7 6 



ENTOMOLOGY 



FIG. 90. 



Hairs, Setae and Spines. These occur universally, serv- 

 ing a great variety of purposes; they 

 are not always simple in form, but are 

 often toothed, branched or otherwise 

 modified (Fig. 89). Hairs and bris- 

 tles are frequently tactile in function, 

 over the general integument or else 

 locally ; or olfactory, as on the antennae 

 of moths; or occasionally auditory, as 

 on the antennae of the male mosquito; 

 these and other sensory modifications 

 are described beyond. The hairy 

 clothing of some hibernating cater- 

 pillars (as Isia Isabella) probably pro- 

 Section of antenna of a r 



moth, satumia, to show tects them from sudden changes of 

 developing hairs, c, cutic- temperature. Hairs and spines fre- 



ula; f, formative cell of 



hair; h, hypodermis; t, queiitly protect an insect from its ene- 



trachea. After SEMPER. >> -, . 



mies, especially when these structures 

 are glandular and emit a 

 malodorous, nauseous or 

 irritant fluid. Glandular 

 hairs on the pulvilli of 

 many flies, beetles, etc., 

 enable these insects to walk 

 on slippery surfaces. The 

 twisted or branched hairs 

 of bees serve to gather 

 and hold pollen grains; in 

 short, these simple struc- 

 tures exhibit a surprising 

 variety of adaptive modifica- 

 tions, many of which will be 

 described in connection with 

 other subjects. 



A hair arises from a 

 modified hypodermis cell (Fig. 90), the contents of which 



FIG. 91. 



Radial section through the base of a 



hair of a caterpillar, Pieris rapes, c, cutic- 



ula; f, formative cell; h, hair; hy, hypo- 

 dermis. 



