Filter linked cells from alone cells

[Paul AVILLACH]

Dear ImageJ Community,
Sorry for this new-bye question.
On a image I have 2 types of cells grouped cells attached together  
and alone cells.
Does anyone know how to filter grouped cells from alone cells?
After a Threshold of my image the quality is not good enough to keep  
all the link between the cells so I get a lot of wrong isolated cells  
after a Analyse particle setting a min and max.

Any clue?

Thanks a lot

Paul A