Explanation

There are 558 Rukus as a whole in the Holy Quran.

Ruku comes from an Arabic word رُكوع.

It is some part or paragraph in the Quran.

During the revelation of the Holy Quran, it was not sub-divided by Rukus.

 Rukuas were not there in the reign of Prophet Muhammad (SAW) and Sahaaba (R.A). 

These subdivisions were created during the reign of Hajaaj bin Yusuf.

The number of Ruku in the last chapter of Quran are thirty nine