I kept a few of these Cottony Cushion Scales in a jar.
These nympths emerged within a few days.
The egg sack just ruptures.
The second image the nympths are emerging from the egg sack.
As far as I can tell the sack is much like a spider sack with no internal organs of the adult inside.
Adult with egg sack 7-8-mm long >>

Nympths emerging >>