 

 cells; g., gut; m., mouth; n., notochord; /., adhesive papillae. 



