The Reproductive Organs 335 



At the anterior end, this infiindibiilum grows forward beneath 

 the WolfBan body and dilates to form a sac which is to constitute 

 the pelvis of the kidney, while, from its walls, a number of 

 branching tubules grow out to constitute the uninary tubules 

 and, at their ends, they enlarge to constitute the glomeruli of 

 the kidney. 



At the point of communication between the ureter and the 

 allantois the latter tube becomes dilated to constitute the urinary 

 bladder. Behind, the allantois is constricted to constitute the 

 urethra, while, in front, the narrowed portion which passes out 

 through the umbilicus is known as the urachus. During the 

 life of the fetus, the urine chiefly passes through the urachus, 

 which opening normally closes at the time of birth. 



The Reproductive Organs. 



The development of the reproductive organs of the female has 

 already been described on page 1 1 , to which the reader is re- 

 ferred. They undergo many aberrations in their development, 

 due to arrests, some of which have already been noted on page 

 247. Fig. 51 on page 323 illustrates an interesting form of 

 arrested development of the uterus and vagina, in which these 

 organs are represented by enlarged, solid cords. 



The Male Reproductive Organs. 

 The Testicles. 



The testes form, like the ovaries, in the genital ridges and in 

 the earliest stages the mode of origin or development can not be 

 differentiated in the two sexes. Later the differentiation occurs 

 through the development of some parts of the undifferentiated 

 genital gland and the atrophy of others. The Wolffian bodies 

 and ducts play an important part in the development of the ex- 

 cretory apparatus of the testicles. In the indifferent gland the 

 mesoblastic cells become grouped in cords containing small 

 cells, along with the larger and more numerous primitive 

 sexual cells. These .sexual cords are formed from the roundish 

 masses of cells, separated from each other by connective tissue 

 sheaths. They eventually become elongated and hollowed out to 

 constitute the seminiferous tubules. 



From the Wolfi&an bodies, cell cords grow out and fuse with 

 the semeniferous tubules to constitute the vasa recta and rete 



