252 W. WESCHE. 



characters of the interior and more invisible parts, which I have 

 formulated in a previous paper. 1 They will be described as of 

 certain types: 



Type i. A long flagelliform tube, as in Tipula, or an approxi- 

 mation to that type. 



Type 2. A prominent chitinous bulb, with lateral processes, 

 as in Ptychoptera. 



Type j. A low membranous process supported by chitinous 

 levers, as in Gymnoplista and Culex. 



In the second case the nature of the ancillary claspers are given 

 (a) as simple hooks, as in many Muscidse, (&) jointed, as in the 

 Tabanidse, (c) or a simple unsegmented cercus-like appearance, 

 as in the Bibionidse. Three types of ovipositor are differentiated : 



Type i. Telescopic or protrusile, as in Calliphora or Doli- 

 chopus. 



Type 2. Nontelescopic, as in Tipula, where it can scarcely 

 be said to exist. 



Type j. Short segmented, such as is found in the Empidse. 



Further the appendages of the egg-guide are tabluated, as (a) 

 cercus-like, as in Bibio or Musca; (b) uncinate, as in Tipula or 

 many Muscida?; (c) styliform, as in Psychoda or Pipunculus, 

 where it is probably a fusion of the pair of forceps. 



The number of receptacula is noted. The types of penis 

 and ovipositor seem to me the more important characters. 

 Among the characters of the eyes, holopticism, dichopticism, 

 and the greater width of the female front are given; and the 

 absence or presence of ocelli is also noted. 



It may be stated that in certain families the compound eyes 

 are chitinous plates pierced by circular facets or lenses; this 

 opaque structuie is much reduced in other families till only 

 strips of chitin separate the hexagonal facets. Finally in 

 specialized groups all traces of opaque structure are lost. 



These tables may be examined in two ways. The most im- 

 portant characters may be noted and the tables consulted to see 

 how far they are in agreement; or the characters of the group 

 may be added up and averaged. The latter method shows that 



*" Notes on the Value of the Genitalia in Phylogeny." Trans. Entom. Soc, 

 London, 1908. 



