A direct approach to the study of the effect of gravity on axis formation in birds.

A system has been developed to enable the normal development of aborted very early uterine avian embryos, outside the female's uterus. The shell-less aborted egg was put into a foster shell of a sister egg, previously laid by the same female. The empty space between the shell and aborted egg was filled with artificial uterine fluid. The reconstructed eggs were incubated at 42 degrees C for 30 hours in a vertical position. The atmosphere contained a high concentration of CO2 (8-10%). At the termination of the 30 h the eggs were transferred to incubation at 37 degrees C in normal atmospheric conditions. Normal development has been recorded for a certain percentage of eggs incubated up to 12 days. In other cases abnormalities, arrested development or development of extraembryonic membranes only, without a sign of an embryonic axis, have been observed. The three important conclusions from the above experiments were: 1. It is possible to develop a closed, self-contained system, disconnected from the female's body, that would support the development of early uterine embryos. 2. The incidence of embryo-less extraembryonic membranes in such a system, is correlated with the degree of detachment of the "yolk" from the outer envelopes. 3. Such a system can be further developed into an experiment suited for microgravity conditions which will be an alternative to an experiment with live birds. The experiment will be aimed at testing the importance of gravity in changing the radially symmetrical avian blastoderm into a bilaterally symmetrical blastoderm.