"The conventional deals with systems of arrangement, classification, orders, families, genera, and the nomenclature, whether of different sections or of individual objects.
"An arrangement should be called systematic, or arbitrary, when it does not conform to the genealogical order taken by nature in the development of the things arranged, and when, by consequence it is not founded upon well-considered analogies. There is such a thing as a natural order in every department of nature; it is the order in which its several component items have been successively developed.[213]
"Some lines certainly seem to have been drawn by Nature herself. It was hard to believe that mammals, for example, and birds, were not well-defined classes. Nevertheless the sharpness of definition was an illusion, and due only to our limited knowledge. The ornithorhynchus and the echidna bridge the gulf.[214]
"Simplicity is the main end of any classification. If all the races, or as they are called, species, of any kingdom were perfectly known, and if the true analogies between each species, and between the groups which species form, were also known, so that their approximations to each other and the position of the several groups were in conformity with the natural analogies between them--then classes, orders, sections, and genera would be families, larger or smaller; for each division would be a greater or smaller section of a natural order or sequence.[215] But in this case it would be very difficult to assign the limits of each division; they would be continually subjected to arbitrary alteration, and agreement would only exist where plain and palpable gaps were manifest in our series. Happily, however, for classifiers there are, and will always probably remain, a number of unknown forms."[216]
That the foregoing is still felt to be true by those who accept evolution, may be seen from the following passage, taken from Mr. Darwin's 'Origin of Species':--
"As all the organic beings which have ever lived can be arranged within a few great classes; and as all within each class have, according to our theory, been connected together by fine gradations, the best, and if our collections were nearly perfect, the only possible arrangement would be genealogical: descent being the hidden bond of connection which naturalists have been seeking under the term of the Natural System. On this view, we can understand how it is that in the eyes of most naturalists, the structure of the embryo is even more important for classifications than that of the adult."[217]
