THE HORMONES IN HUMAN REPRODUCTION 



action. Such a mechanism is common in the body. That is how 

 food is shoved along in the intestines. That is how a horse 

 gets water through his esophagus up to his stomach when 

 his mouth is away down in the pond. Similar contractions of 

 the walls of the ureter force urine from kidneys to bladder, 

 no matter what position the body may be in with respect to 

 gravity. We know that the muscular walls of the oviducts 

 undergo contractions which could move the eggs, and we 

 know also that these contractions are under the influence of 

 the hormones of the ovary, changing their rhythm and inten- 

 sity at the very time the eggs are in transport. Burdick, 

 Pincus, and Whitney have been able to lock the ova in the 

 oviducts by administration of an ovarian hormone. Most stu- 

 dents of this problem now think, therefore, that the chief 

 method of transport of the eggs is by rhythmic contractions 

 of the tubal muscles, and that the cilia play at most only a 

 secondary role. 



I have long thought that we ought not to emphasize the 

 oviduct solely as an organ for transporting the ova, but 

 rather as a means of delaying their transportation. We are 

 going to see (in Chapter V) that the mammalian embryo, 

 reaching the uterus naked, delicate, and yolkless on the fourth 

 day after leaving the ovary, requires immediate nourishment 

 and a soft succulent place in which to grow. The uterus must 

 have time to get ready for its exigent tenant. If the embryos 

 arrive too early they cannot develop. I believe that one of the 

 most important functions of the oviduct is to hold back the 

 eggs until the uterus is ready for them. 



The uterus. When the eggs pass from the oviduct into the 

 uterus they find themselves in a chamber of larger size, with 

 heavier and more muscular walls. 



The uterus is built on fundamentally the same plan in all 

 mammals, although its form varies a great deal in different 

 species. It consists basically of two tubular canals, one right 

 and one left, corresponding to the two ovaries and oviducts. 



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