636 



CLASS IV. INSECTA. 



FIG. 



of 

 leg 



hairs scattered over the body, and in some of the Diptera the 

 hairs on the antennae, are sensitive to sound. Such hairs are 

 termed chordotonal organs. The numerous, 

 delicate hairs on the antennae of the male Culi- 

 ^Tv pff^^H cidae are set in vibration by the humming of 

 \ : -'^'ml// the female and their heads are readily turned 

 in the direction of the female when she begins 

 to buzz. The basal joint of the antennae forms 

 a socket richly supplied with sense organs and 

 containing a large ganglion. The inclination of 

 the antennae lodged in this socket doubtless con- 

 veys much information to the gnat. In the Aeri- 

 diidae a more specialized organ is found on 

 the anterior segment of the abdomen. Thi& 

 is provided with a drum or tympanum sur- 

 rounded by a chitinous ring. On the inner 

 face of the tympanum are a couple of horn-like 

 processes to which a vesicle full of fluid is 

 attached. This vesicle is said to act like the 

 membranous labyrinth ; it is in connexion with 

 the auditory nerve which arises from the third 

 thoracic ganglion. Somewhat similar 

 structures are found on the tibiae of 

 the anterior legs of the Locustidae, 

 Gryllidae and Termitidae (Fig. 394). 

 (iv) Organs of taste and touch. In- 

 sects undoubtedly have marked 

 preferences, but it is difficult for 

 us to distinguish between their 

 organs of taste, smell and touch. 

 Certain hairs on the epipharynx and 

 other parts of the mouth are pro- 

 bably organs of taste, whilst others 

 on the palps may subserve the func- 

 tions both of taste and touch. The 

 body of an Insect being encased in 

 a hard unyielding exoskeleton is 



mainly dependent on certain hairs (well supplied with nerves; 

 (Fig. 395) which project from almost all parts of the body) for 

 the knowledge it gains of the outer world by touch. 



391. 'Tibia 

 the anterior 

 of Locusta 

 viridissima (after 

 V. Graber). Ty 

 tympanic mem- 

 brane with oper- 

 culum 



FIG 395. Longitudinal section of por- 

 tion of caudal appendage of Acheta 

 domestica (after Vom Hath), ch 

 chitin ; hyp hypodermis ; n nerve ~ 

 fti integumental hairs, not sensi- 

 tive ; h 2 ordinary hair ; /z 3 sensory 

 hair ; A 4 bladder-like hair ; sz 

 sense-cell. 



