Membrane filters do not prevent cell contacts.
D000818:Animals; D002465:Cell Movement; D002469:Cell Separation; D002642:Chick Embryo; D004475:Ectoderm / Q000648:ultrastructure*; D004707:Endoderm / Q000648:ultrastructure*; D008851:Micropore Filters; D008854:Microscopy, Electron; D009420:Nervous System / Q000196:embryology*