DEVELOPMENT OF THE URINARY AND SEXUAL ORGANS. 999 



on either side a large cutaneous elevation (//, w) . At the end of the third month 

 there passes on the under surface of the genital eminence to the cloaca a groove, 

 on whose two sides distinct folds appear (//, r). In the middle of the third month 

 the cloacal orifice becomes divided, prolongations from above and from each 

 side insinuating themselves as the perineum (ra) between the urachus, which has 

 now become the bladder (Fig. 392, 5, 6), and the rectum (M). 



In the male (IV) the genital eminence now becomes large, and its groove closes 

 from the orifice of the bladder (the urachal orifice of the former cloaca) to the 

 apex of the eminence in the tenth week. The entrance to the bladder is thus 

 displaced to the apex of the genital eminence. Should this closure fail to take 

 place, either wholly or in part, there occurs the arrest of development known as 

 hypospadias. In the fourth month the glans is formed, in the sixth month the 

 prepuce; both are at first adherent. The cutaneous folds that unite in the raphe 

 form the scrotum. 



In the female (///) the undifferentiated condition of the original rudimentary 

 sexual organs remains, to a certain degree, permanent; the small genital eminence 

 becomes the clitoris, the genital folds the nymphae; the cutaneous folds remain 

 separate as the labia majora. The urogenital sinus remains short, as it was, 

 and it becomes the vestibule of the vagina; while in the male, through closure 

 of the genital groove, a long additional canal is formed. 



Hermaprodism. In rare cases the external genitalia persist in their original 

 undifferentiated rudimentary stage (somewhat as is shown in Fig. 393, //), con- 

 stituting an arrest of development. Under such circumstances an external 

 determination of sex is impossible (pseudohermaphrodism) . In isolated cases 

 there occurs the development on one side of male, and on the other side of female 

 internal organs of generation; the external genitalia are then not typically de- 

 veloped. Such cases are designated true lateral hermaphrodism. The condition 

 is not rare in swine, goats and beeves, but it has probably never been established 

 in man beyond all doubt. 



The cause of sexual development in one or the other direction has not, as yet, 

 been determined with certainty. From statistical data (80,000 cases) the influence 

 of the age of the parents has been established. If the husband is younger than 

 the wife, boys and girls will be produced in equal number. If both parents are 

 of the same age, there will 1029 boys and 1000 girls; if the husband is older, as many 

 as 1057 boys to 1000 girls. The general application of this law is contested by 

 some. Nutrition, further, appears to have some influence. Fetuses with ad- 

 herent placentas that communicate through the fetal vessels are always of the 

 same sex. Acardiac twins that receive blood that has already nourished the 

 normal twin are always of the same sex as the well-developed twin. These 

 facts find explanation in the remarkable observations upon armadillos. In 

 these mammals, the numerous young of the same brood, all of which develop 

 normally within the same chorion, are always of the same sex. In insects the 

 nutrition plays an important role, the best-nourished brood forming females in 

 preponderant degree. In man, impaired nutrition of the mother leads to the 

 expectation of male children. It has, further, been maintained that more male 

 progeny result when greater demands are made upon the father, also when im- 

 pregnation of the wife occurs late, and finally when the father is very young 

 or very old (when the father has reached middle age, more girls are born). Ac- 

 cording to Diising, in general the impregnation of a young ovum with an old 

 spermatozoid, when the mother is well nourished, more frequently results in female 

 progeny, and conversely the impregnation of an old ovum with a young sper- 

 matozoid, especially when the nutrition of the mother is somewhat impaired, more 

 frequently results in male children. Thury believed that animals (cows) that 

 are covered shortly after heat more frequently bear female offspring. Fiirst 

 believes the opposite is the rule for man. Fiquet maintained that female calves 

 can be produced if the cow is poorly nourished while the bull is well nourished 

 for weeks before intercourse. Other investigators have come to the conclusion that 

 the sex is unalterably established already at the time of conception. Also Pfliiger's 

 investigations have shown that all external influences (in frogs) during develop- 

 ment are without effect upon the development of the sex, that the latter, there- 

 fore, is definitely established before impregnation. Hermaphrodites are common 

 among tadpoles, later becoming males or females. 



