Avian Spare Yolk and Its Assimilation

Abstract

IT is well known that at the time of hatching a bird still retains a portion of unassimilatcd yolk material. About two days before the embryo is ready to bc hatched, a rapid growth and unfolding of the tissues at the umbilicus cause that portion of the yolk which has as yet not bccn absorbed to bc enclosed within the abdominal cavity. After enclosure of the yolk, its utilization goes on as before until, under normal conditions, it has bccn entirely absorbed. Since the yolk sac is actually a divcrticulum of the small intestine, its material is absorbed directly from the sac into the blood stream. The spare yolk, in this manner, is able to supply the developing chick with a store of nutriment which enables it to survive for a limited period after hatching without an additional supply of food.