52 MOSQUITOES OF NORTH AMERICA 



quitoes in which either one or both of the two supposed basal joints are differ- 

 entiated in such a manner that they may be called true joints. We doubt that 

 these correspond to the two basal joints of the four-jointed palpus of the more 

 primitive Chaoborus; the integument is of the same character throughout, 

 simply that there is less chitinization at the " joints." Furthermore, it does not 

 seem plausible that joints would tend to disappear at the very point where they 

 would be most in use and most needed. 



Should we accept the two basal modifications as true joints, we would then 

 have, in the female Anopheles, which has in addition three well-defined joints, 

 mosquitoes with six-jointed palpi. If, on the other hand, we carry out strictly 

 the idea that these basal joints are secondary modifications, we must consider 

 all that part of the palpus below the first true joint as a prolongation of the 

 basal structure and a part of the maxilla itself. Thus we would have to con- 

 sider the first " long joint " of Anopheles, there being no jointing apparent at the 

 base of the palpus, as belonging to the basal structure. The palpi of Anopheles 

 would then be three-jointed in the female, two-jointed in the male. In the 

 normal Culex pipiens there would be but a single true palpal joint in the female, 

 two in the male. In the higher forms, where there has been a reduction to a 

 club-shaped organ, this appears to have been produced, not by fusion of the 

 joints, but by their loss. This unjointed club would then represent the basal 

 structure. 



This process of reduction, first in the length of the joints, then in their num- 

 ber, can in fact be traced progressively through the genera and species of mos- 

 quitoes. The arrangement we have adopted in our classification, although it was 

 founded upon other characters without reference to the palpi, follows very closely 

 this process in the two tribes. It is interesting to note that this reduction has 

 been the most rapid in the female, where the functions of the mouth-organs are 

 of the most importance, and that in the majority of species the palpi of the male 

 show the more primitive condition. Thus Anopheles, in which the palpi are 

 long in both sexes and show several joints, is to be regarded as the most primitive 

 mosquito, while such forms as Uranotcenia and Sabethes, with greatly reduced 

 and unjointed palpi, must be considered highly specialized. 



We have already, on a previous page, called attention to the view of Meinert, 

 apparently supported by Kellogg's histological work, that the palpi of the 

 Diptera are not homologous with the maxillary palpi of other insects but are 

 rather modifications of the maxillae themselves. As this view has some bearing 

 on the interpretation of these organs and the number of joints, we quote Meinert 

 in part : 



"... The palpi are regarded by everybody as corresponding to the maxillary 

 palpi of the other insects ; but I shall here make some comments on this. The 

 maxillary palpi always originate from a maxillary trunk, which, through an 

 intermediate joint, the cardo, springs from the metamere. They are, in other 

 words, only the outer joints (corresponding to the foot?) of the exponent. In 

 the Diptera, on the other hand, the palpi originate directly from the metamere ; 

 and while in the several-jointed palpi the first joint might be regarded as a 

 modified cardo, and consequently the outer joints of the palpi as homologous 



