A NEW APPLICATION OF TAXONOMIC PRINCIPLES. 



By Charles H. T. Townsend, Lima, Peru. 



Scarcely more than half a century has passed since the 

 belief was generally entertained as indisputable that species 

 and other taxonomic categories were fixed and unchangeable 

 entities. The basic elements of current taxonomy date a 

 century farther back. 



Our taxonomic system was founded on the principle of 

 permanency in organic morphology, without any idea of 

 change and evolution. In its original concept and application 

 it was therefore inelastic and not in accord with the facts. We 

 have been constantly endeavoring, however, to apply this 

 inelastic system to the elastic morphology of living matter. 

 The result is a demonstration of incompatibility between the 

 two. 



Any taxonomic system must be arbitrary and fixed in 

 certain of its fundamental aspects, but it must also accord 

 with phylogenetic facts. A radically new system is not here 

 proposed, but merely a modification of the current system to 

 fit the phylogenetic facts that we find today. It is not held 

 that living matter is morphologically changing with such 

 rapidity that it needs a system which will change within a 

 lifetime in order to keep up with the progress of evolution. 

 But it is held that living forms exhibit distinct phylogenetic 

 phases according to the age of the stocks of which they form 

 a part, and that this fact must be taken into account in their 

 taxonomic treatment. 



No stock is today changing rapidly enough in nature for us 

 to note the specific steps of change. But if we pass all stocks 

 in phylogenetic review we are struck most forcibly with the 

 successive but gradual change of conditions exhibited as we 

 proceed from the oldest to the youngest stocks. In such re- 

 view we get an instantaneous reflection of the bimorphologic 

 changes which take place in time. 



It has fallen to the lot of the writer to make a critical study 

 of the morphology and phylogeny of the muscoid flies, which 

 undoubtedly comprise some of the youngest stocks of insects, 

 and to attempt to establish a taxonomic treatment of them 

 which shall accord with their morphology and phylogeny and 



226 



