Comparison of Skeletons of Red-Blooded Animals
Cuvier’s last words were supposedly “Nurse, it was I who discovered leeches have red blood.”
Linnaeus’s classification of species was highly dependent upon blood color and whether or not they were cold-blooded. Mammals, birds, amphibians [he included reptiles with amphibians], and fish all had red blood. Insects and “Vermes” (mollusks & related species) had white blood and no vertebrae.
Cuvier discovered that leeches had red blood early in his career, and this influenced his belief that Linnaeus’s system was far too simplistic, and that it was important to NOT focus on each group/species individually.
He believed that investigating the differences and similarities between groups and species was far more important than isolating everything in neat little capsules. Everything was related to everything else in some way. This was against everything that the prominent naturalists of the time believed, but eventually influenced a young Charles Darwin…what a cool guy.
Elementaire de l’Histoire Naturelle des Animaux par G. Cuvier, de l’Institut National de France. 1798.