202 EMBRYOLOGY. 



organs seems to be that of temporary kidne} T s, but by the end of 

 the third month they have been replaced by the permanent organs, 

 and have almost entirely disappeared. 



How do the testicle and ovary originate ? 



The body (germinal epithelium) which appears on the inner side 

 of the Wolffian body is the nucleus of the future testicle or ovary, 

 while from the outer side there springs a duct (Miiller's) which 

 passes down to the cloaca or lower end of the hind-gut. At first it 

 is impossible to determine the sex of the fcetus. 



How do the remaining genital organs of the female develop? 



The ducts of Miiller join to form the uterus and vagina, while 

 the ununited portions remain as the Fallopian tubes. The Wolffian 

 ducts, which also spring from the Wolffian bodies, are rudimentary 

 in the female and appear as a part of the parovarium. 



How do the remaining male organs of generation develop ? 



The Wolffian ducts become convoluted tubules, and each is at- 

 tached to the testis as the epididymis. Miiller's duct is rudimentary 

 in the male, and is only found as the sinus pocularis and the hy- 

 datids of Morgagni. 



How are the external genitals formed? 



In both sexes in early fretal life the external genitals are alike, 

 consisting of a body resembling a penis with a fold of skin at 

 either side. In the female this body becomes proportionately 

 smaller, and appears as the clitoris, the two lateral masses becom- 

 ing the labia majora. In the male a groove on the under surface 

 unites at its borders to form the urethra, while the scrotum is formed 

 from the folds of skin at the side. This differen dated condition may 

 persist in adult life, and has been mistaken for hermaphroditism. 



PARTURITION. 

 How is the foetus extruded from the uterus? 



In part by the contraction of the uterine muscles, and in part by 

 the pressure exerted by the abdominal walls. The uterine contrac- 

 tions are the first to appear, and it is not until the foetus enters the 

 vagina that the abdominal muscles are brought into play. 



What causes excite the uterine contractions? 



As to this no satisfactory answer has been given. Why the 



