COORDINATION 



439 



within the body cavity as are their counter- 

 parts, the ovaries. 



Radiations of various kinds, such as 

 x-rays, if given in large doses have a lethal 

 effect upon the sperm-producing portion of 

 the testis. In smaller doses the eflfect may be 

 simply to alter the genes which ultimately 

 might produce far greater casualties in the 

 human race than mere sterility in a few 

 individuals. At any rate, people who work 

 around x-ray machines must guard them- 

 selves carefully or they will become sterile, 

 although none of their secondary character- 

 istics will be affected. 



Chemically, testosterone is well known 

 and is found to be similar to one of the 

 female hormones. Other related testicular 

 hormones are collectively called androgenic 

 compounds and seem to be generally dis- 

 tributed throughout the body. They are 

 probably substances which are utilized in 

 the production of testosterone or they are 

 products of its breakdown, because they 

 are found in the urine. 



After the testes had been associated with 

 male vigor, the intriguing idea of trans- 

 planting them or injecting their extracts 

 into the body of a senile male caught the 

 imagination of early biologists. Long ago, 

 Brown-Sequard, a famous physiologist, in- 

 jected himself with testicular extracts 

 which he professed renewed his vigor. This 

 initiated a long series of such experiments 

 both on animals and on man himself. The 

 results have all been disappointing, and 

 today it is believed there are no beneficial 

 effects from either the administration of 

 testosterone or the grafting of testes. It can 

 be concluded that testosterone does initi- 

 ate and maintain the secondary sexual char- 

 acteristics and probably contributes to sex- 

 ual behavior and urge. In man, however, 

 the latter function is so complexly inter- 

 woven with psychological reactions that it 

 is difficult to determine just how much 

 effect it really has. 



The ovary. A far more complex battery of 

 hormones is produced by the mammalian 



Fig. 16-31. A Graafian, follicle from a rat, sectioned to 

 show the egg. 



female generative apparatus than by the 

 male. This is due to the recently acquired 

 though intricate mechanism of caring for 

 the developing embryo, both before birth 

 and immediately thereafter. These hor- 

 mones are produced in the ovary, although 

 others probably occur in various parts of 

 the genital tract. 



At birth and throughout the early life of 

 a female the potential eggs lie dormant in 

 the outer region of the ovary. From puberty 

 on they begin to grow. As an egg grows, 

 there develops about it a fluid-filled space, 

 and the entire structure is called a Graafian 

 follicle (Fig. 16-31). These follicles pro- 

 duce a hormone, estrogen, which is the 

 counterpart of testosterone in the male. The 

 influence of estrogen in the blood stimu- 

 lates the onset of changes both in body con- 

 tours and in the female organs which finally 

 result in the mature human female. A 

 similar situation occurs in all mammals. 

 Before completion of maturity occurs, an- 

 other hormone, progesterone, must be pro- 

 duced by a special part of the ovary called 

 the corpus luteum. After the rupture of the 

 Graafian follicle and the liberation of an 

 egg (Fig. 16-31), the cavity left fills with 

 this tissue which, in turn, produces pro- 



