Development of the gonads
Via the rete testis, the seminiferous tubules become connected with outgrowths from the mesonephros, which form the efferent ducts of the testicle.
Later the mass is differentiated into a central part, the medulla of ovary, covered by a surface layer, the germinal epithelium.
The immature ova, in turn, are carried into the stroma beneath by bud-like ingrowths (genital cords of the germinal epithelium).
During early embryonic development, cells from the dorsal endoderm of the yolk sac migrate along the hindgut to the gonadal ridge.
Oocytes (immature ova) residing in the primordial follicle of the ovary are in a non-growing prophase arrested state, but have the capacity to undergo highly efficient homologous recombinational repair of DNA damages including double-strand breaks.
In rare cases, the gubernaculum may fail to contract adhesions to the uterus, and then the ovary descends through the inguinal canal into the labium majus; under these circumstances, its position resembles that of the testis.
Via the rete testis, the seminiferous tubules become connected with outgrowths from the mesonephros, which form the efferent ducts of the testicle.
Such descent is ancestral in placental mammals with a derived condition of non-descent with testes remaining near the kidneys occurring in Afrotheria such as elephants.
[6] At an early period of fetal life the testicles are placed at the back part of abdominal cavity, behind the peritoneum, and each is attached by a peritoneal fold, the mesorchium, to the mesonephros.
This is at first a slender band, extending from that part of the skin of the groin which afterward forms the scrotum through the inguinal canal to the body and epididymis of the testicle.
As the testicles develop, the main portion of the lower end of the gubernaculum is carried, following the skin to which it is attached, to the bottom of this pouch.
It seems certain also that the gubernacular cord becomes shortened as development proceeds, and this assists in causing the testis to reach the bottom of the scrotum.
By the end of the eighth month, the testicle has reached the scrotum, preceded by the vaginal process, which communicates by its upper extremity with the peritoneal cavity.
Just before birth, the upper part of the vaginal process, at the internal inguinal ring, usually becomes closed, and this obliteration extends gradually downward to within a short distance of the testicle.
The process of peritoneum surrounding the testis is now entirely cut off from the general peritoneal cavity and constitutes the tunica vaginalis.
