86 Annals Entomological Society of America [Vol. VIII, 
cases in which they confused distinct genera or referred them 
to wrong groups were due to no fault of perception, but rather 
to the fact that they had no sure guide to the value of certain 
slight but constant external adult characters. At the present 
day we are fortunate to possess such guide in the male and 
female reproductive system, egg and first-stage maggot charac- 
ters. 
The errors of the specialists are, on the whole, comparatively 
few and not appalling; while, the causes thereof being recognized, 
their repetition may be avoided. All favored closely restricted 
generic concepts. 
Let us now turn to the muscoid work of those general dip- 
terists who have passed into history. All of these employed 
broad as opposed to restricted generic concepts. Macquart, 
Schiner and Wulp are very important and significant in this 
connection. Walker, Bigot and Coquillett stand more or less 
apart from them, but are even more significant. None of these 
authors can claim the title of muscoid specialist. 
The generalists attempted to apply the same broad generic 
concepts to the Muscoidea that they applied to the rest of the 
Diptera. Without going into lengthy detail, it is enough to 
state that their mistakes are many and often overshadow the 
good contained in their results. Their misidentifications of 
species are extremely numerous. Their wholesale confusion 
of distinct generic forms was the natural result of no concise 
generic concepts. Almost throughout, their genera are mixed- 
genera. They may be said to have practically lacked muscoid 
generic concepts, for their generic rulings were largely arbitrary 
and so loose as to admit numerous foreign elements. The true 
explanation of all this is that they possessed only the most 
superficial knowledge of their subject. I wish to add that these 
statements can be fully substantiated. 
History, therefore, testifies to the necessity for restricted 
generic concepts in the Muscoidea. After many years of in- 
tensive study of these flies, I can see this necessity more clearly 
every day. There is no question whatever of the necessity, 
either in theory or in practice, but I seek to present some 
tangible and specific reasons in demonstration. 
Investigation of this subject demands consideration of 
several principles, namely, phylogenetic orientation, environ- 
mental adaptation including habitus-convergence, inheritance 
