Differentiation of the gonads
The gonads arise from two very different kinds of cells that originate in the embryo:
·The primordial germ cells (PGC) will form the gametes (sperm cells and oocytes). Which are originated from the ectoderm,

·The somatic cells are supporting cells responsible in nourishment which surround the primordial germ cells and form the somatic gonadal blastema.
                            − In the testes the supporting cells (Sertoli) and the interstitial cells (Leydig) are involved. 
                            −   in the ovary the follicle cells and the theca cells.         
Differentiation of Testes
·The testes differentiate themselves earlier than the ovaries, namely in the course of the 7th week which is controlled by the SRY gene on the Y chromosome that induces the development of the testes through the activation of a series of further genes.

·Development of the parenchyma, the differentiation of Sertoli's supporting cells form the first step in the organogenesis of the testes.

·Development of the stroma, the mesenchyma between the testicular cords congeals and forms connective tissue septa that subdivide the testicles into lobules. Also, the mesenchyma forms a taut connective tissue layer between the testicular cords and the coelomic epithelium as well as the future tunica albuginea.

·In the testicular cords PGC (future spermatozoa) are to be found. The somatic cells differentiate themselves into Sertoli's supporting cells, responsible for nourishing the spermatozoa and secreting the antimüllerian hormone (AMH), which promotes the atrophy of the paramesonephric duct (Müller).

·The rete testis forms the continuation of the centrally-lying testicular cords or the straight seminiferous tubules.

·The efferent tubules connect the rete testis with the mesonephric duct (Wolff), the future epididymis, which continues with the deferent duct.

·The interstitial mesenchymal cells of the testes develop into Leydig's interstitial cells. They are responsible for the production of testosterone that, among other things, assures that the mesonephric duct (Wolff) does not atrophy.

·The stroma, made of connective tissue, subdivides the testes into lobules and forms the tunica albuginea.

Descent of the Testes

Between the 3rd month of pregnancy and its end the testes become transferred from the lumbar area (ventro-medial to the mesonephros) into the future scrotum. This transfer is due to a combination of growth processes, hormonal influences. and gubernaculum testis. The gubernaculum testis arises in the course of the 7th week from the lower gubernaculum, after the mesonephros has atrophied. Cranially it has its origin at the testis and inserts in the region of the genital swelling (future scrotum).
At the same time, at the inguinal canal along the lower gubernaculum, an evagination of the peritoneum arises, the vaginal process, on which the testes will slide through the inguinal canal. The vaginal process lengthens downwardly, it takes the muscle fibers of the oblique internal muscle and the transverse muscle with it. The muscle fascia of the transverse muscle is the innermost layer and in the scrotal region, it forms the internal spermatic fascia of the spermatic cord and the scrotum. The muscle layer of the musculus cremaster is formed from fibers of the oblique internal and transverse muscles. Externally, the external spermatic fascia is formed from the superficial aponeurosis of the oblique external abdominal muscle.