76 



ENTOMOLOGY 



Section of antenna of a 

 moth, Saturnia, to show 

 developing hairs, c, cutic- 

 ula; f, formative cell of 

 hair; h, hypodermis; t\ 

 trachea. After SEMPER. 



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

 FlG ing a great variety of purposes ; they 



^ , are not always simple in form, but are 



f I/ g|g ^^ often toothed, branched or otherwise 

 J^^&Jlllr 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- 

 tects them from sudden changes of 

 temperature. Hairs and spines fre- 

 quently protect an insect from its ene- 

 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 rapce. c, cutic- 



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

 dermis. 



