REPRODUCTION. 411 



urethra, and is made up of numerous branched, glandular tubes 

 supported by connective tissue and unstriated muscular tissue. 



The penis consists of erectile tissue, which forms the corpus 

 spongiosum and the two corpora cavernosa, and it contains the 

 urethra ; the erectile tissue is made up of a mesh work of elastic and 

 muscular tissue into which arterioles open directly, the blood escaping 

 into veins. When the muscle fibres are relaxed the spaces become 

 distended with blood, causing erection of the organ. 



The formation of spermatozoa begins at puberty, and each sperma- 

 tozoon consists of a head, body, and tail, and is actively motile. The 

 fully formed spermatozoa pass from the testis into the epididymis and 

 vas deferens, and so to the seminal vesicles. 



FEMALE REPRODUCTIVE ORGANS. 



The female generative organs are the ovary, Fallopian (uterine) 

 tubes, uterus, and vagina. 



The Ovary is a solid organ composed of fibrous tissue (stroma), with 

 many spindle-shaped cells, and is covered by a layer of cubical cells 

 called the germinal epithelium. Groups of interstitial cells are found 

 in the stroma, similar to those which occur in the testis. The ovary 

 contains many vesicles of varying size (Graafian follicles), and a large 

 number of primordial follicles ; the latter are formed during foetal life 

 from down-growths of the germinal epithelium into the stroma, and 

 each consists of an ovum surrounded by a layer of flattened cells. 



The ovum is a large spherical cell enclosed in a striated envelope 

 called the zona pellucida (striata ); its protoplasm, which is abundant, is 

 filled with fatty and albuminous granules, and contains a spherical 

 nucleus (germinal vesicle) and nucleolus. 



At puberty some of the primordial follicles develop into Graafian 

 follicles (vesicular ovarian follicles). The epithelial cells covering the 

 ovum multiply to form a mass in which fluid appears, separating the 

 epithelium into two parts, an outer layer, the membrana granulosa, form- 

 ing the wall of the follicle, and an inner layer, the discus proligerus, sur- 

 rounding the ovum. At this stage the whole follicle is enclosed in a 

 fibrous capsule derived from the stroma. As the amount of fluid in- 

 creases, the follicle approaches the surface of the ovary, and eventually 

 bursts, the ovum being set free and passing into the Fallopian tube. 

 The process just described is called ovulation. The space left by the 

 escape of the ovum and fluid is filled up by the ingrowth of vascular 

 processes frofn the surrounding tissue, forming the corpus luteum, so 

 called because its cells are yellowish in colour owing to the presence of 



