20 THE MODERN STUDY OF ZOOLOGY 



words, the pedigree of the horse has been completely 

 and satisfactorily worked out. 



Another familiar but striking example is afforded 

 by birds. These are very highly specialised forms, 

 and stand apart from other vertebrates in a number 

 of anatomical points. We are now acquainted 

 with a large number of fossil forms serving to 

 connect birds with reptiles, and showing the several 

 gradations by which reptiles gradually lost their 

 teeth, acquired wings and feathers, and became 

 birds. 



If then it is possible by the aid of fossil remains 

 to reconstruct the pedigree of some particular form 

 or group of forms, why should it not be possible 

 for all animals ? As the possibility of this recon- 

 struction gradually dawned on man, so it was slowly 

 realised that such a reconstruction, such a pedigree, 

 would in itself be a perfect system of classification, 

 and the only really natural one. Such a classifica- 

 tion may be spoken of as a genetic or genealogical 

 classification. 



The idea of such a classification is familiar to 

 all of us through the medium of our own special 

 genealogies : these generally take the form of a tree 

 in which the stem represents our earliest ancestor, 

 who, in this country at least, usually takes the form 

 of some impoverished adventurer, whom we should 

 probably be intensely ashamed of could we see him 

 in the flesh, whose sole virtue lies in the fact that 

 he " came over with the Conqueror," and whose 

 sole possessions of any importance appear to have 

 been a crest, a motto, and a coat of arms ; the 



