PRINCIPLES AND PRACTICE OF CLASSIFICATION. TT 
within the limits of generic relationship. Some of its species are 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 be the most specialized ; tho 
latter, having fewer peculiarities, ure 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 with modification. The application of 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 vertebree, reptile-like teeth, bird-like sternum 
and shoulder-girdle, is a very generalized form. A thrush 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 
type, 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 existing 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, for example, comprehending a majority of all known birds, is scarcely more different 
from other birds than are the families 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 ‘1 the course of time (for it takes time to evolve a class of birds 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 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 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 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 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 follow, from this relation sustained by Mam- 
