blastodisc

{{Short description|Embryo forming part of yolk}}

File:Cleavage.png undergoing cleavage]]

The blastodisc, also called the germinal disc, is the embryo-forming part on the yolk of the egg of an animal that undergoes discoidal meroblastic cleavage.{{cite web |title=Definition of BLASTODISC |url=https://www.merriam-webster.com/dictionary/blastodisc |website=www.merriam-webster.com |access-date=15 October 2022 |language=en}} Discoidal cleavage occurs in those animals with a large proportion of yolk in their eggs, and include insects, fish, reptiles and birds.{{cite book |last1=Gilbert |first1=Scott F. |title=Developmental biology |date=2006 |publisher=Sinauer Associates Publishers |location=Sunderland, Mass. |isbn=9780878932504 |page=215 |edition=8th}} The blastodisc is a small disc of cytoplasm that sits on top of the yolk. In birds, it is a small, circular, white spot (approximately 1.5-3 mm across) on the surface of the yellow yolk of an egg, at the animal pole.{{cite book |last1=Gilbert |first1=Scott F. |title=Developmental biology |date=2006 |publisher=Sinauer Associates Publishers |location=Sunderland, Mass. |isbn=9780878932504 |pages=336–337 |edition=8th}}