PRINCIPLES OF TAXONOMY 247 



the sensitive animals, also among the invertebrates; and the intelligent 

 animals corresponding to the vertebrates. Oken (1779-1851), who was a 

 philosopher rather than a naturalist, advocated simultaneously at least 

 two classifications, which were equally worthless. One divided animals 

 into groups according to their systems of organs, as intestinal, muscular, 

 sexual, respiratory, vascular, etc. His other classification was based 

 on the senses. Thus, there were the Dermatozoa (literally, skin or touch 

 animals), by which he meant the invertebrates; the Glossozoa (literally, 

 tongue animals), the fishes; the Rhinozoa (nose animals) which included 

 the reptiles; the Otozoa (ear animals), or the birds; and another class, 

 which appears to have been called interchangeably the Ophthalmozoa 

 (eye animals) or Thricozoa (hair animals), the mammals. It would be 

 hard to name a set of distinctions less applicable as classification marks 

 than most of these, but Oken did not engage in practical matters. Then 

 there was a host of minor systematists the value of whose labors was 

 diminished by attempts to force their classifications into some numerical 

 system, as, for example, those who held that the number of orders in 

 each class should be the same as the number of families in each order, 

 or the number of genera in each family. The favored number was five 

 in some classifications, less often three, four, or seven. 



These early modes of arrangement of animals have been described not 

 for any value that may attach to them as classifications but to form a 

 background for the one system that has survived. It should be obvious, 

 from the brief statements made, that most of the plans used were totally 

 unsuited to the requirements which later developments of zoology would 

 have imposed upon them. The system of Linnaeus, however, was hap- 

 pily capable of being adapted to the demands of the tenets of evolution, 

 and it alone has persisted to the present time. 



The Linnaean System. — That the Linnaean system was rapidly 

 adopted in advance of the general acceptance of the evolution idea is 

 doubtless due largely to the fact that it introduced a sharply defined 

 grouping, a definite terminology, and brief, clear diagnoses. It also 

 permitted early naturalists to group those forms that resembled each 

 other, which would be a natural tendency in any classifier. And then, 

 as stated earlier, came the added advantage that it equally well per- 

 mitted the classification of forms according to their relationships. As 

 stated above, Linnaeus recognized groups of four different values — the 

 class, the order, the genus (plural, genera), and the species (plural, 

 species). To these categories have been added the phylum (plural, 

 phyla) and subphylum (assemblies greater than the class), the subclass, the 

 suborder, the family, the subfamily, the subgenus, the subspecies, and 

 others. Of these additional groups the phylurn and family are now 

 generally accepted, and every classification includes a named group of 



