Sentence:  In the simplest form of this system, applicable to many microscopes, the substage polar consists only of semicircles of <WSD>polaroid</WSD> orientated to give respective planes of polarisation at right angles. <WSD>Polaroids</WSD> over the eyepieces are orientated so extinguish the inner halves of the exit pupils. 
Meaning of the word marked with <WSD> tags:  A sheet of plastic embedded with microscopic crystals of herapathite or similarly acting material, so that light passing through it is polarised.