18. Q. What are orders? A. They are groups of the same class related by a
common structure.
19. Q. What is a family or genus? A. A still smaller group having
generally the same essential structure.
20. Q. What is a species? A. It is the smallest group whose structure is
constant.
21. Q. What are individuals? A. They are the units of organic life,
forming a complete animated existence.