Graafian follicle are characteristically found in the

The correct option is ovary of mammal.

Step-by-Step Explanation:

1. Definition of Graafian Follicle:
A Graafian follicle (also known as a mature ovarian follicle) is a fluid-filled cavity in the ovary that surrounds, protects, and nourishes a developing egg cell (oocyte) during the menstrual or estrous cycle. Upon maturity, it ruptures to release the oocyte during the process of ovulation.

2. Occurrence in Mammals:
Graafian follicles are a characteristic feature of the mammalian reproductive system. They develop within the cortex of the mammalian ovary under the influence of gonadotropic hormones such as Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

3. Analyzing the Options:
- Ovary of frog: Frogs are amphibians and do not form mature Graafian follicles in their ovaries.
- Testis of mammal: Testes are the male reproductive organs responsible for producing sperm and testosterone, so they do not contain follicles.
- Thyroid of mammal: The thyroid is an endocrine gland that contains thyroid follicles (which produce thyroid hormones), but these are completely different in structure and function from Graafian follicles.
- Ovary of mammal: This is the specific location where Graafian follicles undergo maturation and ovulation. Therefore, Graafian follicles are characteristically found in the ovary of a mammal.