Progressive disassembly of the mitotic spindle into two halves at anaphase and assembly of an astral neo-spindle during cleavage mitosis in the newt embryo.

In the second cleavage mitosis of newt embryos at anaphase, disassembly of mitotic spindle fibres, mediated by the 'plus' ends of their microtubules, results in equatorial division into two half-spindles. Yolk-filled cytoplasm invades the area free of fibres and is itself penetrated by antiparallel fibres from asters, which have become nucleated at opposite poles. These fibres immediately supplant the mitotic spindle; they participate in the lengthening of the interpolar distance and in the positioning of the newly formed daughter nuclei. The mechanisms of these successive phenomena must be considered in order to understand the complexities of the cell cycle in early mitosis.