Formation of the Cyst Wall of the Ciliate Colpoda steinii

After a thin membranous envelope surrounding the cell body and cilia of Colpoda steinii has been formed, the main mass of the proteinaceous cyst wall is deposited without exocytosis. It can be composed of two layers, the denser and wrinkled ectocyst and the smooth-walled endocyst; however, the ectocyst may be missing. Evidence is presented that ecto- and endocyst are formed from vesicles derived from abundant rough endoplasmic reticulum which appears at the time of wall formation. The cilia are retained and become embedded in the peripheral cytoplasm. Synthesis of RNA and protein is required as actinomycin C and cycloheximide block cyst formation. Calcium is required during a sensitive phase prior to encystment.