I'BINCIPLES AND PRACTICE OF CLASSIFICATION. 77 



within the limits of generic relationship. Some of its species arc modified further away than 

 some others are from the generic standard or type to which all conform more or less perfectly. 

 The former, having more peculiarities of their own, are said to he the most specialised ; the 

 latter, having fewer peculiarities, are the least specialized. Those that are the least specialized 

 are obviously the most generalized ; and this means, that we believe them to be nearest to the 

 stock whence all have together descended witli modification. The apidication (jf this illustra- 

 tion to great groups shows us the principle upon which any form is said to be generalized or 

 specialized. The Ichthyornis, with its fish-like vertebra?, reptile-like teeth, bird-like sternum 

 and shoulder-girdle, is a very generalized form. A thrusli is the opposite extreme of a highly 

 specialized form. The two are also separated by an enormous interval of time : one being 

 very old, the other quite new ; a chronological sequence is here perceived. Since the evolu- 

 tionary processes concerned in the modification on the whole represent progress from simplicity 

 to complexity of organization, and therefore ascent in the scale of organization, a generalized 

 tyiie, an ancient type, and a simple type are on the whole synonymous, and to be contrasted 

 with forms specialized, recent, and complex. They therefore respectively correspond to 



"Low" and "High" in the Scale of Organization. — All existhig birds are very 

 closely related, notwithstanding the great numerical preponderance of the class in the present 

 geological epoch. This outbreak, as it were, of birds upon the modern scene, is like the 

 nearly simultaneous bursting into bloom of a mass of flowers at the end of one branch of the 

 Sauropsidan stem. All modern birds, in fact, are strongly specialized forms, so much so that it 

 is difficult to predicate "high" or "low" within such a narrow .scale. The great group 

 Passeres, f(,>r example, comprehending a rna,iority of all known birds, is scarcely more dift'erent 

 from other birds than are the famiUes of reptiles from each other, and among Passeres we have 

 little to go upon in deciding "high" or "low" beyond the musical ability of Oscines. It is 

 hard to see much difference in actual complexity of organization between those birds regarded 

 as the lowest, as an ostrich or a penguin, and those conceded to be highest, as a swallow or 

 sparrow. Nevertheless, in a larger perspective, as between a fish, a reptile, and a bird, the 

 student will readily perceive the bearing of the ideas attached to the terms "low " and "high" 

 in the scale of organization. Creatures rise in the scale by a number of correlated modifica- 

 tions and .' i the course of time (for it takes time to evolve a class of l)irds from sauropsidan 

 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 tli^ " low" general plan 

 of organization ; the culmiuation in man of the vertebrate type, first faintly fiireshadowed in 

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

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

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



As to " evidences of design " in the plan of oi'ganized 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 «'i>ukl 

 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 hind, as is a steam-engine of 

 that kind of an organization ; thcaigh the difference 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 mammals is highest in the scale of organization. The 

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



