CYTOPLASMIC MICROTUBULES IN DIFFERENT ANIMAL CELLS.

In avian, murine, and human cells fixed with glutaraldehyde, cytoplasmic microtubules 180 to 250 A in diameter and of undetermined length were found. These cytoplasmic microtubules are similar to those described by Ledbetter and Porter in plant cells after the same glutaraldehyde fixation. The cytoplasmic microtubules in animal cells are connected with the satellites of the centrioles and are similar to the mitotic spindle fibers. Their protein nature and their possible role in maintaining the shape of the cells are discussed. Their presence in all examined animal cells as well as in plant cells favors the hypothesis that they are a permanent component of the cytoplasm.