Mr. C. 0. Watcrhousc on the Mouth-organs ofDiptera. 45 



VII. — Some Observations on the Month-organs of Diptera. 

 By Charles 0. Waterhouse. 



Some two years ago I had occasion to study tlie mouth-parts 

 of Diptera, and among otlier books consulted Prof. Lownc's 

 work on the Blow-fly. In his first edition of this book, 

 Prof. Lowne put forward the theory that the proboscis of the 

 Blow-fly is chiefly composed of the maxillie, and not of the 

 labium as usually supposed, and in his new edition he keeps 

 to this view. Prof. Lowne has arrived at this conclusion from 

 studying the development of the parts in the embryo &c. 



Prof. Lowne says : " So far as 1 know there is no dipterous 

 or hemipterous insect in which there are any traces of 

 mandibles, and the parts so named are always a part of the 

 maxillffi, and articulate with the palpigerous scale" (New- 

 Edition, p. 151). The species in which I found the parts of 

 the mouth most perfectly developed is Pangonia longirostrisj 

 and with this insect in view it is impossible for me to doubt 

 that the larger pair of lancets are really the mandibles, and 

 that in spite of the care and skill which Prof. Lowne brings to 

 bear on his investigations, he has nevertheless fallen into 

 some eiTor. Prof. Lowne says : " the only reason for regarding 

 the terminal portion of the proboscis as a modified labium is 

 its position, and this is no evidence from a morphological 

 point of view " (p. 129). This is true, but, so far as I am 

 concerned, it is certainly not position only that influences me 

 in my determination. \Vith Prof. Lowne and others I consider 

 the slender pair of lancets in Pangonia to be the maxillaj j 

 this is clear enough from the presence of the maxillary palpi. 

 The larger pair I consider to be the mandibles, not only on 

 account of their position (although this is just what it ought 

 to be), but because they appear to have a distinct origin from 

 the more slender pair, and the structure of the base with its 

 produced basal angles is only a slight modification of the form 

 constantly met with at the base of the mandible. I would 

 especially compare it with the mandible of the Australian 

 Neuropterous insect Bittacus. 



It is somewhat difficult to understand exactly what Prof. 

 Lowne does consider these larger lancets. He speaks of them 

 as " parts of the maxillai " without saying what part. If 

 they are parts of the maxillae, I presume they are either the 

 lacinijB or galeae. 



This, however, does not seem to be Prof. Lowne's view, for 

 in speaking of Pulex he says, the pseudolabium is "formed by 

 the united galeae of the maxilla " (p. 1 52) ; and if the " pseudo- 



