Ring Structure of Avian Egg Yolk

Differences in the staining properties of yolk deposited during night and day were used to estimate the time required to deposit yolk within the ovarian follicle. Whole eggs were frozen to −10° C. to alter the lipoproteins, the shell was removed, and contents fixed in 4% formalin for 18 hours at 60–70° C. The yolk was cut in half, and one half was put into 6% potassium dichromate for 18 hours at 60–70° C. Slices revealed alternating light and dark grey-green or brown rings. The center (latebra) was always light. From timed dye-feeding experiments it was found that lighter staining rings were deposited at night. Chicken eggs had 7–11 light rings; coturnix quail 4–6; turkeys 10–12; and cackling geese 12. All eggs from a variety of bird species showed ring structures. Staining formalin-fixed slices with acidified ferrocyanide yielded rings of Prussian blue, a test for forms of iron. Variation in the nutrition of the reproducing female, or the effects of acute contacts with environmental contaminants can be localized in discrete rings of yolks without experimental intervention during yolk deposition.