The interstitial endocrine cells that produce testosterone are located the interstitial endocrine cells that produce testosterone are located lining the ductus deferens between the seminiferous tubules in the rete testis in the epididymis

The answer is

Testicles

Explanation:

Interstitial cells of Leydig, also known as Leydig cells are found adjacent to the seminiferous tubules inside the testicle of male species. They produce secretions known as testosterone in the presence of luteinizing hormone (LH). These cells are polyhedral in shape displaying a large prominent nucleus, an eosinophilic cytoplasm and numerous lipid-filled vesicles.

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