The video sequence at the right was kindly provided by Dr. M. Danilchik, Univ. of Oregon Health Sciences Center. It shows how germ plasm becomes asymmetrically distributed as a result of subcortical rotation movements of the fertilized Xenopus egg. The germ plasm is the brightly colored region of the vegetal cytoplasm that becomes segregated to specific blastomeres by the four-cell stage. The stain used here detects mitochondrial, which are found at much higher density in the germ plasms of many organisms, including worms, flies, and frogs.