THE HORMONES IN HUMAN REPRODUCTION 



by filtration through these apposed membranes. When the 

 pigs are born the membranes ("afterbirth") simply peel off 

 the lining of the uterus leaving the latter more or less intact. 

 In most mammals, however, the contact becomes much more 

 intimate. The membranes send down long rootlike processes 



5 ImplantQllon of the Imman embryo 



Fio. 14. Diagrams showing implantation of the embryo, in the rabbit 

 and human. In the rabbit figures the uterus is represented as if cut trans- 

 versely, as one slices a banana; in the human figures the uterus is cut 

 lengthwise as one halves a pear. From Attaining Manhood, by George W. 

 Corner, by courtesy of Harper and Brothers. 



into the uterine lining or endometrium. This is illustrated in 

 the diagram of the rabbit's implantation (Fig. 14). In the 

 human and a few other animals, the early embryo settles down 

 not merely on the inner surface of the uterus, but actually 

 burrows down into the lining, and sends out its rootlike 



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