What structure forms in prophase along which the chromosomes move?

Microtubules forms in prophase along which chromosomes move.

Explanation:

Prophase is the first phase of mitotic cell division. It is the longest phase of the cell division. This is the starting phase of karyokinesis. The nuclear membrane and nucleolus disappears.  

The chromosomes are uncoiled and separated from each other . But it is attached with the centromere. Thus the number of chromosomes become double.  

Two centrioles are start separating towards the pole. They form elongated microtubules, which gets attach with the centromere of the chromosome. Then the centrioles are located at 2 poles.  

The microtubules on further stages pull the chromosomes to separate and helps them to locate at two poles. Thus 2 daughter cells will form.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.