Nearly all eukaryotes have an exterior plasma membrane with glycoproteins on the outer leaflet however. The exception may be the intracellular microsporidian parasites which have an outer membrane with an exterior leaflet bearing only cytoplasmic proteins. How can this be? The initial stage, the sporoplasm, is injected into a host cell and its outer membrane appears to be derived from a cytoplasmic organelle referred to as the extrusion apparatus. The introduced microsporidian cell retains this organelle membrane with its outer leaflet of cytoplasmic proteins throughout the remainder of its life cycle. A conventional plasma membrane does appear but only during spore wall formation and this membrane remains interior to the microsporidian while it is engaged with the development of the external wall whereas, the outside cytoplasmic membrane remains exterior to the developing spore wall. The intracellular microsporidia, which locate within the host cytoplasm, has its external membrane leaflet in direct contact with the host cytoplasm. All the cytoplasmic proteins on this exterior membrane of the microsporidian are believed to be of host origin and, therefore it is not surprising that the parasitic cell does not yield a detectable reaction either by the host cell or the host organism. This study is based on observations on the microsporidians Spraguea amricanus, Anncaliia algerae, Ameson Michaelis, and Thelohania sp.