26 The Structure and Special Physiology of Insects 
Insects certainly have the senses of touch, hearing, taste, smell, and sight. 
If they have others, we do not know it, and probably cannot, as we have 
no criteria for recognizing others. 
The tactile sense resides especially 
in so-called “ tactile hairs,” scattered 
more or less abundantly or regu¬ 
larly over the body. Each of these 
hairs has at its base a ganglionic 
nerve-cell from which a fine nerve 
runs to some body ganglion (Fig. 51). 
They are specially numerous and 
conspicuous on the antennae or 
“ feelers,” and often on certain pro¬ 
cesses called cerci, projecting from 
the tip of the abdomen. They may 
occur, however, on any part of the 
body, and are usually recognizable 
by their length and semi-spinous nature. The sense of taste resides 
in certain small papillae, usually two-segmented, or in certain pits, which 
Fig. 51.—Diagram showing innervation of a 
tactile hair, sh., tactile hair; ch ., chitinized 
cuticle; hyp., hypoderm, or cellular layer 
of the skin; s.c., ganglion cell; c.o., gan¬ 
glion of the central nervous system. (After 
vom Rath.) 
Fig. 52. Fig. 53. 
Fig. 52. —Nerve-endings in tip of maxillary palpus of Locusta viridissima. s.h., sense- 
hairs; s.c., sense-cells; b.c., blood-cells. (After vom Rath; greatly magnified.) 
Fig. 53.—Nerve-endings in tip of labial palpus of Machilis polypoda. (After vom 
Rath; greatly magnified.) 
occur on the upper wall of the mouth (epipharynx) and on the mouth- 
parts, especially the tips of the maxillary and labial palpi, or mouth- 
feelers. As substances to be tasted have to be dissolved, and have to 
