GROWTH AND REPRODUCTION 



767 



tissue, which, under the influence of dilator nerves, becomes engorged 

 with blood, leading to the erection of the organ. The urethra passes 

 through the corpus spongiosum of the penis. 



The period of sexual life begins in the male with the onset of 

 puberty, and continues more or less throughout life. There is un- 

 doubtedly a decline in fertility in the later years of life, but it is not 

 uncommon for men of seventy or even eighty years of age to become 

 the fathers of children. 



The Reproductive Processes in the Female. The sexual apparatus 

 of the female consists of the egg-bearing organ, or ovary, in which 

 the eggs are matured, and the womb, or uterus, in which the foetus 

 is developed from the fertilized ovum, or oosperm. Accessory to 

 these are the oviducts, or Fallopian tubes, which conduct the egg 



GERMINAL EPITMELH.I 



FTONICA ALBUGINEA 



'LUMN of 



RMINAL EPITHELIUM /.7, 



ISOLATED NEST 



PENINO OVUM ^ 



'GERMINAL SPOT 

 OVUM 

 'OlSCUS PROLIGERUS 



FIG. 473. DIAGRAMMATIC SECTION OF FIG. 474. RIPE GRAAFIAN FOLLICLE 

 OVARY OF FIFTH-MONTH FCETUS, AT PUBERTY. (Keith.) 



SHOWING NESTS OF GERMINAL EPI- 

 THELIUM AND UNRIPE GRAAFIAN 

 FOLLICLE. (Keith.) 



to the uterus, and the vulva and vagina, by means of which the male 

 element is introduced into the female, and through which the full- 

 time foetus is passed into the world. 



The ovary consists of (1) the germinal cells, which by maturation 

 provide the female gametes, the ova; (2) the interstitial cells, which 

 furnish an internal secretion concerned in the development of the 

 secondary female characteristics (see p. 506). A fibrous stroma 

 carries the bloodvessels, lymphatics, and nerves, which supply the 

 organ, and its cellular elements form the so-called interstitial cells 

 which produce the internal secretion. The cells of the germinal epi- 

 thelium lie just beneath the external capsule the tunica albuginea. 

 These divide to produce the oogonea, which, in developing into oocytes, 

 gradually sink inwards into the stroma and are surrounded by a 

 layer of stroma cells. Thus is formed an immature Graafian follicle. 

 Eventually the stroma cells divide to form a layer round the oocyte 

 and a layer of cells which surround the follicle. These two layers 



