Cellular changes in the granulosa layer of the maturing ovarian follicle of the domestic fowl.

1. The relationships between length, width and height of the maturing ovarian follicle of the domestic fowl (Gallus domesticus) are shown. 2. During the rapid-growth phase (yolk deposition) of the oocyte, i.e. an increase in size from about 9 mm diameter to 35 mm diameter, there is about a 15-fold increase in its surface area. During this time the number of granulosa cells adjacent to the oocyte increases by about 5-fold. 3. The granulosa cells become flatter during the growth period of the follicle, consequently increasing their surface area adjacent to the oocyte by about 3-fold. 4. Together the change in shape of the granulosa cells and the increase in their number account for the increase in area of the granulosa layer during follicular growth. 5. Measurement of the DNA content of the granulosa layer indicated a progressive decrease in the cellular content of DNA as the follicle matures.