38 John Henry Corns tock 



standing of the processes by which new forms have arisen. 

 The object of taxonomy will not be a mere grouping of forms 

 according to similarity of structure. But the systematist will 

 have constantly before him the question : What do these vari- 

 ations of form mean ? With this change in the object of tax- 

 onomic work, there will come a change in its methods. It is 

 strange that the change has been so long delayed ; for we are 

 really using the same methods that were employed before the 

 establishment of the truth of the theory of natural selection. 

 What these methods are was indicated by Darwin in the fol- 

 lowing words : 



"Practically, when naturalists are at work, they do not 

 trouble themselves about the physiological value of the char- 

 acters which they use in defining a group or in allocating any 

 particular species. If they find a character nearly uniform, 

 and common to a great number of forms, and not common 

 to others, they use it as one of high value ; if common to 

 some lesser number, they use it as of subordinate value." 

 (Darwin, Origin of Species, pp. 367-368, Am. Edition.) 



This statement is about as true to-day as when Darwin 

 wrote it. For if one will look through the taxonomic works 

 on zoology or botany he will very seldom find any reference 

 to the functions of organs. But almost all naturalists now 

 believe that in each epoch of time the forms of existing or- 

 ganisms have been determined by a survival in preceding 

 generations of those individuals whose parts were best fitted 

 to perform their functions. 



Does it not follow from this belief that we can confidentl}' 

 expect to gain much help in our efforts to work out the phy- 

 logeny of organisms by making a careful stud}^ of the func- 

 tions of their organs, and endeavoring to understand the rea- 

 sons for the action of natural selection ? 



I suggest, therefore, that the logical way to go to work to 

 determine the affinities of the members of a group of organ- 

 isms is first to endeavor to ascertain the structure of the primi- 

 tive members of this group ; and then endeavor to learn in what 

 ways these primitive forms have been modified bj^ natural 

 selection, keeping in mind that in each generation those 



