The thickend rim of the blastoderm evident during late blastula and gastrula stages[FishBase]. Embryonic structure which is a uniform thickened annulus at the blastoderm margin, consisting of two layers in addition to the EVL, the epiblast and the hypoblast. The germ ring is formed by the involution of the blastoderm back upon itself[ZFA] [ http://www.fishbase.org/glossary/Glossary.php?q=germ%20ring ]
TODO - check timing of appearance and disappearance - check relationship with primitive streak. he blastopore lips in amphibians appear to have the equivalent function of the germ ring in zebrafish (ES)
Embryonic structure that forms as a thickened annulus at the blastoderm rim. The germ ring is thickened because it is the involuting margin of the blastoderm[ZFIN:ZDB-PUB-961014-576].