222 ME. W. WESCHfi ON THE LABIAL AKD 



shape and are continued along the sides of the main trachese. The central plate seems 

 to he detached, hut that the parts are homologous with those in CalUphora (PI. 8. fig. 7) 

 is evident. 



3. Maxillce. — Again examining CalUphora we find that, in addition to the mandibles, 

 the maxillae, which are present in the Syrphidse and Empidae, have disappeared. But if 

 the base of the labium is dissected, the cardines of the maxillse will be found embedded, 

 and working the labrum as levers (PL 8. fig. 4). That these are cardines of the maxillae 

 may be proved by comparing the parts with those in IJristaUs and Helophiltis (PI. 8. 

 figs. 3, 5, & 6). A comparison with Culea- pipiens only strengthens this proposition 

 (PI. 9. fig. 24) *. 



We also find the palpi in a different position. In CalUphora they are above and 

 posterior to the base of the labrum ; in Empis and Eristalis they are in a more anterior 

 position and firmly attached to the cardines of the maxillae (PI. 8. figs. 2, 3, & 4)f. 

 A dissection of the maxillae in Helophilus pendulus and Eristalis tenax shows the palpi 

 attached to the maxillae by a membrane, which has at its extremity a chitinous plate, 

 w hich is probably the palpifer. The bases of the palpi connect wuth the maxillae just 

 before they emerge from the enclosing membrane of the labium. There are well-marked 

 ridges halfw^ay down the maxillae that indicate the boundary of the cardo. The laciniae 

 continue, the galas having aborted. The palpifer shows only on the palpus, being pulled 

 apart from the maxilla (PI. 8. figs. 6 & 6). Further, I have dissected the maxillae in 

 Culex piipiens, 2 (PI. 9. fig. 24), in Tabanus bromius, T. sudeticus, Chrysojjs ccecutiens, 

 Asilus crabroniformis, and a species of SimuUum, all species with a nearly complete 

 armature, and I find that invariably the palpus is firmly attached to the stipes and cardo 

 of the maxilla. 



4. Labium. — The palpi in the Muscidae are in quite a different position, attached to 

 the membrane of the labium ; at their bases in CalUphora are plates of chitin and rows 

 of two or three bristles. The palpi have no connection with the levers of the labrum, 

 which, as w^e have seen, are the cardines of the maxillae in Eristalis. They are there- 

 fore labial and not maxillary palpi, and have worked round from a lower part of the 

 labium to the upper. The chitinous plates and rows of bristles in CalUphora have their 

 analogies in a great number of related species. In some the chitin is evident, in others 

 it has almost disappeared, but the row of bristles is very constant, and can be seen in all 

 the species possessing labial palpi that I have examined. It is fairly obvious that these 

 parts represent the palpiger. 



5. A dissection of the trophi of Culex pipiens throws some light on the subject under 

 discussion. In both sexes the labium is simply a chitinous sheath for the lancets. In 

 its paired and segmented flaps may be seen the homologies of the labella. 



The cardines and stipites of the maxillae are present, having much the same appearance 

 as in the Muscidae, and a palpifer can be traced supporting the three-jointed palpus 

 (PI. 9. figs. 23 & 24). 



* 8ee note on page 229. 



t The stipes and cardo are so soldered together that it is not possible, in the majority of cases, to define them. 

 The palpifers are attached to the stipites and not the cardines. 



