Mark the odd term in each series: Give category for the rest of terms.

Leydig cells; corpus luteum; Graafian follicle; Sertoli cells.

Sertoli cells

1. Leydig cells are situated adjacent to seminiferous tubules and secrete the hormone testosterone.
2. The Corpus luteum in the ovary produces oestrogen and progesterone.
3. The graafian follicle of the ovary secretes luteinizing hormone and progesterone.
4. Leydig cells, corpus luteum, and Graafian follicle all are endocrine glands as they produce hormones.
5. Sertoli cells helps in spermatogenesis in the testis.

Hence, Sertoli cells is the odd one out and others belong to endocrine glands and produce hormones.