mere inventions, if they are not an attempt to classify for our own convenience the objects we study, then they are thoughts which, whether we detect them or not, are expressed in Nature,—­then Nature is the work of thought, the production of intelligence carried out according to plan, therefore premeditated,—­and in our study of natural objects we are approaching the thoughts of the Creator, reading His conceptions, interpreting a system that is His and not ours.

All the divergence from the simplicity and grandeur of this division of the animal kingdom arises from an inability to distinguish between a plan and the execution, of a plan.  We allow the details to shut out the plan itself, which exists quite independent of special forms.  I hope we shall find a meaning in all these plans that will prove them to be the parts of one great conception and the work of one Mind.

II.

Proceeding upon the view that there is a close analogy between the way in which every individual student penetrates into Nature and the progress of science as a whole in the history of humanity, I continue my sketch of the successive steps that have led to our present state of knowledge.  I began with Aristotle, and showed that this great philosopher, though he prepared a digest of all the knowledge belonging to his time, yet did not feel the necessity of any system or of any scientific language differing from the common mode of expression of his day.  He presents his information as a man with his eyes open narrates in a familiar style what he sees.  As civilization spread and science had its representatives in other countries besides Greece, it became indispensable to have a common scientific language, a technical nomenclature, combining many objects under common names, and enabling every naturalist to express the results of his observations readily and simply in a manner intelligible to all other students of Natural History.

Linnaeus devised such a system, and to him we owe a most simple and comprehensive scientific mode of designating animals and plants.  It may at first seem no advantage to give up the common names of the vernacular and adopt the unfamiliar ones, but a word of explanation will make the object clear.  Perceiving, for instance, the close relations between certain members of the larger groups, Linnaeus gave to them names that should be common to all, and which are called generic names,—­as we speak of Ducks, when we would designate in one word the Mallard, the Widgeon, the Canvas-Back, etc.; but to these generic names he added qualifying epithets, called specific names, to indicate the different kinds in each group.  For example, the Lion, the Tiger, the Panther, the Domestic Cat constitute such a natural group, which Linnaeus called Felis, Cat, indicating the whole genus; but the species he designates as Felis catus, the Domestic Cat,—­Felis leo, the Lion,—­Felis tigris, the Tiger,—­Felis panthera, the Panther.  So he called all the Dogs Canis; but for the different kinds we have Canis familiaris, the Domestic Dog,—­Canis lupus, the Wolf,—­Canis vulpes, the Fox, etc.