REPRODUCTION IX MAN 1369 



pregnancy. The bijr corpus luteum found in pregnancy is often 

 spoken of as the ; true ' corpus luteum, and is distinguished from the 

 corpus luteum spurium of menstruation or of ovulation without 

 fertilisation. There is, however, no essential difference other than that 

 of size between these two kinds of corpus luteum. It must not be 

 imagined that all the 70.000 primordial follicles found in the ovary of 

 a new-born child undergo this series of changes ; it is probable that in 

 the human female ovulation occurs, as a rule, once every four weeks 

 during the thirty-five years of sexual life. A vast number of the 



FIG. 560. Fully developed corpus luteum of the mouse. (SoBOTTA.) 



Graafian follicles, after developing to a certain extent, undergo 

 regressive changes, both during childhood and during adult life. The 

 cellular elements degenerate, leucocytes wander into the follicle and 

 attack the degenerating ovum, so that finally the follicle is replaced 

 by connective tissue, without the formation of any corpus luteum. 



MENSTRUATION. Puberty in the girl is marked by the onset of 

 menstruation. Under this term is understood a flow of blood and 

 mucus from the uterus, which recurs every four weeks and lasts each 

 time from four to five days. Before the first menstrual period, other 

 signs of puberty, i.e. of approaching sexual maturity, are usually 

 observed. These include rapid growth, with changes in the skeleton, 

 leading to the typically feminine type of pelvis, a development of 

 the mammary glands, and the growth of hair on the pubes. At the 

 same time there is increased development of the mental characteristics 



