2l8 THE UROGENITAL SYSTEM 



of an inner, vascular tunica interna and an outer, fibrous and muscular 

 tunica externa. 



Fully formed Graafian follicles are found in the ovaries during the 

 second year and they may be even present before birth. Ovulation may 

 occur at this time, but usually these precociously formed follicles degen- 

 erate with their contained ova. Thus, although thousands of ova are 

 produced in the ovary, comparatively few are set free ready for fertiliza- 

 tion during the sexually active life of the female, from puberty to the 

 climacteric period, or menopause. The details of ovulation and its rela- 

 tion to menstruation has been discussed on p. 10. 



The Corpus Luteum. After ovulation, a blood clot, the corpus hemorrhagicum, forms 

 within the empty follicle. The follicle cells of the stratum granulosum proliferate, enlarge, 

 and produce a yellow pigment (R. Meyer, 1911). The whole structure, composed of 

 lutein cells and connective tissue strands, is termed the corpus luteum, or yellow body. 

 The blood clot is resorbed and replaced by fibrous scar tissue, white in color, known as 

 the corpus albicans. If pregnancy does not intervene, the corpus luteum spurium reaches 

 its greatest development within two weeks and then degenerates. In cases of pregnancy 

 the corpus luteum verum continues its growth until, at the thirteenth week, it reaches a 

 maximal diameter of 15 to 30 mm.; at birth it is still a prominent structure in the ovary. 

 It is believed to produce an important internal secretion, for if the corpus luteum is re- 

 moved the ovum fails to attach itself to the wall of the uterus, or if already embedded, de- 

 velopment ceases (Fraenkel). An influence in retarding ovulation and stimulating the 

 mammary gland function has also been shown experimentally (L. Loeb; O'Donoghue). 



Comparison of the Testis and Ovary. -It is clear that the superficial 

 epithelium, after forming the inner epithelial mass, takes no further part in 

 the differentiation of the testis and only a small part, if any, in that of the 

 ovary. The testis cords, rete testis, and tunica albuginea differentiate 

 early from the inner epithelial mass. The inner epithelial mass of the 

 ovary develops slowly and passively being divided and moulded by 

 actively ingrowing connective tissue. The Graafian follicles are not the 

 homologues of the testis cords, and the tunica albuginea appears late. 

 The rete ovarii corresponds to the rete testis, but remains a rudimentary 

 structure. 



Anomalies. Congenital absence or duplication of the testes and ovaries is very rare. 

 Fused testes and lobed ovaries are also known. 



Teratomata. These peculiar tumor-like growths occur rather frequently in the ovary, 

 less often in the testis and other regions. The simpler types, caller dermoid cysts, contain 

 ectodermal derivitive such as skin, hair, nails, teeth, and sebaceous glands. They grade 

 into complexes consisting of organ-like masses, from all three germ layers, intermingled 

 without order. Misshapen representatives of all tissues and organs may be present. 

 Among other explanations of the cause, the isolation and subsequent faulty development 

 .of blastomeres has been advanced. 



