In the young specimens usually supplied to laboratories the vas deferens is straight and no seminal vesicle is developed. The vasa efferentia are more difficult to see; otherwise the relations of the urinary and genital organs are as in the adult.
The suspensory ligament of the liver is continued posteriorly along the midline of the ventral body wall; the dorsal edge supports a funnel which opens into the abdominal cavity by a long, narrow mouth. From the anterior end of the funnel two narrow tubes pass to the right and left over the anterior surface of the liver. They end blindly in the tissues dorsal to the anterior end of the liver. These are vestiges of the Muellerian ducts (pronephric ducts) which form the oviducts of the females.
The female. The ovaries are large, white bodies lying at the sides of the stomach, dorsal to the lobes of the liver. Each is covered by the peritoneum and suspended by a fold of the same, the mesovarium. Ova of various sizes may be felt in the tissue of the ovary, which should be exposed by dissection.
The ovaries of Eugaleus are long slender bodies lying on either side of the mesogaster, dorsal to the stomach and intestine. Their posterior portions are fused.
The oviducts (Muellerian ducts) are large tubes suspended from between the kidneys by a narrow peritoneal band. The posterior portion of the oviduct, where development of the eggs takes place, is considerably enlarged. Each oviduct opens separately into the cloaca by a pore at the side of the urinary papilla. Followed forward, the oviducts pass over the anterior surface of the liver and following a continuation of the suspensory ligament, bend around posteriorly and unite. At the point of union they open into the coelom by a common, large, funnel-shaped aperture, the ostium tubae.
Cut through the peritoneum along the outer side of one kidney. Then strip the peritoneum toward the inner side of the kidney. Numerous small excretory ducts will be seen joining the main urinary duct (Wolffian duct, mesonephric duct), which runs along the inner margin of the kidney. Make an incision in the side of the urinary papilla to open the cavity within it, the urinary sinus. The connection of this with the pore at the tip of the papilla should be demonstrated. Extend the incision forward. The urinary sinus divides into right and left cornua which are of considerable size and lie dorsal to the oviducts. Trace the Wolffian duct to the urinary sinus and demonstrate its opening into the cornu anterior to the point where the two cornua unite.
In young specimens the ovaries are small, and the oviducts are narrow, white tubes lying along the medial margins of the kidneys.
Nephrostomes, short, segmentally arranged kidney tubules which open to the coelom by a funicular aperture, are found by a close examination along the medial border of each kidney. They should be observed carefully with the aid of a good dissecting lens. Learn the significance of these structures.
In the course of development two sets of nephridia (kidneys) are formed. The first (pronephros) develops just back of the head of the embryo, but does not persist in the adult. Its duct, known commonly as the Muellerian duct, develops into the functional oviduct of the female, but forms an apparently useless vestige in the male. The second kidney (mesonephros) develops behind the first and is the excretory organ of the adult. Its duct (frequently given the name of Wolffian duct) is the urinary duct in the female, but functions in the male chiefly as a sperm duct, and therefore is called the vas deferens. The collecting tubules of the posterior portion of the kidney of the male unite to form a urinary duct which opens into the Wolffian duct or the uro-genital sinus.