invertebrate vs yellow back

invertebrate

noun

  • A spineless person; a coward. 

  • An animal without vertebrae, i.e. backbone. 

adj

  • Cowardly, uncourageous; lacking character. 

  • Lacking a backbone; without vertebrae. 

yellow back

noun

  • A coward. 

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