FIGURE 1.

Stages of chicken follicle development. A, the follicles of the first phase of development are 2–4 mm in diameter, lack bona fide yolk and the typical yellow color, and are thus named small white follicles. B, during the second developmental phase, follicles reach a diameter of 6–8 mm. The uptake of yolk precursors is initiated, and follicles start to become yellow. Follicles in this phase are called large white follicles (empty arrowheads) and small yellow follicles (black arrowheads). C, the third phase of follicle development is characterized by the uptake of large amounts of yolk precursors, accompanied by an increase in diameter from 8 to 35 mm. The biggest follicle that is the next to the ovulate is named F1. D, follicles in the transition from phase 2 to phase 3 represent the pool of follicles that will enter the final rapid growth phase and then ovulate within the next 7 days. Follicles are arranged according to size, from the smallest large white follicle (VI) to the biggest small yellow follicle (I). F6 represents the smallest follicle of the final rapid growth phase.