An in ovo experimental study of mesonephric mesenchyme—Wolffian duct relationships has been performed with special reference to the progression and the ramification of the Wolffian duct in quail—chick and quail—duck associations. Two methods are used to obtain chimaeric mesonephros in ovo. First, a piece of a quail blastoderm containing the tip of the Wolffian duct is grafted on to a chick blastoderm behind an obstacle. The obstacle is a small piece of shell membrane and it prevents the migration of the chick Wolffian duct. Second, chimaeric blastoderms are made by associating in ovo halves of quail blastoderm (anterior or posterior) with the complementary halves of chick or of duck blastoderms. The experiments are performed in such a way that the Wolffian ducts are in the anterior part and the nephrogenic blastemas in the posterior part. In those experiments in which a Wolffian duct of one species is associated with the mesonephric mesenchyme of another, the Wolffian duct grows backward above the intermediate cell mass without any participation of the heterospecific cells. In quail-duck associations, the Wolffian duct reaches the cloaca and buds off the ureteric diverticulum later than it does in quail—chick associations.
The mesonephric mesenchymal area induces the Wolffian duct to branch out into a collecing system. Quail Wolffian duct gives rise to more numerous collecting tubules than does the chick Wolffian duct. In quail mesenchyme—chick Wolffian duct mesonephros, the collecting tubules are not always present and often the tubules derived from the mesenchyme invade the wall of the Wolffian duct. In all cases only very short collecting tubules are derived from the Wolffian duct.