Hello!!!

Hope you are doing great!!!

The follicles are the one which encloses oocyte .A primary follicle is an immatured ovarian follicle surrounded by single layer of cuboidal cells.They are known as granulosa cells.Secondary follicles consists of many layers of cuboidal cells known as membrana granulosa cells.It secreates follicular fluid.A thick amorphous layer called zonapellucida appears betweem  primary oocyte and membrana granulosa.

Hope it helps!!!!