THE EGG 



teed to degenerate while in the oviduct. Others degenerate in 

 the ovary, sometimes even before well-developed follicles have 

 formed about them, sometimes in large follicles. When this 

 happens, the follicle also ultimately degenerates and disap- 

 pears from the ovary. Such follicles are shown in Plate VII, 

 A, B. 



A Swedish investigator, Haggstrom, who counted the eggs 

 in both ovaries of a 22-year-old woman, found about 420,000. 

 Yet a woman who sheds one egg per month without interrup- 

 tion by pregnancy or illness during her entire life, from say 

 the 12th to the 48th year, cannot use up more than 430-odd 

 eggs. The most prolific egg producer among mammals, the 

 sow, might possibly shed a total of 3,000 to 3,500 eggs, allow- 

 ing ten years of ovarian activity not interrupted by preg- 

 nancy, and assuming the very high average of 20 eggs at 

 each 3-weekly cycle ; but she has vastly more than this in the 

 ovaries at birth. Whether or not there is new formation of 

 eggs during adult life (as we discussed above), there is evi- 

 dently a large overproduction of eggs in the ovaries. This, 

 and a corresponding but enormously greater overproduction 

 of sperm cells, is thought to be a survival from earlier evolu- 

 tionary stages when germ cells were discharged into the water 

 to take the risk of enemies and mischance. 



When the reproductive period of life is over, there are still 

 many eggs in the ovaries. These gradually diminish in number, 

 but some of them may persist to advanced ages. 



The corpus luteum. When the eggs of a frog or fish are 

 spawned into the water the ovary has done its work. There is 

 nothing more it can do for the eggs. It shrinks back to the 

 insignificant bulk it had before the eggs began to ripen and 

 nothing more is heard from it until the next breeding season. 

 Not so in the mammals. Their eggs are not thrust into the 

 outside world. The mother is still intimately responsible for 

 them; they must be nourished and sheltered within her for 

 weeks or months to come. The uterus is to be altered to receive 



i 41 ) 



