The embryologic origin of the caput epididymidis in the rat.

The ACI rat with its known incidence of ipsilateral agenesis of the kidney and ductus deferens provides an excellent mammalian model for the study of the embryologic origin or the caput epididymidis. Because a portion of the caput epididymidis remains in these affected animals, it seems to be derived from the mesonephric tubules rather than the mesonephric duct in the rat. Histochemical assays also support the common origin of both the ductuli efferentes and caput epididymidis from the mesonephric tubules.