114 GENERAL ORNITHOLOGY tart ii 



therefore, the length of time a character has been in existence, and 

 its taxonomic value, are correlated, and each is the exponent of the 

 other. 



"Types of Structure." — In no department of natural history 

 has the late revolution in biological thought been more effective 

 than in remodelling, presumably for the better, the ideas underlying 

 classification. In earlier days, when " species " were supposed to be 

 independent creations, it was natural and almost inevitable to 

 regard them as fixed facts in nature. A species was as actual and 

 tangible as an individual, and the notion was, that, given any two 

 specimens, it should be perfectly possible to decide whether they 

 were of the same or different species, according to Avhether or not 

 they answered the " specific characters " laid down for 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 crea- 

 tures were originally run into moulds, like casting type-metal, to 

 receive some indelible stamp ; Avhile — 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. Kightly appreciated, how- 

 ever, 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 organisation of any vertebrate, if we clearly understand that such 

 a type is not an independent or original model conformably with 

 which all backboned animals were separately created, but that it is 

 one modification of some more general plan of organisation, the un- 

 folding 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 struc- 

 ture," of more general or more special significance, presumably 



