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126 AN ACCOUNT OF BRITISH FLIES. 
bases his classification and specific characters on the sexual organs, 
viz., the Hypopygium or g copulatory organs, and the ovéipositor 
(Legerohre or? ), The great importance of these two parts cannot 
be over-estimated, as they form the most decisive specific characters. 
The colour and nervation of the wings, etc., cannot be relied on, 
especially in the Mycetids, where the variation seems to be very great, 
and although, as pointed out by Professor Mik, the use of the 
hypopygium and ovipositor as specific characters necessitates the 
destruction of the species, it is far better to do so and thus find out 
what the true species are, than to be adding numbers of species, 
which are mere variations in colour and nervation. Is it not far 
better to have the hypopygium or ovipositor of an insect identified 
than the perfect fly which we cannot definitely identify? The great 
importance of these organs cannot be valued enough as specific dis- 
tinctions. I will now give an account of the Aypopygium and 
Ovipositor (of the genus Phronia). 
The Aypopygium (Fig. 24). This is composed of the following 
Fic. 24.—d genitalia=hypopygium of Phronia. I. and II, A=laminz basalis ; 
B=lam. supere ; C= forceps superior, D forceps inferior ; III. = forceps superior. 
parts : (i.) Zamina basalts ; (ii.) damine supere ; (iii.) forceps inferior ; 
(iv.) forceps superior ; (v.) and the appendix interna, or adminiculum. 
(i.) The Zamina basalis, which forms the greater part of the 
hypopygium, is attached to the sixth abdominal segment 
by the modified two last segments (seventh and eighth). 
The posterior surface of the lamina is indented in various 
