Label the diagram and also determine the stage at which this structure is visible.

(N/A) The provided diagram illustrates the transition phase from prophase to metaphase during mitosis.
In the transition phase,the chromosomes are seen moving towards the equatorial plane,guided by the spindle fibres attached to the kinetochores.
The key structures labeled are:
$1$. Dividing centriole: These move to opposite poles to form the spindle apparatus.
$2$. Spindle fibre: Microtubules that attach to the kinetochores of chromosomes.
$3$. Chromosomes on the equatorial plane: This represents the final alignment stage of metaphase.
$4$. Chromosomes moving towards the equatorial plane: This is the characteristic feature of the transition from prophase to metaphase.