**Question:** All of the following are coverings of a mature graffian follicle, except:

A. Membrane
B. Zona granulosa
C. Zona radiata
D. Corpus luteum

**Core Concept:**
A mature Graffian follicle is a structure within the ovary, which develops during the menstrual cycle. It consists of several layers of cells surrounding the developing ovum. The correct coverings of a mature Graffian follicle include the Membrane, Zona granulosa, and Zona radiata.

**Why the Correct Answer is Right:**
The correct answer is **D. Corpus luteum**. The corpus luteum is not a covering of the mature Graffian follicle, but rather a result of follicle rupture. It forms after ovulation and secretes progesterone and estrogen, which contribute to maintaining the endometrial lining and preparing the uterus for potential implantation.

**Why Each Wrong Option is Incorrect:**
A. Membrane: Although the membrane surrounds the ovum, it is not a part of the mature Graffian follicle itself but rather a surrounding structure.
B. Zona granulosa: This is a part of the mature Graffian follicle, consisting of granulosa cells that produce sex steroid hormones (estrogen and progesterone) during follicle development.
C. Zona radiata: This is another part of the mature Graffian follicle, consisting of luteinized granulosa cells that produce progesterone upon follicle rupture.

**Clinical Pearl:**
Understanding the anatomy and function of Graffian follicle coverings is crucial for understanding reproductive processes, particularly in relation to the menstrual cycle and potential pregnancy. A thorough knowledge of these structures and their roles helps in diagnosing and treating reproductive disorders.