Because of peeping through Siva - Parvati's bedroom, angered Siva deposits His Seeds (Rudra Veeriyam) on Agni Deva

Because of peeping through Siva - Parvati's bedroom, angered Siva deposits His Seeds (Rudra Veeriyam) on Agni Deva. To get rid of the heat Agni Deva takes bath in Ganges. The holy river Ganga carried the fetuses to a secluded place, called the Sara Vana, which was covered with reeds. The six 'Dvakannikas' (six women who represented the Pleiades or the Kritikas) who are taking bath in the Ganges became pregnant(Agni Devudu Rudraveeriyam / Ganga Madavil Rudraveeriyam).