Showing through the peritoneum, a much convoluted, white tube can be seen on the ventral surface of the kidney. This is the _mesonephric_ or _Wolffian duct_. In young specimens it may be nearly straight, lying near the medial border of the kidney. In adult specimens it can be followed forward as far as the anterior end of the testis. While the Wolffian duct is the duct of the kidney, and is joined by tubules of the anterior part of the kidney, it is so modified in the male that its principal function is to serve as the duct of the testis, a _vas deferens_. The collecting tubules of the posterior part of the kidney join to form a _urinary duct_ which is independent of the Wolffian duct. The posterior end of the Wolffian duct is straight and considerably expanded, forming a large _seminal vesicle_. The duct becomes more and more closely convoluted as it passes forward, and the kidney tissue overlying it diminishes. At the anterior end of the mesonephros the Wolffian duct forms a mass of tubules, the _epididymis_. Very small tubules, the _vasa efferentia_, pass from the anterior end of the testis to the epididymis. These are difficult for the student to distinguish. Cut through the peritoneum along the outer side of one kidney. Then strip the peritoneum toward the inner border of the kidney. The urinary duct will usually be closely attached to the peritoneum and parallel with the Wolffian duct, but nearer the midline of the body. The urinary duct can be separated from the peritoneum by a little careful work. Numerous small ducts pass from the kidney into the urinary duct. Open the uro-genital papilla near its tip and extend the incision forward so as to open the sac connected with the base of the papilla. The pore at the tip of the papilla leads into a space within the papilla itself, the _uro-genital sinus_, which branches to the left and right in pouches which extend beyond the posterior ends of the vasa deferentia. These cornua of the uro-genital sinus are of variable length, and are often named sperm-sacs. In a mature male they may be found to be filled with sperm, as may also the seminal vesicles and the convoluted portion of the Wolffian duct. The openings of the vasa deferentia into the sinus are large and easily located. The urinary duct opens into the sinus by a separate pore just behind the opening of the vas deferens. Cut open the seminal vesicle and part of the convoluted vas deferens. The space within is subdivided by transverse folds or lamellae extending from a longitudinal ridge. No vasa efferentia can be distinguished in Eugaleus. The anterior extremities of the kidney and testis of each side come into close contact with each other and here the vasa efferentia pass from the testis to the vas deferens. The sperm-sac is a large blind pouch, one or two inches in length, leading out of the posterior end of the vas deferens, and directed forward along its side. The vas deferens of Eugaleus is not convoluted.