Abstract: Histological studies on the structure of Testes and Vasa deferens and Spermatophores has been clearly explained in a marine water prawn Penaeus indicus in two different stages like mature and fully mature stage . The reproductive system of male has the following reproductive organs such as Testis, Vas deferens and an Ejaculatory duct. A pair of testis looks like lobes and white in colour, vas deferens is divisible into Proximal , Middle and Distal parts. The Proximal vas deferens (PVD) is a thin tube coming out from the posterior part of the testis. The middle vas deferens (MVD) is slightly broad in the anterior part , flattened and folded at its posterior part. Distal vas deferens (DVD) is the small and cylindrical tube. The vas deferens which passes the spermatophores to the ejaculatory duct .The Distal vas deferns is the smallest portion and it was slightly bulged at the base of the ejaculatory duct . The functions of the ejaculatory duct is to release the spermatophores into the thelycum of female reproductive organ.