What is the shelled thing in the upper left? It seems to be formed of concentric spheroids.
It appears that the concentration of dye is very high around this location: everything is over stained. Because of the fact, almost a whole organelle happened to be explicitly revealed as concentric circles (we don’t know if they are spheroids because it’s just 2D ;). I assume, “endoplasmic reticulum” can be what we are looking at. and the dark region inside of the “7” shaped object at lower right side of it, seems to be the mitochondria.