PBINCIPLES AND PEACTICE OF CLASSIFICATION. 75 
them. The same fancy vitiated all ideas upon the subject of genera, families, and higher 
groups. A genus " was to be discovered in nature, just like a species ; to be named and 
defined. Then species that answered the definition were ''typical"; those that did not do so 
well were '' sub -typical " ; those that did worse, were "aberrant." A good deal was said of 
'' types of structure," much as if living creatures were originally run into moulds, like casting 
type-metal, to receive some indelible stamp; while — to carry out my simile — it was supposed 
that by looking at some particular aspect of such an animal, as at the face of a printer's type, 
it could be determined in what box in the case the creature should be put ; the boxes them- 
selves being supposed to be arranged by Nature in some particular way to make them fit 
perfectly alongside each other by threes or fives, or in stars and circles, or what not. How 
much ingenuity was wasted in striving to put together such a Chinese puzzle as these fancies 
made of Nature's processes and results, I need not say ; suffice it, that such views have become 
extinct, by the method of natural selection, and others, apparently better fitted to survive, are 
now in the struggle for existence. Eightly appreciated, however, the expression which heads 
this paragraph is a proper one. There are numberless types of structure." It is perfectly 
proper to speak of the vertebrate type," meaning thereby the whole plan of organization of 
any vertebrate, if we clearly understand that such a type is not an independent or original 
model conformably with which all back-boned animals were separately created, but that it is 
one modification of some more general plan of organization, the unfolding of which may or 
did result in other besides vertebrated animals ; and that the successive modifications of the 
vertebrate plan resulted in other forms, equally to be regarded as ''types," as the reptilian, 
the avian, the mammalian. Upon this understanding, a group of any grade in the animal 
kingdom is a " type of structure," of more general or more special significance, presumably 
according to the longer or shorter time it has been in existence. An individual specimen is 
*' typical " of a species, a species is " typical " of a genus, etc., if it has not had time enough to 
be modified away from the characters which such species or genus expresses. Any set of 
individuals, that is, any progeny, which become modified to a degree from their progenitors, 
introduce a new type; and continually increasing modification makes such a type specific, 
generic, and so on, in succession of time. There must have been a time, for example, when 
the Avian and Reptilian ' ' types " began to diverge from each other, or, rather, to branch apart 
from their common ancestry. In the initial step of their divergence, when their respective 
types were beginning to be formed, the difference must have been infinitesimal. A little 
further along, the increment of difference became, let us say, equivalent to that which serves to 
distinguish two species. Wider and wider divergence increased the difference till genera, 
families, orders, and finally the classes of Beptilia and Aves, became established. In one 
sense, therefore, — and it is the usual sense of the term, — the "type" of a bird is that one 
which is furthest removed from the reptilian type, — which is most highly specialized by differ- 
entiation to the last degree from the characters of its primitive ancestors. One of the Oscines, 
as a thrush or sparrow, would answer to such a type, having lost the low, primitive, gener- 
alized structure of its early progenitors, and acquired very special characters of its own, repre- 
senting the extreme modification which the stock whence it sprung has undergone. In a 
broader sense, however, the type of a bird is simply the stock from which it originated ; and 
in such sense the highest birds are the least typical, being the furthest removed and the most 
modified derivations of such stock, the characters of which are consequently remodelled and 
obscured to the last degree. Two opposite ideas have evidently been confused in the use of 
the word "Type." They may be distinguished by inventing the word teleotype (Gr. TtXeos, 
teleos, final, i. e., accomplished or determined; formed like teleology , etc.) in the usual sense of 
the word type, and using the word we already possess, prototype (Gr. Trpcoro?, protos, first, 
leading, determining), in the broader sense of the earlier plan whence any teleotype has been 
derived by modification. Tliis, Ichthyornis or Archccopteryx is prototypic of modern birds, 
