yolk sac

IPA: jˈoʊksˈæk

(anatomy) A membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals.

Examples of "yolk-sac" in Sentences

_Philozoon_ (far better than a yolk-sac) survive a fortnight or more in
This yolk-sac allows the alevin to attain a relatively large size in the first month or so of its life and eliminates the total dependence on feeding.
It was known by the 1860's that various nutritive, respiratory, and excretory organs (yolk-sac, allantois) characteristic of embryos are lacking in all adults.
When hatched out and kept in water containing a very large quantity of air in solution, I found that sometimes alevins developed an air bubble in the yolk-sac.
On developing this bubble they are unable to stay at the bottom as they usually do, but swim about on their backs at the surface, with part of the yolk-sac out of the water.
They are all of similar size, being 165 mm. in length, but had evidently not nearly reached their full foetal development, as the yolk-sac is large 66 mm. in diameter and almost globular.
In its ball-like form and short thick peduncle, the yolk-sac of Centrophorus agrees with Squalus, and differs greatly from that of Galeus, which I have described as of peculiar shape, provided with a long umbilical cord, entering the sac towards the larger end.