The opening of Letter XXVIII
DEFINITION OF THE TERM INSECT.
What is an insect? This may seem a strange question after such copious details as have been given in my former Letters of their history and economy, in which it appears to have been taken for granted that you can answer this question. Yet in the scientific road which you are now about to enter, to be able to define these creatures technically is an important first step which calls for attention. You know already that a butterfly is an insect--that a fly, a beetle, a grasshopper, a bug, a bee, a louse, and flea, are insects--that a spider also and centipede go under that name; and this knowledge, which every child likewise possesses, was sufficient for comprehending the subjects upon which I have hitherto written. But now that we are about to take a nearer view of them--to investigate their anatomical and physiological characters more closely--these vague and popular ideas are insufficient. In common language, not only the tribes above mentioned, but most small animals--as worms, slugs, leeches, and many similar creatures, are known by the name of insects.