blastosphere

When the egg of Amphioxus is in the blastosphere stage we cannot speak of either an epiblast or hypoblast.

The hollow sphere which is thus formed is the important stage of the “germinal vesicle,” the blastula, or blastosphere.

Thus, an oval and an elongate egg produce respectively an oval and an elongate blastosphere.

A limit is set to increase in the size of a blastosphere by the nature of the material of its walls.

The central part of the blastosphere is called the segmentation cavity or blastocoel.