The blobs are secretions coming out of the apex (=top) of the cells. Notice the cytoplasm of the cell (b).

Decrease the magnification. Only the apical part (d) of the ABO cells is shown here.
It seems that these ABO cells accumulate their secretions (whatever they are) beneath their apical membrane. Then the apex of the cells pinches off and the secretions enclosed in the plasma membrane (which looks like a blob). are released on the outside.

On the SEM photomicrograph, you can see different stages of secretion:
- accumulation of the products of secretion under the apical membrane (=formation of the blob) (3)
- release of the secretions (blob disappears)(A,B,C).