Each one of the follicles belonging to the latter group is identified
by a decreasing digit according to its size (i.e. the second largest
follicle is called F2, the largest follicle F1, etc.). Once a follicle enters
the hierarchical follicle category it cannot suffer atresia (Gilbert
et al., 1983; Johnson, 1996), and every day the largest follicle is
ovulated, while a new follicle is recruited to enter the hierarchy,
from a pool of 10 to 15 follicles that are 6 to 8 mm in diameter