BRAUER ON GENERIC VALUES IN THE MUSCOIDEA. 
By FREDERICK KNAB, 
Bureau of Entomology. 
The idea seems to prevail with some American writers on 
Muscoidea, that generic and specific values can be standardized, 
that is, that the validity of genera and species should be made 
dependent upon the amount of difference. Such practice, 
dictated merely by convenience and the limitations of the work- 
er, manifestly does violence to the facts in nature; it could be 
ignored as unscientific, were it not so generally advocated. 
Moreover, the inevitable result of confusing poorly defined 
species or genera is to invalidate such data as have been pub- 
lished upon them, from both a purely scientific and an economic 
standpoint. Thus, Dr. Townsend has shown me that flies, 
which according to the accepted “‘system’”’ are one species, lay 
very different eggs or have remarkably distinct first-stage 
larve, that indicate, at the least, wide differences in biology. 
It is a well recognized and generally accepted principle, that 
recent groups have less clearly marked species and genera than 
the more ancient groups, where the intergradient forms have 
dropped out. In the Muscoidea we have such a recent group 
and the great diversity of modifications presented makes the 
problem of establishing a natural classification, that is, one 
that follows the phylogeny, an extremely difficult one. Fried- 
rich Brauer, who, in spite of many adverse criticisms, remains 
one of the greatest exponents of the Diptera, clearly perceived 
this, as is shown by the following translation of a passage in his 
early paper on the systematic significance of the larval char- 
acters of the Diptera, published forty-five years ago.* 
“In surveying the larval forms, one perceives at once that 
the genera and families of the orthorhaphous Diptera are far 
more sharply characterized, that is, have a higher systematic 
value, than the Cyclorhapha, among [the imagines of] which 
occurs the greatest diversity within the narrowest limits. 
While with the Orthorhapha the majority of the families can 
*Kurze Characteristik der Dipteren-Larven zur Bekraftigung des neuen von. 
Dr. Schiner entworfenen Dipteren-Systemes. Verh. zool.-bot. Ges. Wien, vol. 19, 
pp. 843-852 (1869). 
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