PRINCIPLES AND PRACTICE OF CLASSIFICATION. 75 



tliein. The same faucy vitiated all ideas upon the subject of genera, families, and higher 

 groups. A "genus" was to be discovered in nature, just like a species; h> be named and 

 defined. Then species tliat answered tlie defiuitlDU were "typical"; those that did not d(i so 

 well were " sub -typical " ; those that did worse, were "aberrant.'' A good deal was said of 

 "types of structure," much as if living crcatvu-es we're origiuaily run into iiKnilds, 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 buxes them- 

 selves being supposed to be arranged by Nature iu some particular way to nuike them tit 

 perfectly alongside each other by threes or lives, or in stars and ch-cles, 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 (ithers, apparently better fitted to survive, are 

 n<j\v in the struggle for existence. Ivightly appreciated, however, the expression which heads 

 this paragraph is a proper one. There are numberless " types of structure." It is jierfectly 

 proper to speak of the " vertebrate type," meaning thereby the whole plan of organization of 

 any vertebrate, if we (dearly understand that such a type is not an independent or origintd 

 model conformably with which all back-boned animals were separately created, but that it is 

 one modification of some more general plan iif organization, the uid'olding of which may or 

 did result in other besides vertebrated animals; and that the successive modifications (jf the 

 vertebrate plan resulted in other forms, eiiually to lie regarded as "types," as the reptilian, 

 the avian, the mammalian. Upon tliis 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 enougli to 

 be modified away fi-om 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 specifie, 

 generic, and so on, in succession of time. There must hiive been a time, for example, when 

 the Avian and Reptilian " types" began to diverge from each other, or, rather, to branch apart 

 from their comnmn ancestry. In the initial step of their divergence, when their respective 

 types were beginning to be formed, the difl'erence 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 Reptilia 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 diftc]-- 

 entiation to the last degree from the characters of its primitive ancestors. One of the Oscliies, 

 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 wlrenci; it sprung has undergone. In a 

 broader sense, however, the type of a bird is simidy tlie stock from which it originated ; and 

 in such sense the highest birds are the least typical, lieing 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 A^-ord feleofi/pe (Gr. rfXeos-, 

 teleos, final, i.e., accomphshed or determined; formed like tehologii, etc.) in the usual sense of 

 the word type, and using the woi-d we already p(jssess, }}rotottjpe (Gr. Trpmrot, protos, first, 

 leading, determining), in the broader sense of the earlier plan whence any teleotypie has been 

 derived by modification. Thi,s, Ichthyornis or Archa:opter>jx is prototypic of modern birds, 



