Wolffian tubules

The Wolffian tubules (or Kobelt's tubules) are precursors of the mesonephros.

Development
On the medial side of the Wolffian duct, from the sixth cervical to the third lumbar segments, a series of tubules, the Wolffian tubules, develops. They increase in number by outgrowths from the original tubules. The change from solid masses of cells to instead become hollowed in the center. One end grows toward and finally opens into the Wolffian duct, the other dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus.

The tubules collectively constitute the mesonephros.