1. When the three species of free-living flagellates employed in this investigation are subjected to the high centrifugal force obtained by the use of the air-driven centrifuge, stratification of the cytoplasmic components and inclusions takes place.
2. This stratification is most noticeable in the chlorophyll bearing Euglena. The chloroplasts form a belt having on the centrifugal side paramylum and neutral-red bodies, while the clear cytoplasm containing small spherical bodies, probably mitochondria, is at the centripetal pole 3. This stratification is a temporary process. Complete redistribution of the parts can take place. The orientation of the stratification is not dependent on the morphological polarity of the organism. The heaviest components may occupy the anterior, posterior, or lateral part of the organism.
4. There is no evidence that the bodies which stain intra vitally with neutral red are homologous with the Golgi bodies of the metazoa. On the contrary there is some new evidence to support the findings of Baker (1933) that these bodies stainable with neutral red give a metachromatic reaction with Meyer's methylene-blue method, and are therefore probably identical with volutin. We have reached no satisfactory conclusion regarding what structures represent the Golgi apparatus. The theories put forward by other observers are briefly discussed.
5. Fixatives containing osmic acid show spherical bodies close to the periphery of the organism. They are not moved by the centrifugal force.
6. Short notes are given on the effect of the ultra-centrifuge on Menoidium sp. and on Chilomonas paramecium. As in Euglena the heaviest materials in Menoidium are the paramylum and bodies stainable with neutral red. In Chilomonas starch grains and neutral-red-stainable bodies are displaced to the centrifugal pole. In control specimens of Menoidium there is sometimes a natural stratification to be observed the paramylum and neutral-red bodies being gathered together usually at the anterior end of the organism.