I wrote the first Edition of 1810 in a kind of inspiration, and on that account it was not so well arranged as a systematic work ought to be. Now, although this may appear to have been amended in the second and third edition, yet still it was not possible for me to completely attain the object held in view. The book has therefore remained essentially the same as regards its fundamental principles, such as those concerning the formation of matter, the protoplasmic substance (_Schleim-Substanz_) and vesicular form of the organic mass, the signification and function of the organs, as also the principles of classification in Minerals, Plants and Animals, so that all this is consequently as old as the first edition. It is only the empirical arrangement into series of plants and animals, that has been modified from time to time in accordance with the scientific elevation of their several departments, or just as discoveries and anatomical investigations have increased and rendered some other position of the objects a matter of necessity. This susceptibility to change will of course be persistent in the future, although the principles themselves should continue wholly unchanged; ay, the very stability of the latter will tend the more to invite the naturalist to the pursuit of empirical inquiries, by determining beforehand in what direction he is to extend his point of view, and thus spare himself the trouble of blindly and laboriously groping about in the dense labyrinth of facts. Such a work therefore as the present can only approximate completion through the progress made in science, and each new edition will supply some defect of its predecessor in the distribution or parcelling out of things.