Cytoplasmic streaming in a heliozoan

A method is described utilizing deuterium oxide stabilization of microtubules that allows the separation of stable axopodia from the cell body. In some instances the isolated axopodia are broken open and display two classes of cytoplasmic linear elements, microtubules and microfilaments, lying side by side. This morphological arrangement is consistent with the hypothesis that microtubules support a microfilament-based contractile apparatus in heliozoans and probably other cell types as well. Also included is a description of pseudopodial formation from axopodial cytoplasm in response to mechanical stimulation. The pseudopodial motility is discussed in relation to the particle saltations also observed in these cells and to different levels of organization or activation of the contractile machinery.