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Strains of Colpoda maupnsi previously reported were found to produce only octogenic reproductive cysts and monogenic wrinkled resting cysts. The present form of C. niaupasi (Bensonhurst strain), isolated by the senior author in 1949, was found to produce, in addition t o the above, quadrigenic reproductive cysts, digenic corrugated (wrinkled) resting cysts, and smooth thick-walled monogenic, digenic and quadrigenic resting cysts. Some of the factors leading to the development of these cysts in the Bensonhurst strain are believed t o be related to nutrition, age and size of the trophic forms. The cytological changes in encystment and excystment were followed with particular attention to aging monogenic resting cysts. The latter were observed for over 4 years. TAGES IN T H E life cycle of Colpoda maupasihave been reported by other investigators ( 1,2,13). It has been shown that the present form (Bensonhurst strain) differs from those previously reported by the development of both quadrigenic and octogenic reproductive cysts and by the production of wrinkled digenic as well as smooth thick-walled resting cysts( 7-9).The purpose of this paper is to describe the morphological and cytological features of the various stages in the life cycle of the present strain as a basis for further esperimental studies on the influence of various physical and chemical factors. AIATERIALS AND METHODSA pure line culture of Colpoda maupnsi was started with a single corrugated (wrinkled) cyst isolated from an infusion of hay made in 1949. This individual was escysted in a sterile hay infusion to which was added a suspension of mixed bacteria obtained from the original culture. Resting cysts were isolated from this medium and disinfected for three minutes in a solution consisting of equal parts of 0.5% (w/v) phenol and 1 % (w /v) alkyl-aryl sulphonate (wetting agent). ?ifter five washings in sterile distilled water, the strain was established and maintained a t room temperature (26°C.) in distilled water to which a suspension of 48-hour-old culture of Serratia marcescens was added. The cycle described in this paper occurs in this type of maintenance medium. Mass cultures (500 ml.) were grown in this medium in surgical dressing jars with modified covers, and sterile slides for attachment of the ciliates were suspended in the fluid by special holders. For excystment the following fluids were used: hay tea, bacterial suspensions in distilled water and Osterhout's solution.Cysts and trophic individuals were collected as they adhered to slides. They were fixed in Schaudinn's fixative or in alcohol-formalin mixture, or were heatkilled. Centrifuge concentrates of protozoa were also fixed in hot Schaudinn's on albumin-coated slides. Freeswimming forms were stained with iron-alum hema-toxylin, by the Feulgen technique and Corliss' modification of the Chatton-Lwoff method ( 4 ) . The Feulgen stain was found to penetrate the cysts and was used as the best means of studying nuclear cytology rather than of determining relative amounts of desoxypentos...

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