"The humming of the screws overhead dropped an octave and a half, back through wasp and hornet to bumble-bee, to cockchafer, to stag-beetle."
Stag Beetle
Creative Commons Attribution Share AlikeStag Beetle - Credit: B kimmel/Wikimedia Commons

Huxley is describing the sound of a helicopter decelerating. Huxley demonstrates his profound talent through this use of metaphor.

 

       
Bumble-Bee
Creative Commons Attribution Share AlikeBumble-Bee - Credit: Trounce/Wikimedia Commons
 
Cockchafer
GNU Free Documentation LicenseCockchafer - Credit: Rasbak/Wikimedia Commons