Bilateral symmetry in chick embryo determination by gravity.

The determination of bilateral symmetry of chick blastodiscs occurring during the second half of the uterine period is only indirectly caused by the intrauterine rotation of the egg. As a result of this rotation the blastodisc is forced into an oblique position and the force of gravity affects the symmetrization process. The same result may be artificially achieved, without rotation, by forcing the blastodisc into an oblique position.