Changes in shell membranes during the development of quail embryos

The shell membrane of an avian egg acts as a bag enclosing albumen and water. At its interface with the albumen, a smooth layer of homogeneous, dense material called the limiting membrane demarcates the shell membrane. The present study aimed to investigate changes in the limiting membrane during development of quail embryos that were grown with or without being turned. Sixty-three percent of the embryos were hatched after the eggs were incubated at 39 C and in 60% humidity with automatic rotation around their long axis and with their equatorial side down, whereas the hatch rate decreased to 24% when the eggs were incubated without being turned. The width of the limiting membrane at the equatorial region of turned eggs gradually decreased from 74 nm on Days 0 to 2 of incubation to 35 nm on Day 10 and thereafter. Conversely, water permeability, measured by evaporation through the shell membrane increased from 4 to 5 nL/mm2 per min on Days 0 to 6, to 9 nL/mm2 per min on Day 12 and thereafter. In stationary eggs, the decrease in the width of the limiting membrane on the lower side of eggs was delayed until Day 8 of incubation. The water permeability of the shell membrane in this group was 51% of that of the membrane on the upper side of eggs on Day 8 of incubation. Forty to forty-four nanometers seemed to be the critical width of the limiting membrane at which high water permeation could occur. It was also shown that the albumen hinders water permeation through the membrane. These results show that (1) the limiting membrane is made thin during the development over the whole surface with egg-turning, possibly through digestion of still unknown agents, and (2) this thinning accelerates the rate of water permeation through the membrane.