PRINCIPLES AND PRACTICE OF CLASSIFICATION. 77 



stock as really as it does to develop the germ of an egg into the body of a chick). Progressive 

 differentiation and specialization of structure and function in due course elaborates diversity 

 from sameness, complexity from simplicity, the " high " special from the " low " general plan 

 of organization ; the culmination in man of the vertebrate type, first faintly foreshadowed in 

 the embryonic Ascidian. No one should venture to foretell the result of infinitesimal incre- 

 ments in elevation of structure and function, nor presume to limit the infinite possibilities of 

 evolutionary processes, either in this actual world or in the foretold next one. 



As to " evidences of design " in the plan of organized beings, it may be said simply that 

 every creature is perfectly " designed " or fitted for its appropriate activities, and perfectly 

 adapted to its conditions of environment. In fact, it must be so fitted and adapted, or it would 

 perish. Whether it so determines itself, or is so determined, is a teleological question. The 

 truth remains that every creature is perfect in its own way. A worm is as perfectly fitted to be 

 a worm, as is a bird to be a bird ; in fact, were it not, it would either turn into something else, 

 or cease to be. A spade is as perfect an organization of the spade kind, as is a steam-engine of 

 that kind of an organization ; though the di2"erence in complexity of structure and functional 

 capacity, like that between the lowly organized ascidian generality and the highly organized 

 avian speciality, is enormous. 



One word more : The class of mauimals is highest in the scale of organization. The 

 class of birds is next highest. But it does not follow, from this relation sustained by Mam- 

 malia and Aves collectively, that every mammal must be more highly organized than every 

 bird. It is difficult to say how a mole or a mouse is a more elaborate or more capable creature 

 than a canary-bird, physically or mentally. The relative rank of two groups is determined by 

 balan(;ing the aggregate of their structural characters. In large series, the average of devel- 

 opment, not the extremes either way, is taken into account ; so that the lowest members of a 

 higher group may be below the highest members of the next lower group. The common phrase, 

 " below par," or '' above par," is most applicable to such cases. 



Machinery of Classification, — The inexperienced student may be glad to be given some 

 explanation of the way in which the taxonomic principles we have discussed are applied, and 

 carried into practical effect in classifying birds. Our machinery for that purpose is our inherit- 

 ance from those naturalists who held very different views from those which touch the evolu- 

 tionary key-note of modern classification. It is clumsy, and does not work well as a means of 

 expressing the relations we now believe to be sustained by all organisms toward one another ; 

 but it is the best we have. Systematic zoology, or the practice of classification, has failed to 

 keep pace with the principles of the science ; we are greatly in need of some new and sliarper 

 " tools of thought," which shall do for zoology what the system of symbols and formulae has 

 done for chemistry. We ivant some symbolic formidation of our knowledge. The invention of 

 a practicable scheme of classification and nomenclature, which should enable us to formulate 

 wliat we mean by Merula migratoria, as a chemist symbolizes by SO4H2 what he understands 

 liydrated sulphuric acid to be, would be an inestimable boon to working naturalists. The 

 mapping out of groups with connecting lines to indicate their genetic relations, in the form of a 

 " phylum," is a common practice ; but that, like any other pictorial representation of a " family 

 tree," is not the graphic symbolization required. We already have a mother of the required 

 invention in the necessity of the case, and may ho])e that the father will not be long in 

 coming. 



Under the present system, Birds are called a " Class " of Vertebrates, and are subdivided 

 into " orders," " families," "genera," "species" and " varieties," as already sufficiently indi- 

 cated. Groups intermediate to any of these may be recognized ; and if so, are usually distin- 

 guished by the prefix sub-. Many other terms are in occasional use, as " tribe," " race," 

 "series," "cohort," "super-family;" but those first mentioned are the best established ones 



