In addition to the tubules, the spermatogenic cells, and the connective tissue, there is also in the testicles more or less fat. There is a small amount of connective tissue between the seminiferous tubules, in which locations there are also clusters of polyhedral cells, with round nuclei, others are the interstitial cells. =The Vas Deferens= (Fig. 54, _D_). _Location and Shape._—Extending from the epididymus, is the vas deferens which runs backward on the infero-internal surface of the kidney and to the outside of the ureter. It is very tortuous passing on the infero-lateral surface of the kidney in company with the ureter and becoming somewhat expanded posteriorly it terminates in the upper wall of the cloaca in a rather small papilla located in the uro-genital portion of the cloaca anterior to the mouth of the ureter. This papilla is the organ of copulation and in ducks is very large, and spirally elongated, and retractile forming a kind of penis. The papilla is traversed by a furrow on the upper surface through which the semen flows. _Structure._—The vas deferens is covered and supported by the peritoneum. Its wall is made up of a fibrous structure in which may be found smooth muscle fibers. The wall does not possess glands. It is lined with columnar epithelium. The posterior end is expanded and terminates into a papilla. The base of the papilla is surrounded by a plexus of arteries and veins, which serve as an erectile organ during the venereal orgasm, when the fossa of the turgid papilla is everted, and the semen brought into contact with the similarly everted orifice of the oviduct of the female, along which the spermatozoa pass by undulatory movements of their ciliary appendage, or tail. THE FEMALE GENERATIVE ORGANS (Fig. 56) The female generative organs consist of one ovary and an oviduct. _Location._—The ovary is located similarly to the testicles of the male bird, in the sublumbar region of the abdominal cavity, just at the anterior end of the kidneys, posterior to the lungs, and slightly to the left of the center. _Shape._—In the pullet the ovarian mass appears somewhat like a bunch of grapes, being made up of from 3500 to 4500 small, whitish spheres, which represent the undeveloped ova, and which in the active state are developed, one by one, into yolks with their blastoderms. From the blastoderm the fetus may later be developed. In the active ovary of the laying hen the ovarian mass is of considerable size, as it contains ova in different stages of development. Only one ovum is completely developed at a time, though occasionally there may be only a few hours between the maturity of successive ova. The ova receives nourishment from the blood-vessels of the capsule, which vessels are branches of the ovarian artery. [Illustration: