Evolution and Taxonomy 41 



a statement of the method I propose for appljdng the theorj' 

 of natural selection to taxonomj' more fully than has been 

 done before. 



As the structure of a highly organized animal or plant is too 

 complicated to be understood in detail at once, it is suggested 

 that the student begin with the study of a single organ 

 possessed by the members of the group to be classified, and 

 that his studies take the following course : First the variations 

 in form of this organ should be observed, including palaeonto- 

 logical evidence if possible ; then its function or functions 

 should be determined. With this knowledge endeavor to de- 

 termine what was the primitive form of the organ and the 

 various ways in which this primitive form has been modified, 

 keeping in mind the relation of the changes in form of the 

 organ to its function. In other words endeavor to read the 

 action of natural selection upon the group of organisms as it 

 is recorded in a single organ. The data thus obtained will 

 aid in making a />rt)z'wz(3«a/ classification of the group. 



When this stage has been reached another organ should be 

 selected and its history worked out in a similar way. 



The results of the two investigations should then be com- 

 pared ; and where they differ there is indicated the need of re- 

 newed study. For if rightly understood the different records 

 of the action of natural selection will not contradict each 

 other. The investigation should be continued by the study 

 of other organs and a correlating of the results obtained until 

 a consistent history of the group has been worked out. 



This method differs from that commonly employed in being 

 a constant effort to determine the action of natural selection 

 in the modification of the form of organisms in order to better 

 adapt their parts to preform their function. Ordinarily little 

 or no attention is devoted to the study of the functions of 

 organs in purely taxonomic works. 



If the history of a group be worked out in the manner indi- 

 cated, the student will feel the need of recording his results in 

 such a way as to indicate the phylogeny of the divisions of the 

 group. But as the necessities of book making require a linear 

 arrangement of descriptions this is somewhat difficult ; for the 



