The mechanism responsible for final cell separation at the end of cytokinesis is currently unknown. Knockout strains of the ciliate, Tetrahymena thermophila lacking the kinesin-II homologous molecular motors, Kin1p and Kin2p are paralyzed due to their complete loss of cilia and undergo frequent cytokinesis failures. Observations of live dividing cells revealed that cleavage furrow ingression is normal in kinesin-II double knockout cells until the final stage of cell separation (Brown et al., 1999). During closer inspection of dividing cells using video differential interference contrast microscopy, we found that wild-type cells undergo an extremely complex motile behavior near the end of cytokinesis. This process, which we have named rotokinesis, appears to facilitate the physical separation of daughter cells. Here we present recent work on Tetrahymena rotokinesis, and review studies in other organisms which suggest that the use of cell locomotion in the completion of cytokinesis is a general phenomenon of motile cell types.

This article surveys several lines of evidence that suggest a strong connection among the mechanisms of color vision, perceptually elementary hues, and naming basic colors. But important questions remain about the linkage between the shared human attributes of color perception and the development and structure of crosscultural basic color categories.

Many realists have maintained that the success of scientific theories can be explained only if they may be regarded as approximately true. Laurens Laudan has in turn contended that a necessary condition for a theory's being approximately true is that its central terms refer, and since many successful theories of the past have employed central terms which we now understand to be non-referential, realism cannot explain their success. The present paper argues that a realist can adopt a view of reference according to which a theory might plausibly be said to be approximately true even though its central terms do not refer, or alternatively, he may construe reference in such a way as to assign reference to a range of successful older theories which includes Laudan's purported counterexamples.

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