Sentence:  Here Apollo killed a serpent called the <WSD>Python</WSD>, and established a great prophetic shrine. Sometimes it is said that the Titaness Themis had the shrine before him, and this, as well as the killing of the <WSD>Python</WSD>, suggests that Apollo took over a place already of religious significance, associated with chthonic (i.e., earth) powers. 
Meaning of the word marked with <WSD> tags:  The earth-dragon of Delphi, represented as a serpent, killed by Apollo.