Into which two main groups did Aristotle divide animals?

Correct answer: Animals with red blood and animals without red blood

Correct answer: B. Aristotle divided animals into Enaima, or animals with red blood, and Anaima, or animals without red blood, according to the terminology commonly used in school biology. This was an early, simple classification based on an observable feature. A is incorrect because vertebrate and invertebrate grouping is a later and more formal classification based on the presence or absence of a vertebral column. C is incorrect because habitat was not the two-part division asked for in Aristotle’s scheme. D is incorrect because ability to fly also does not represent his principal two-group division. Be careful: “animals without red blood” does not mean that every such animal literally has no blood or no circulatory fluid; it describes Aristotle’s old observational category. Memory cue: Aristotle’s animal division = red blood versus no red blood, not backbone versus no backbone.