336 



JOHN B. SMITH. 



palpus, seen at the left of the figure in its relation to the palpifer, is 

 completely separated by muscular attachments, while retaining a 

 close proximity to it, so that the relationship is easily manifested. 



In a common muscid species, perhaps a Liicilia, with bright, shiny, 

 yellowish to green bronze thorax, we note a still further separation 

 of palpus from the palpifer, and a more complete 

 specialization of the latter organ. The palpus now 

 retains no apparent relation to the chitinous ])arts 

 of the mouth, the base arising from a more chitin- 

 ized strip of the enveloping membrane. Of the 

 piercing character of the palpifer so little trace 

 remains, that its true character could not be sus- 

 pected without a study of the species previously 

 figured. In fact, there is now a complete change 

 of function, for I attribute to this part a prominent 

 share in the flexion of the proboscis. The part is 

 Fig iQ Operculum "^^ ^^^^ ^^ ^"7 ^pccics examined by me, in which 

 and palpifer of 5/*;^- the mouth parts are rigid, like Tabanus, SimuUum, 

 rop oria cy in rica. ^^.^1^^. qj. Qulex, though iu the latter there may be 

 a small basal prolongation similar to that of Bombylhus. Here, the 

 flexion is a very limited one, however, unaccompanied by any re- 

 traction. In forms like Leptis and Stratiomyia, where there is mere 

 retraction without flexion, there is no basal pro- 

 longation whatever, and, as no piercing effects are 

 required, there is a simple reduction in size, without 

 any change of function. In the development of 

 what may be termed the muscid type, in which the 

 mouth parts become entirely enveloped in a mem- 

 braneous extension of the oral opening, and the 

 sac thus formed becomes entirely retractible within 

 the head, a new adaptation becomes necessary. 

 The character of the mouth has changed ; piercing 

 organs are no longer required ; the palpifer, from 

 its situation as the exterior part of the maxillate 

 structure, gives the greatest opportunity for lever- 

 age and the modification begins in the direction of 

 a process for attaching the muscles. It is notable that, in the be- 

 ginning, the basal process is short, broad and flattened, strongly 

 roughened for the muscular attachments ; a mere appendix to the 

 functionless, but still well developed piercing organ. As the devel- 

 opment progresses the piercing organ becomes smaller, until it is 



Fig. 20. Fulcrum 

 and palpifer of Lu- 

 cilia sp. 



