Abstract: 【Objective】The main purpose of this study was to study the tissue structure and morphological development process of hair follicles in Subo Merino sheep, and results of the study will lay a histological basis for further resolving the molecular regulation mechanism of hair follicle development of fine-wool sheep. 【Method】The histological characteristics of ten different parts of skin, such as (the poll, midside of neck, up side of neck, wither, back, midside of body, shoulder, belly, sacrum and femur, respectively) of Subo Merino sheep fetuses on the 65, 85, 105 and 135 day of gestational age were analyzed using paraffin section methods. 【Result】 The results showed that the hair follicle structure of Subo Merino sheep was in the same manner compared with other animals, which was composed of hair bulb, connective tissue sheath, outer root sheath, inner root sheath and hair shaft. At the embryonic age of 65 days，primary follicles has been formed hair germs, with the extension of the hair germs, and continue depth into the dermis, the columnar structure was formed. The cap-like structure was formed by the aggregation of a large number of dermal cells at the end parts; at this stage, the epidermis of each part were formed a complete structure. At the embryonic age of 85 days，the upper part of the hair follicle formed bulge, formed hair cone structure above the dermal papilla, hair bulb was basically formed, and the length of the hair papilla was larger than the width; the vesicle structure of the secondary follicle could be found at the bottom of the primary hair follicle, and also the original sebaceous cell were found. A great quantity of secondary follicles were formed at the embryonic age of 105 days; along with the extension of the primary follicles, secondary follicles inserted into the dermis layer, the diameter of the dermal papilla was gradually increased and sebaceous glands began to form; the secondary-derived follicles began to differentiate from the neck carina of the original secondary follicles, sweat gland and hair canal could also be found, and formed a complete hair follicle group structure, trio group was dominant; each hair follicle group was composed of 1-3 primary follicles and several secondary hair follicles surrounding it. A large number of secondary-derived follicles were formed at the embryonic age of 135 days, formed mature sweat glands, most of primary follicles and some of secondary hair follicle had matured at this stage, hair follicle formed a keratinizated hair shaft and emerged through the epidermis.【Conclusion】 It can be inferred from the experiment that primary follicles of embryonic skin in Subo Merino sheep began to form about 50-55d; gestational age of 65-75 days are an important period for forming of primary follicle; gestational age of 80-85 days are the formation period of secondary follicle, in this period, a great number of primary follicles were formed; a great deal of secondary follicles were differentiated at the gestational age of 105-135 days, this is the critical period of the formation and development of secondary follicles. This study described the hair follicle structure and the whole formation process of hair follicles from occurrence to maturity of Subo Merino sheep and provide a reference information for the related field researchers.

Key words: Subo Merino sheep, hair follicle structure, morphogenesis, primary follicle, secondary follicle, secondary-derived follicle