The mammals are equal in rank with the classes Birds, Reptiles, Amphibia, Fishes, Round-mouths, and several others formerly re garded as worms or mollusks, all of which i possess one feature of prime importance—a notochord, the prototype of the spinal cord and backbone of the more highly developed forms. This unites these otherwise so varied classes into a still broader aggregation or the Chordate. Beyond this are only two words —Animal and Plant, indicating the two grand kingdoms of life in the world. Even these, however, are so essentially alike in their simplest form, the monad, that they are doubt fully distinguishable at that point of contact, and may be combined under the term organism.
Here, then, ends our inquiry into the place in nature of our example. The animal organ ism called ((cat• is a chordate, eutherian, car nivorous mammal of the family Fender, genus Fells, and species libyca.
Such is the schematic history of a single animal, and it represents not only its place in nature, but its phyllogeny, that is the line of its evolution from a primitive monad to the com plexity and finish of an animal highly adapted to a certain manner of life.
Biological classification is now, therefore, on a sure, philosophical, scientific basis. It has but
one principle — that of descent — blood affinity. The problems are those of perception: to detect the evidence of genetic relationship. To this every fact of investigation, from the embryolo gist's microscope and the anatomist's scalpel to the geologist's hammer and the field-naturalist's notebook, contributes; and no longer is any artificial grouping possible, except on account of an ignorance that study will correct, or as a theoretical suggestion that must be proved before it is acceptable.
In the present article only a single kind of animal has been considered. The process is the same for all others, but different criteria must be employed in the various groupings, and even different terms used, or the same term with different limits. Thus is a far more comprehensive and important group in botany than in zoology. Moreover the diverse temperaments of classifiers lead them to vary in closeness of distinction. Some men see specific or generic differences that others do not admit, wishing to ignore the minute differ ences that the former deem important. The tendency is toward the broader view.