28 Transactions of the Society. 



III. — The Mouth-parts of the Nemocera and their Relation 

 to the other Families in Diptera. 



By W. Wesche, F.E.M.S. 



(JXead November 18th, 1903.) 

 Plates III.-VIII. 



The work which I have done on the tropin of Diptera has been 

 mostly concerned with the Muscidse. I have endeavoured to 

 prove : (1) that the palpi, always regarded as maxillary, are in fact 

 labial ; (2) that the whole proboscis homologises with the typical 

 insect mouth ; (3) that the palpi in the Empidse and Syrphidse are 

 homologous, but not homologous with those of the Muscidse, the two 

 former being maxillary, and the latter labial ; (4) I have also formu- 

 lated a rule which enables the observer to discriminate between 

 the palpi of the two parts. " The maxillary palpi when present in 

 Diptera are always in contact with the stipites and cardines of 

 the maxilla?." The application of this rule, and the comparison 

 of a large number of parts, have enabled me to divide nearly all 

 the families of the order into eight groups. 



Several difficulties have been pointed out to me by Mr. A. E. 

 Hammond, F.L.S. (who is well acquainted with the anatomy of 

 the Nemocera), in the Bibionidse, the Tipulidse, and the Chirono- 

 midse ; these I propose to deal with in my remarks on each group. 



In my classification of the families into the different groups, 

 a certain amount of generalisation must be allowed for ; the re- 

 markable diversity of the tropin in the order making this necessary. 

 As it is, genera of the same family, and even the sexes of a species 

 have been placed in different divisions, and I have little doubt 

 but that exceptions, other than those I have noted, will be found, 

 especially among the less known families and rarer species. 



The first group consists of those flies which possess the nearly 

 complete mouth-parts, and are without exception either blood- 

 sucking or raptorial ; mandibles are present, maxilla? lacking the 

 gala?, labium without the palpi, labrum and hypopharynx. As to 

 the epipharynx, it is generally indistinguishable in Diptera, and 

 therefore best omitted ; but I suspect a curious wrinkled mem- 

 brane, lying under the hypopharynx in Simuliwm rcptans L., of 

 being this part. 



