EXCRETION • FREE TRANSLATOR.ORG • Definition of Excretion

... the animal, and that to form the animal it sufficed to cover this foundation with a system of organs fitted to establish relations with the world outside. It follows that the functions of the animal form two quite distinct classes. One class consists in a continual succession of assimilation and excretion; through these functions the animal incessantly transforms into its own substance the molecules of surrounding bodies, later to reject these molecules when they have become heterogeneous to it. Through this first class of functions the animal exists only within ...

— Form and Function - A Contribution to the History of Animal Morphology • E. S. (Edward Stuart) Russell