EEDUCTION OF PALPI 53 



with the maxillary palpi, it is different when the palpi consist of only two, or 

 even of a single joint, as is the rule in the Diptera, for there will then be no 

 joint left to explain as maxillary palpus. I therefore prefer to regard the palpi 

 of the Diptera as homologous with the entire maxillae of other insects, only that 

 they are oftenest unjointed and not divided into different components. Only in 

 Simulium, Tipula, and Limmohia I have thought to find an indication, in the 

 before mentioned appendix at the base of the palpi, of the different working 

 divisions of the exponents of the second metamere of other insects." 



The palpi are variously modified in the different forms. In Anopheles and in 

 the males of a great many other forms the palpi about equal the proboscis in 

 length, or even exceed it. In most of these forms the palpi are slender, particu- 

 larly in their proximal halves, and furnished with false joints to increase their 

 flexibility so that they can be folded back when the insects are feeding. 



In MegarhinUrS, however, where the palpi are less in the way, on account of the 

 downward-curved proboscis, they are stout and quite rigid, without basal false 

 joints, and the joints are armed near their apices with heavy spines. In the 

 males of Anopheles and of most species of Culiseta the palpi are enlarged 

 apically into a distinct club. In Anopheles the club is composed of the outer 

 two joints, while in Culiseta it may be composed of these same two joints or of 

 the last joint alone. 



In the males with long palpi of many species of Culex and A'edes the outer 

 half of the palpi is more or less thickened and densely hairy, the last joint, how- 

 ever, generally tapering to a point ; the last two joints are usually curved upward. 



In Megarhinus and Bancroftia we begin to get a reduction in the female palpi, 

 and this occurs principally in the terminal joint. In the American species oi 

 Megarhinus the palpi of the female are about two-thirds the length of the pro- 

 boscis, while in the Old World species of this genus the reduction has gone still 

 farther and they are sometimes less than one-fourth the length of the proboscis. 

 In the females of both the New and the Old World species of Megarhinus there 

 is a minute terminal joint, and the number of joints is the same. 



In Bancroftia the palpi of the female are about two-fifths the length of the 

 proboscis, the terminal joint small; in the case of one species (B. fascipes) the 

 terminal joint is about three times as long as wide, in another {B. signifer) it is 

 nearly globose. In the male of this last-named species, although the palpi are 

 as long as the proboscis, the last joint is similar in character to that of the 

 female. 



In the males of most species of A'edes and of Culex the palpi are longer than 

 the proboscis, curved upward, their outer halves densely hairy, the last joint 

 long and tapering. In certain species of A'edes the palpi of the male are slightly 

 shorter than the proboscis, straight, less hairy, the last joint long but blunt at 

 the tip. In A'edes fuscus the palpi of the male are very short, in fact shorter 

 than those of the female, and the terminal joint is indicated by a flattened 

 tubercle. In the related genus Stegoconops the reduction of the male palpi has 

 become more general. In S. equinus the palpi of the male are about three- 

 fourths the length of the proboscis ; in S. alhomaculatus the palpi are practically 

 alike in the two sexes, short and with a minute terminal joint. 

 5 



