TAXONOMY OF MUSCOIDF.AX FUKS — TOWNSEND 'j 



superfamilies, but also a great mass of the intermediates, intergrades, 



and intergradants that have resulted during the long-continued 

 process of the evolution of these types. 



Brauer and von Bergenstamm recognized these conditions in the 

 Muscoidea and treated the superfamily accordingly. As being 

 highly apropos of this subject, the following remarks are quoted 

 frum the translation of these authors' Introduction (published in 

 Psyche, vol. vi, pp. 313-16, and 329-32), the whole of which can be 

 studied with much profit : 



"It is a fundamental principle in the development of the whole 

 dipterous stock that, from the lowest {Orthorrhapha nematocera) 

 to the most differentiated or highest (Cyclorrhapha schisometopa) , 

 the actual value of the genus, and of the systematic series generally, 

 becomes less and less. This proposition seems applicable to all 

 groups of animals — in all cases the most recent forms are more 

 closely related and more difficult to characterize .than older ones. 

 The cause lies in the numerous intermediate forms occur- 

 ring in a group of animals which has just reached its period of great- 

 est prolificness." 



As the same authors point out farther along in their Introduction, 

 it is absolutely futile to attempt a classification of these flies along 

 any other lines than a separation into many comparatively restricted 

 categories. The authors are also correct in maintaining that the 

 classification of all animals must be based on the entire develop- 

 ment — not on the adult alone. The characters of the imago are most 

 important for genera and species ; those of the earlier stages are 

 most important for families and higher categories, even up through 

 orders and classes. In studying early stages, it may be pointed out 

 that some characters will occasionally serve for generic separation, 

 but much judgment must be exercised in deciding which characters 

 are of value for this purpose, since conspicuous ones may in some 

 cases possess less than generic value. Such are those of special 

 adaptation to peculiar conditions of life. 



The fact should be recognized, as suggested in the opening text 

 to this chapter and emphasized in the quotation just given, that gen- 

 eric values are not necessarily uniform throughout the organic 

 world. It is fallacious to attempt to set a standard whereby plant 

 and animal genera, or animal genera alone, shall be gauged by a cer- 

 tain fixed measure of difference. This holds good even in different 

 superfamilies of the same order or suborder of insects. The de- 

 mands of the group in hand must be considered in each case. A 

 superfamily in the multiform stage of development, contingent upon 

 its being still in process of evolution, demands a less generic value 



