The Collaborative International Dictionary of English v.0.48:

Periblast \Per"i*blast\, a. [Gr. periblasta`nein to grow around.
   See Peri-, and -blast.] (Biol.)
   The protoplasmic matter which surrounds the entoblast, or
   cell nucleus, and undergoes segmentation. --
   Per`i*blas"tic, a.
   [1913 Webster]