I give up! 24d clue: retinal inspection instruments. [I ought to know this having worn specs for nearly 70 years!]
o-h-h-lmoscopes
The first 'h' is in 'ichor' 30a; the second in 'behaviour' 35a. Are they right?
It should be 'opthalmoscopes' but it doesn't fit.
Anyone know of it being spelt opHthalmoscopes?