CLASSIFICATION OF DIPTERA. 5I 



swiftly moving objects, or in twilight than the other, but 

 the other part better adapted for the formation of a pre- 

 cise image. 



Special nerve structures are present at the base of the 

 halteres, and orienting, auditory and other sense func- 

 tions have been ascribed to these organs by various mor- 

 phologists. Flies from which these organs have been 

 removed are utterly unable properly to direct their flight. 



The internal organs of the reproductive system present 

 some interesting peculiarities. The ovaries of the female 

 consist of an exceptionally large number of egg-tubes. 

 There are three spermathecse, paired accessory organs, 

 and no true bursa copulatrix. The males have two oval 

 testes with short vasa defferentia. The testes are not 

 infrequently colored, possessing a pigment layer. There 

 is a well developed penis with accessory copulatory or- 

 gans. Snodgrass' interesting studies on the comparative 

 anatomy of the external genital organs show that while 

 there may be great variety in these structures among the 

 males of any one family, the females, curious!}' enough, 

 show a remarkable uniformity of the hypopygial organs. 



CLASSIFICATION OF DIPTERA. 



The first real attempt at the subdivision of the order of 

 Diptera was made by Latreille in 1805, when he distin- 

 guished between the nematocerous and brachycerous 

 forms. The term Nemocera was introduced by him in 

 1817, and the characters upon \vhich he based the group 

 are yet employed. The name Brachocera was applied to 

 the remaining Diptera by Macquart in 1834. The char- 

 acters he used, following Latreille, were : 



Antennae at least six-jointed; palpi four or five-jointed. Nemocera. 

 Antennae three-jointed; palpi one or two-jointed. Brachycera. 



This attempt at subdivision, based upon the antennae 

 and palpi, was all that had been made until a compara- 



