What does blastula mean?
The blastula is one of the earliest stages in the development of an animal embryo. After a fertilized egg undergoes rapid rounds of division called cleavage, it becomes a hollow sphere of cells known as the blastoderm, enclosing a fluid-filled interior called the blastocoel. This structure is the blastula. In many animals it forms quickly — in sea urchins within a day of fertilization — and marks the point at which the embryo consists of many cells but has not yet begun forming distinct tissue layers. The blastula's significance lies in what comes next: through the process of gastrulation, its cells rearrange and migrate inward to produce the layered gastrula, from which all the body's organs eventually develop. In mammals, the corresponding stage is called a blastocyst, which has specialized regions destined to become the embryo and placenta. The word derives from Greek blastos, meaning a bud or sprout, and belongs firmly to the vocabulary of embryology and developmental biology rather than general conversation.
nounAn early stage of an animal embryo following cleavage, consisting of a hollow sphere of cells (the blastoderm) surrounding a fluid-filled cavity called the blastocoel.
- The early embryonic stage in animals consisting of a hollow sphere of cells surrounding a fluid-filled cavity (the blastocoel), produced by repeated cell division of the fertilized egg.
"The fertilized egg divides rapidly, forming a blastula within the first few days of development."
"In sea urchins, the blastula forms within hours of fertilization as the embryo floats freely in seawater."
"During the blastula stage, the cells are still largely undifferentiated and have not yet committed to becoming any particular tissue."
The Latin-style plural 'blastulae' is preferred in formal scientific writing; 'blastulas' is an accepted anglicized alternative.
"The culture dish contained dozens of blastulae at varying stages of development."
Every animal that has ever existed — from jellyfish to humans — passed through a hollow ball of cells called a blastula on its way to being something more.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of blastula
The word 'blastula' comes from Greek 'blastos', meaning a bud, sprout, or germ, combined with the diminutive suffix '-ula' adopted through New Latin. It was coined in the nineteenth century as embryologists developed systematic terminology for the successive stages of early development. The same Greek root underlies a whole family of embryological terms, including blastocyst, blastoderm, blastocoel, and gastrula (via the related concept of the gaster, or belly), reflecting how deeply this root shaped the vocabulary of developmental biology.
How blastula is actually used
A technical term used almost exclusively in developmental biology, embryology, and related scientific contexts; it is rare in everyday speech. The plural 'blastulae' follows Latin conventions and is standard in scientific writing, though 'blastulas' also appears in less formal usage.
Easily confused with blastula
A blastocyst is the mammalian equivalent of the blastula, distinguished by an inner cell mass that will form the embryo proper and a trophoblast that will form part of the placenta.
The gastrula is the next stage after the blastula, formed when cells migrate inward during gastrulation to create layered tissue.