THE REPRODUCTIVE ORGANS. 217 



coat is a layer of areolar tissue connecting the vagina with the 

 neighboring parts, except at its posterior and upper part, where it 

 is covered with a serous membrane, forming part of the peritoneum. 



5. The External Genitals. The hymen is a fold of the mucous 

 membrane, and consists of fibrous tissue with a covering of strati- 

 fied epithelium. The same general structure obtains also in the labia 

 minora, prepuce, and labia majora ; but the labia minora and prepuce 

 are destitute of fat, while the labia majora contain considerable adipose 

 tissue. All three organs are supplied with sebaceous glands, Avhich 

 are numerous beneath the prepuce and are associated with hairs only 

 on the labia majora. The latter also contain fibres of smooth mus- 

 cular tissue, corresponding to the analogous dartos of the scrotum. 

 The bulbi vestibuli, crura of the clitoris, and the body and glans of 

 that organ are composed of erectile tissue. The glands of Bartholin 

 are compound racemose glands, in which the alveoli are lined with 

 a columnar epithelium resembling in structure that of the mucous 

 glands in other parts of the body. The epithelium lining their 

 ducts is of the cubical variety. 



The parovarium is a remnant of the Wolffian body of the foetus, 

 consisting of a series of blind tubules lined with epithelium (Fig. 

 185). It is situated between the Fallopian tube and the ovary. The 

 remains of the Wolffian duct and of the duct of Miiller, having a sim- 

 ilar structure to the tubules of the parovarium, are sometimes per- 

 sistent, the one connected with the parovarium, the other with the 

 extremity of the Fallopian tube. These structures are of interest 

 because tumors occasionally arise from them. 



The Maturation of the Ovum. Before the ovarian ovum is ready 

 for fertilization it must undergo two divisions, during which the 

 amount of chromatin left in the mature egg is reduced one-half. 

 The first division results in the formation of two cells, which differ 

 enormously in the amount of cytoplasm they possess, but which 

 have equal shares of the chromatin in the original nucleus. The 

 smaller of these two cells is known as the " first polar body." After 

 its separation from the larger cell both cells divide again, without 

 an intermediate growth of the chromatin. In this second division 

 of the larger cell the two resulting cells are again very unequal 

 in size, the smaller being the " second polar body." The first polar 

 body having also divided, there result from these successive divis- 

 ions one mature egg and three polar bodies, each with only half 

 as many chromosomes in its nucleus as are commonly found in the 



