Reorganization of the cortical layer during cytokinesis in mouse blastomeres

Mouse blastomeres in metaphase and in early and mid-cytokinesis were extracted with 50% glycerol, then deglycerinated and thin sectioned. A continuous layer of microfilaments was found in association with the plasma membrane. A loose network constitutes this layer during metaphase, whereas in early cytokinesis filaments tend to be packed more tightly and oriented parallel to the long axis of the cell. During mid-cytokinesis this arrangement is similar, except in the contractile ring which consists mainly of circumferentially arranged filaments.