2.6 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 



FIG. 51. Diagram showing innervation of a " feelers," and often on certain pro- 

 tactile hair, sh., tactile hair; ch., chitinized ,, , . . , . , 



cuticle; hyp., hypoderm, or cellular layer cesses called cerci > projecting from 



of the skin; s.c., ganglion cell; c.o., gan- the tip of the abdomen. They may 



vo^Raih) CCntral nerV US SyStCm ' (AftCr OCCUr ' however > on an y P art of th e 



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. 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 



