(a) In interphase animal cells, the (−) ends of most microtubules are proximal to the MTOC. Similarly, the microtubules in flagella and cilia have their (−) ends continuous with the basal body, which acts as the MTOC in these structures. (b) As cells enter mitosis, the microtubule network rearranges, forming a mitotic spindle. The (−) ends of all spindle microtubules point toward one of the two MTOCs, or poles, as they are called in mitotic cells. (c) In nerve cells, the (−) ends of axonal microtubules are oriented toward the base of the axon. However, dendritic microtubules have mixed polarities. (d) In plant cells, which contain numerous MTOCs, microtubules line the cell cortex. Webs of microtubules cap the growing ends of a plant cell.