The Fetal Membranes 



61 



is the greatest occurring at any epoch in life. The death is 

 unseen, and is necessarily designated sterility. The newly 

 created individual needs greater fixidity in its place, more 

 accurate protection against invasion, and especially a safe 

 and abundant food supply. While the ovum lies free in the 

 uterine cavity, any liquid nutriment available is in constant 

 danger of being contaminated by any bacteria or other dele- 

 terious substances present in the uterus. Such toxic sub- 



Fig. 29— Maternal (bottom) and Fetal (top) Cotyledons of Cow 

 partly detached. A portion of the uterine wall seen 

 at bottom and of choriom at top. 



stances constitute a menace by threatening to invade the 

 new individual mixed with nutritive substances, through a 

 common portal, the external layer of the morula. The nu- 

 trition needs to be more dependable, abundant, and imme- 

 diate, and guarded as far as possible against contamination 

 from every source. The uterine seal hermetically closes the 

 cervical canal to direct invasion from the vagina. Since 

 the ovarian end of the genital tube, though opening into the 



