apologue vs novella

apologue

noun
  • A short story with a moral, often involving talking animals or objects; a fable. 

  • The use of fable to persuade the audience. 

novella

noun
  • A short novel or long short story. 

  • Synonym of novel (“new legal constitution in Ancient Rome”) 

How often have the words apologue and novella occurred in a corpus of books? (source: Google Ngram Viewer )