96 ENTOMOLOGY 



tion doubtful ; not auditory and probably not olfactory, though 

 the function is doubtless a mechanical one; Schenk suggests 

 that they are affected by air pressure, as when a bee or wasp 

 is moving about in a confined space. 



7. 5. ampullaceum a more or less flask-shaped cavity with 

 an axial rod (Figs. 124, 125). Probably auditory. 



These types of sensilla will be referred to in physiological 

 order. 



Touch. The tactile sense is highly developed in insects, 

 and end-organs of touch, unlike those of other senses, are com- 

 monly distributed over the entire integument, though the an- 

 tennae, palpi and cerci are especially sensitive to tactile impres- 

 sions. 



The end-organs of touch are bristles (sensilla chsetica) or 

 hairs (sensilla trichodea), each arising from a special hypo- 

 dermis cell and having connection with a nerve. Sensilla 

 chaetica doubtless receive impressions from foreign bodies, 

 while sensilla trichodea, being best developed in the swiftest 

 flying insects and least so in the sedentary forms, may be 

 affected by the resistance of the air, when the insect or the air 

 itself is in motion. 



Not all the hairs of an insect are sensory, however, for many 

 of them have no nerve connections. 



In blind cave insects the antennae are very long and are ex- 

 quisitely sensitive to tactile impressions. 



Taste. The gustatory sense is unquestionably present in 

 insects, as is shown both by common observation and by pre- 

 cise experimentation. Will fed wasps with sugar and then 

 replaced it with powdered alum, which the wasps unsuspect- 

 ingly tried but soon rejected, cleaning the tongue with the 

 fore feet in a comical manner and manifesting other signs of 

 what we may call disgust. Forel offered ants honey mixed 

 with morphine or strychnine; the ants began to feed but at 

 once rejected the mixture. In its range, however, the gusta- 

 tory sense of insects differs often from that of man. Thus 

 Will found that Hymenoptera refused honey with which a 



