no INTBOUUCTION. 



is towards their entire loss, and in the more highly specialized 

 families there is never more than one joint." 



At the tip of the proboscis, or ver^^ near it, is a pair of larger 

 or smaller organs, generally distinctly visible, and more or less 

 oval in shape, known as the lahelhi or lips. Their function varies 

 considerably, in some groups representing merely an apparatus 

 for holding, in others they are evidently sense-organs, being "pro- 

 vided with hairs inserted in small semi-translucent* spots on the 

 outer sides and margins." This is the case in most tlower- 

 haunting flies, Hyrphid.?: for example. In the majority of Diptera 

 the labella are of fair or considerable size, and are provided with 

 radiating ridges on the inner opposable sides. These pseudotrachece, 

 as they are called, " serve as a means of attrition, by which the 

 insect rubs off particles oi^ food from firm substances." In at 

 least one family, the Asilid.i, they are rigid and horny. " Some- 

 times the labella are long and slender, and are folded back under 

 the labium when at rest." 



The mouth-parts in some Diptex'a are quite rudimentary, attain- 

 ing their most abortive state in the CEsTRiu.i:, in which they are 

 almost absent. 



TJie antenna'. — These organs exhibit a wider range of variability 

 than any other in the Diptei-a, and to the beginner offer many 

 puzzles, although a moderate amount of study will enable one 

 to discriminate between the nematocerous, bracliycerous, and 

 muscid types, of which the latter is somewhat quickly recognised, 

 although some 8yrphid antennae may easily be confused with it 

 at first sight. 



As a means of classification the antennae have always been 

 regarded as furnishing one of the most fundamental characters. 

 It is significant that so long ago as 1802, when Latreille made the 

 first real attempt at classification by dividing the Diptera according 

 to the palpal and autennal characters, the long filiform nature of 

 the many-jointed antennae, combined with the elongate four- or 

 five-jointed palpi, was seen to be typical of the Nematocera. (this 

 term being introduced by Latreille in 1817) ; whilst the short 

 three-jointed antennae, coupled with the one- or two-jointed short 

 palpi, of the rest of the Diptera were acknowledged as t^he charac- 

 teristics of the Bbachycera, the latter term having been pro- 

 posed by Macquart in 1825. The valuable systematic characters 

 contained in the venation did not occur to dipterologists until 

 years afterwards. 



In the Nematocera the antennae are always more or less elon- 

 gate,* often conspicuously so, composed normally of eight to 

 sixteen distinct joints ; in a few cases, as in some males of species 

 of Eriocera in Tipulid^, of six joints only ; and in some other 

 instances, of as many as twenty-eight: in fact some authors have 



* With tlie exception of ORPHNEPiiiLiDyE, a group of only five species 

 representing a single and altogether anomalous genus. 



