_Structure._—The testicle is surrounded by a thin fibrous capsule, which, in the mature cock, is very vascular. This capsule sends into the interior of the gland, septa which form the framework, or supporting structure. This framework forms the spaces in which are located the glandular substance. The glandular portion consists of the _tubuli seminiferi_, which are lined with cubical cells. The framework supporting these tubules gives passage to arterial branches of the spermatic artery, which furnish an abundant blood supply; the framework also supports the veins returning the blood from the testicle. The seminiferous tubules end in blind extremities in the epididymus or globus minor, and unite in the seminiferous canals. All arteries, veins, lymphatics, and seminiferous tubules enter or leave through the globus minor at the attached portion of the testicle. The _epididymis_ is made up largely of convoluted tubules which are the continuation of the secreting tubules of the globus major. The walls of the tubules of the globus minor become thicker and are provided with smooth muscle cells in addition to the connective tissue and endothelial lining. The convoluted tubules empty into the vas deferens. The epididymus is covered by the fibrous capsule; which corresponds to the tunica albuginea of mammals and may be considered as a reflection or modification of the visceral peritoneum. The substance of the testicle is very soft; in fact, it may be said to be of the consistency of encephaloid material. It is made up of secreting tubules in which are found the spermatozoa; it also contains cells which produce an internal secretion, or hormone. There is also produced some fluid in which the spermatozoa float, the whole material manufactured constituting the semen. The _spermatozoa_ of the fowl are provided with long cylindrical bodies, which may be straight or wavy (Fig. 55, _A_). The body of the spermatozoon is obtuse anteriorly, and posteriorly, tapers into a filimentary tail, or flagellum, of varying length, by the aid of which the spermatozoon moves about in the fluid. The histological structure of the testicles of the baby chick at hatching is approximately one-half white fibrous connective tissue. The seminal tubules are small and widely distributed among the connective tissue. The cells of these tubules possess rather large nuclei, round in shape, with linin network and chromatin granules, typical of resting germ cells. As the bird develops the testicles grow, the seminal tubules become larger, and the amount of connective tissue correspondingly less. [Illustration: FIG. 55. _A._ Spermatozoa of a cock. _a_, The spermatozoa. _b_, The head. _c_, The tail. _B._ The oviduct of a hen removed. _A_, The oviduct. _B_, The superior ligament. _C_, The inferior ligament. Note the oviduct thrown in folds and the anastomosing blood-vessels. ]