THE FEMALE SEXUAL ORGANS 697 



It had long been supposed that menstruation was due to some nervous influ- 

 ence of the ovary over the uterus. But it has been observed that in monkeys 

 menstruation can take place even when the ovaries have been removed from 

 their normal position in the body and transplanted elsewhere, all nervous con- 

 nections with the ovary being severed. Hence it is not improbable that the 

 internal secretion of the ovary is the essential medium of influence (cf. page 358). 



Just as in man, the appearance of puberty in woman is marked by other 

 changes in the body: the mammary glands increase in size, the figure loses 

 its childish delicacy and, by the deposition of subcutaneous fat, becomes more 

 robust. Castration of the female (extirpation of the ovaries) likewise pro- 

 duces more or less sharply pronounced changes (cf. page 358). 



The monthly changes in the uterus proceed as follows : five to ten days 

 before the period of discharge the blood vessels of the mucous membrane 

 become dilated, the membrane itself as a result swells up and a proliferation 

 of its more superficial layers takes place. Then follows a hemorrhage in the 

 subepithelial tissue which is probably not due to rupture of blood vessels, but 

 to the escape from them of red blood corpuscles. The nutritive condition 

 of the mucous membrane thus becomes impaired, and as a consequence its 

 outermost layers (the decidua menstruaUs) slough off (according to some 

 authors the loss of the mucous membrane is not due to lack of nutrition, but 

 to pressure of the escaping blood in the subjacent tissues) ; the period of 

 discharge continues for about four days, when a process of restitution sets 

 in. These changes proceed by a regeneration of tissue from the remaining 

 epithelium and its invaginations, and last from five to ten days. Hence the 

 tissue changes accompanying menstruation cover all told from fourteen to 

 twenty-four days out of each month. 



The physiological significance of menstruation probably consists in a 

 preparation of the uterine wall for the reception of the fertilized ovum. 



Like the rest of the mucous membrane of the uterus, that of the cervix bears 

 on its surface a ciliated epithelium, invaginations of which form the cervical 

 glands. These glands secrete a clear, viscid mucus which collects in the cervi- 

 cal canal soon after conception and remains there as a plug serving to keep the 

 passage closed throughout pregnancy. 



After the climacteric has been passed, and ova are no longer being formed, 

 the mucous membrane of the uterus shrivels up, the connective tissue under- 

 lying it increases in quantity, the cervical glands atrophy, and the epithelium 

 loses its cilia. 



C. PREGNANCY AND BIRTH 



Spermatozoa are independently motile, and in virtue of this property of 

 motility can traverse great distances, relatively speaking. Their entrance into 

 the uterus and Fallopian tubes is due no doubt to some chemotactic influence 

 over them exercised by the secretions of those organs, and their ascent toward 

 the ovaries within the tubes is traceable to their rheotactic properties (cf. 

 page 56). Coming into contact with the ovum, the spermatozoon enters it, 

 possibly under the spell of a thigmotactic influence (cf. page 56). Inside the 

 ovum the spermatozoon produces changes comprehended under the term fer- 

 tilization, which make it possible for the ovum to develop into a new individual. 



