parablast

noun

1. A portion of the mesoblast (of peripheral origin) of the developing embryo, whose cells are involved in the formation of the first blood and blood vessels.

   “The study of the relations of the' wall in the chick induced him to think that the elements of the white yolk he came parablast cells; moreover, the study of the hen's ovary led him to the conclusion that the white yolk was developed from the granulosa cells, and that these cells arise from leucocytes.”