Introduction: Although there is growing knowledge about the testicular capsule and rete ducts in mammals, very little information in other vertebrates is available. The only developmental study on the rete testis of ratite birds including ostrich has carried out by Budras and Meier (1981). Methods: Fertile ostrich eggs were incubated for 20, 26, 36 and 42 days then testicles of male embryos were separated and their 5-μm paraffin sections were stained by H&E, PAS, Masson’s trichrome and alcian blue. Images were captured by a light microscope equipped with digital camera. Results: 20-d-old embryo: There were some lacunar ducts in the attachment site of testis and kidney, while testicular capsule was limited to a covering epithelium and its underlying blood vessels. 26-d-old embryo: A loose connective tissue (tunica albuginea) appeared in the capsule while some organized cell aggregations were trapped inside it. These aggregations situated in the larger cisterns and in some areas they were transforming to tubule or duct-like structures. 36-d-old embryo: Tunica albuginea approximately changed to a dense connective tissue and majority of duct-like structures transformed to the capsular rete ducts. 42- d-old embryo: Tunica albuginea became completely dense and its meandering rays, defective septa, penetrated the interstitial tissue while holding some blood vessels. Conclusion: Tunica albuginea emerges in later embryonic stages while intracapsular rete ducts coordinately develop inside it. Capsular rete ducts in newly hatched chickes like the juvenile ostrich are spread along the capsule from orchido-epididymal border to the free surface of testis and their probable function is participating in semen transit.

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