126 



AN ACCOUNT OF BRITISH FLIES. 



bases his classification and specific characters on the sexual organs, 

 viz., the Hypopygium or $ copulatory organs, and the ovipositor 

 (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 Hypopygium and 

 Ovipositor (of the genus Phronia). 



The Hypopygium (Fig. 24). This is composed of the following 



Fig. 24. — $ genitalia = hypopygium of Phronia. I. and II. A = laminffi basalis ; 

 B = lam. superte ; c = forceps superior, D forceps inferior ; III. := forceps superior. 



parts: (i.) lamina Imsalis ; (\\.) lainiim superce ; (m.) forceps inferior ; 



{\v.) forceps superior ; (v.) and the appendix interna, or adminiculum. 



(i.) The lamina 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 



