Diagrammatic projection of the vascular system of the yolk sac of a somewhat older embryo.
Superficial to it is the amnion, and below it is the yolk sac.
The external gills are moderately long, slender, and filamentous; the yolk sac is still moderately large.
The external gills are long and filamentous, and the yolk sac is large.
The yolk sac retracts mainly during hatching; it sometimes ruptures after hatching.
This point is where the communication exists between the inside of the tube, which is the embryo, and the yolk sac.
yolk sac n.
A membranous sac attached to an embryo, enclosing food yolk. Also called umbilical vesicle.
|yolk sac |
A sac that is attached to the gut of an embryo and encloses the yolk in bony fish, sharks, reptiles, mammals, and birds. In most mammals, the yolk sac functions as part of the embryo's circulatory system before the placenta develops.