XXVIII INTRODUCTION. 



that shown by insects of other orders, as the Coleoptera, 

 Lepidoptera and Hynienoptera, which have but two thoracic 

 ganglia. In these insects, however, it is the two posterior 

 ganglia (nieso and metathoracic) wliieh are fused into one. 



The careful studies of Child on the so-called Johnston's 

 organ, an elaborate structure of fine chitin rods connected 

 with special nerve cells and these connected by fine nerves 

 with the main antennal nerve, the whole organ (which is lo- 

 cated in the second antennal joint) seem to ascribe definitely 

 an auditory function to the antennae. Child's studies were 

 mostly made on the Nematocerous forms. 



Special nerve structures are present at the base of the hal- 

 teres, and orienting, auditory and other sense functions have 

 been ascribed to them by various morphologists. 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 

 consists of an exceptionally large number of egg-tubes, there 

 are three receptaculi seni'iiiales, paired accessory glands, and 

 no true bursa copulatrix. The males have two oval testes with 

 short vasa^tferentia. The testes are not infrequently color- 

 ed, possessing a pigment layer. There is a well developed 

 penis with accessory copulatory organs. 



Classification of Dii'Tp:ua. 

 The first real attempt at the subdivision of the order of 

 Diptera was made by Latreille in 1802, when lie distinguished 

 between the Nematoeerous and Brachycerous forms. The 

 term Nemocera was introduced by him in 1817, and the char- 

 acters upon which he based the group are yet employed. The 

 name Brachycera was applied to the remaining diptera by 

 Macquart in 1825. The characters he used, following La- 

 treille, were : 



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



Antennic tiiree-jointed ; palpi one or two-jointed. Brachycera. 



