636 



CLASS IV. INSECTA. 



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- 

 cidae are set in vibration by the humming of 

 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 Acri- 

 diidae a more specialized organ is found on 

 the anterior segment of the abdomen. This 

 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, 



GryUidae 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- 



FIG 395. Longitudinal section of por- 



bably Organs of taste, whilst Others tion of caudal appendage of Acheta 



domestica (after Vom Bath). ch 



on the palps may subserve the tune- 



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. 



FlQ. 394. 'Tibia 

 of the anterior 

 leg of Locusta 

 viridissima (after 

 V. Graber). Ty 

 tympanic mem- 

 brane with oper- 

 culum 



hyp hypodermis ; n nerve ; 

 /i 1 integumental hairs, not sensi- 

 tive ; h- ordinary hair ; h 3 sensory 

 hair ; h bladder-like hair ; sz 

 sense-cell. 



