[Yolk sac development in two-humped camel embryogenesis].

The early formed yolk sac is observed in the embryo of Camelus bactrianus at the stage of 7 pairs of somites at the age of 22-24 days. The yolk placenta is formed at the stage of 17-22 pairs of somites at the age of 27-28 days. The yolk placenta of the Camelus bactrianus is functioning for a long time: during the embryonic and prefetal periods. Yolk hemopoiesis lasts from the middle of early embryonic period up to the second half of the late prefetal period. A continuous existance of the yolk sac in Tylopoda is likely to be a primitive feature of their development.