The Collaborative International Dictionary of English v.0.48:

blastocoel \blastocoel\, Blastocoele \Blas"to*c[oe]le\
blastocoele \blastocoele\, n. [Gr. blasto`s sprout + koi^los
   hollow.] (Biol.)
   The cavity inside a blastula; -- also called segmentation
   cavity.
   [1913 Webster]

WordNet (r) 3.0 (2006):

blastocoele
    n 1: the fluid-filled cavity inside a blastula [syn:
         blastocoel, blastocoele, blastocele, segmentation
         cavity, cleavage cavity]