Membranes are highly dynamic and operate not only as inert boundaries, but the packages they carry around in a cell are well addressed fro appropriate delivery. This holds for a variety of endomembrane systems engaged in exo- and endocytosis, for organelles along the biosynthetic pathway, phagosomes, and lysosomes. It also holds for the establishment of functional surface properties. Cell pairing (conjugation) phenomena are a good model for the problem of how a cell can discriminate between -self- and -non-self-. On the other hand parasitic sporozoa developed to experts in masking their...