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. S. 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- 
tenn, palpi and cerci are especially sensitive to tactile impres- 
sions. 
The end-organs of touch are bristles (sensilla chzetica) or 
hairs (sensilla trichodea), each arising from a special hypo- 
dermis cell and having connection with a nerve.  Sensilla 
chetica 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 antennz 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 
