74 



THE BIOLOGY OF INSECTS 



(Fig. 25) shows that the normal thick cuticle is interrupted, 

 and that just in or beneath the aperture is a long, narrow- 

 ended spindle-shaped cell or a group (s) of such cells ; often 

 delicate processes (p) from the cells project towards the 



pore, and these may 

 possibly be exposed 

 to the outer atmo- 

 sphere, though they 

 do not protrude 

 through the pore so 

 as to be liable to 

 contact with external 

 solid objects. Such 

 nerve-endings are not 

 tactile, but they are 

 adapted to receive 

 chemical stimulation 

 by vapour diffused 

 through the air from 

 some odoriferous 

 substance in food- 

 material or in the 

 body of another in- 

 sect, or from minute 

 floating particles. In 

 many, if not all, of 

 these sensory pits, 

 however, the nerve- 

 endings are covered 

 by extremely thin 

 and delicate cuticle, 

 through which odori- 

 ferous or tasty sub- 

 stances might readily be absorbed if dissolved in the fluid 

 secreted by the glandular cells said to be often associated 

 with these organs (A. Berlese, 1909). Nerve-endings of 

 closely similar form and arrangement to those of the 

 sensoiy pits of insects are well known in vertebrate animals 



Fig. 25.— Section through Feeler of Syrphid 

 Fly ( Volucella bombylans) , showing cuticle {c) 

 with pore {a) leading to sense-organ con- 

 sisting of processes {p) arising from sensory 

 cells {s) of the skin or epidermis {e). n, nerve 

 to brain. X 600. After K. M. Smith 

 {Proc. Zool. Soc. 1 919). 



