ABSTRACT
The smooth muscles of the ductuli efferentes and ductus epididymidis develop from primitive mesonephric mesenchyme.
In both ductuli efferentes and ductus epididymidis a proliferation and condensation of the mesenchyme occurs around the ductuli and epididymal duct. This appears in the ductuli efferentes of the 14- and 15-day rat embryo, and by birth it has extended to the cauda epididymidis.
Subsequent to the condensation around the ducts, elongation of the mesenchymal cell nuclei beings, and the cytoplasm becomes aligned and extended. This appears first in the circular layer of the caput by the 16th day of gestation, and in the investing layer of the corpus epididymidis by the 20th day. Formation follows lastly in the region of the cauda epididymidis, occurring by parturition or very soon thereafter.
After the smooth muscle cells are differentiated, delicate pulsations or contractions may be observed in the ductuli efferentes and ductus epididymidis. They can be seen first at 17 days of gestation in the region of the coni vasculosi, where they occur at intervals of 60 sec. This condition may not be representative of all 17-day embryos as contractions were seen in but three of thirty-three preparations studied.
Rhythmic movements of the ductuli and upper and middle caput epididymidis take place with regularity, occurring approximately at 40-45 sec. intervals in the ductuli and upper caput and at 20-25 sec. in the middle caput epididymidis at birth.
By the 10th day, a visible contractile wave commences in the region of the ductuli and passes to the upper corpus where it disappears.
Inspection of contraction frequency data for the ductuli and upper segments of the epididymis indicates that the interval between successive rhythmic waves diminishes with age.
An incidental examination of the Müllerian duct of female neonatal and post-natal animals demonstrated that rhythmic contractions are established by birth.