Sentence:  Thus, if some old rhyme or saying has in one place a solemn import in philosophy or religion, while elsewhere it lies at the level of the nursery, there is some ground for treating the serious version as the more original, and the playful one as its mere lingering <WSD>survival</WSD>. 
Meaning of the word marked with <WSD> tags:  A custom or belief that persists in folklore from earlier times, when the rationale behind it is forgotten.