THE HORMONES IN HUMAN REPRODUCTION 



workers, Karl Ernst von Baer solved the puzzle in 1827 by 

 finding that the actual egg is a very small speck inside the 

 follicle, too small to be picked out by the unaided eye. If we 

 take one out of its place in the ovary and put it by itself in 

 a dish of clear water in a bright light it can just barely be 

 seen. 



With modern instruments we can make a very thin slice of 

 an ovary, put it under the microscope, and photograph it. 

 Studying the slide from the surface down (Plate VII, B) we 

 see a layer of covering cells (germinal epithelium), appearing 

 as a dark line at the top of the photograph, with a vague 

 zone of connective tissue beneath it, a zone of egg cells in 

 reserve (c) and follicles (/) of various sizes, each containing 

 its egg. 



The follicle (see again Plate VII, ^) is lined with a layer 

 which looks granular under low magnification, because it is 

 made up of small cells. Just outside this granulosa layer is 

 a thin layer (called thee a interna) of larger cells well sup- 

 plied with blood vessels. This layer, so slight that it would 

 hardly be noticed, except by an experienced microscopist, is 

 of great importance because in all probability it is the source 

 of the estrogenic hormone which (next to the egg) is the most 

 important product of the ovary. 



How the eggs are formed in the ovary is an unsettled prob- 

 lem. We know that large numbers of them are produced by 

 ingrowth from the surface cells of the ovary before birth. In 

 a newborn baby girl there are already thousands of egg cells, 

 many more than she can possibly need when she grows up. 

 Many anatomists think that these original eggs, present at 

 birth, furnish the supply for life ; in other words, that no new 

 ones are formed after birth. This means that the infant in 

 arms has already set aside her contribution to the heredity 

 of her children, and if perchance she has her last baby at 

 forty years of age, that particular egg will have waited all 

 those forty years for its opportunity to develop. This is 



{ 34 ) 



