Objectives: Despite some studies on ostrich testes there is no clear information about anatomical and histological development of testes in ostrich embryo and newly hatched ostrich chick. The aim of the study was to provide this information. Materials and Methods: Fertile ostrich eggs were obtained and incubated for 20, 26, 36 embryos and one-day-old chick. Testes was separated from kidney and immersed in bouin’s solution. 5μm thick paraffin sections were prepared and stained with H&E, PAS and Masson trichrome stains for histological observation by light microscope. Results: In 20-d-old embryo, testes with a dirty white color were located in the ventral surface of mesonephros kidneys. In 26-d-old embryo testes are brighter and more distinguishable from kidney in texture and color. In 20-d-old embryos aggregations of Sertoli cells corralled some primordial germ cells (PGCs). In 26-d-old embryos Sertoli cells aggregations were more regular and more similar to shape of cord. PGCs are clearly increased relative to 20-d-old embryos. In 36-d-old embryos external coat in all sides was a thin tunica albuginea. Sertoli cell aggregations were completely replaced by organized sex cords. Precursors of Leydig cells were also present in the interstitial tissue. In 1-d-old chick cover of testis had smooth surface. The sex cords still had no lumen. Sex cords had many PGCs that tend toward the basement membrane. Interstitial tissue had mesenchymal cells and Leydig cells. Conclusions: Ostrich testes like other avian species are located in the abdominal cavity at the ventral side of the kidneys. Probably define number of PGCs inter to each testis and surround by mesenchymal cells that are progenitors of the sertoli cells. Forming of primary sex cords commences before day 20 of embryonic period, whereas forming of tunica albuginea and complete separation from kidney structures starts later. At one day old chick in spite of expanding in testis volume it sounds not to increase in number of mitotic germ cells. At this time leydig cells appear in single.

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