They could be whipped stitched together by hand or appliqued down with a zigzag on a piece of material. You would lose the see through quality if you did that, and I suspect you want a lace. If you made more of the sides, you could use the center ones as cutwork for a table cloth. You have a lot of ways you could go with these. They would really be neat on a vest as a bottom fringey type strip. Use the centers as cut outs to see through the vest material. Or on a really pretty shawl with part of the border as the lace and others as the solid fabric. So many ideas are rushing through my head....too many.
To keep it lacey and as a former crochet addict, I would probably try something with crochet thread, the really small stuff, like a slip stitch holding each block together. I hope you post another pic when you are done. Those are really amazing!