Abstract
Dynamic aspects of the cellular organization in a large amoeboid cell are discussed based on the following new findings in the plasmodium of the true slime mold. Upon stimulation, a large plasmodium breaks temporarily into pieces, each containing either about 8 or 4 nuclei. The rhythmic streaming of the protoplasm emerges only when the plasmodial size is larger than the critical value. This bifurcation among dynamic states is compared to that in the feeding behavior by a placozoan, the most primitive multi-cellular organism.