blas·tu·la 
(blăschə-lə)
(blăschə-lə)n. pl. blas·tu·las or blas·tu·lae (-lē′)
An early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity. Also called blastosphere.
[New Latin : from Greek blastos, bud + Latin -ula, feminine diminutive suff.]
blastu·lar adj.
blas′tu·lation (-lāshən) n.