122 



SENSES 



CHAP. 



particular function to any of them, except it be to the sensory 



hairs. These are seated on various 

 parts of the body. The chitinous 

 covering, being a dead, hard substance, 

 has no nerves distributed in it, but it 

 is pierced with orifices, and in some of 

 these there is implanted a hair which 

 at its base is in connexion with a 

 nerve ; such a structure may pos- 

 sibly be sensitive not only to contact 

 with solid bodies, but even to vari- 



Fia. 67. -Longitudinal "Action of ^^^ ^inds of vibration. We givc^ a 

 portion of caudal appendage of figure (Fig. 67) of some of these hairs 



Acheta domestica (after Vom i-i^ -ii ^ p -li 



Rath) : ch, chitin ; hyp, hypo- ^^^ ^^^ ^^^^^1 appendage of a cricket, 

 dermis ; n, nerve ; W-, integu- after Yom Eath. The Small hairs on 



mental hairs, not sensitive ; /r, .i , n p , , , ., . . ,, . 



ordinary hair ; /i^, sensory hair ; ^^^ ^^^iCr SUrtace Ot the chltm in thlS 



h*, bladder-like hair ; sz, sense- figure have no sensory function, but 



each of the others probably has ; and 



these latter, being each accompanied by a different structure, 



/>A sck 



must, though so closely approximated, 

 be supposed to have a different function ; 

 but in what way those that have no 

 direct connexion with a nerve may act 

 it is difiicult to guess. 



The antennae of Insects are the seats 

 of a great variety of sense organs, many 

 of which are modifications of the hair, 

 pit and nerve structure we have described 

 above, but others cannot be brought 

 within this category. Amongst these 

 we may mention the pits covered with 

 membrane (figured by various writers), 

 perforations of the chitin without any 

 hair, and membranous bodies either con- 

 cealed in cavities or partially protruding 

 therefrom. 



Various parts of the mouth are also 

 the seats of sense organs of different kinds, some of them of a 

 compound character ; in such cases there may be a considerable 

 number of hairs seated on branches of a common nerve as figured 



Fig. 68. Longitudinal section 

 of apex of palpus of Pieris 

 hrassicae : sch, scales ; ch, 

 chitin ; hi/p, hypodermis ; 

 n, nerve ; sz, sense cells ; 

 sh, sense hairs. (After 

 Vom Rath. ) 



