This image shows a Graafian (mature) follicle.  The cavity of the follicle (antrum) is filled with a fluid called the liquor folliculi,  which has a high concentration of estrogens. The follicular cells lining the antrum form a layer called the stratum granulosum.  The cells of the stratum granulosum that surround the developing ovum form a layer called the corona radiata.  The acellular material between the corona radiata and the ovum is the zona pellucida ("clear zone").  Some of these granulosa cells are formed into a golf-tee like structure termed the cumulus oophorus that supports the corona radiata and developing ovum. Outside the stratum granulosum is a two-layered structure called the theca.  The theca interna (next to the stratum granulosum) contains large, glandular cells and is responsible for secreting androgens that will be converted into estrogens by the granulosa cells.  The outer theca externa is comprised of connective tissue fibroblasts and their fibers.