46 MOSQUITOES or NORTH AMERICA 



He considers that, of the three metameres bearing the mouth-organs in typical 

 insects, the first metamere forms, above, united with the epipharynx, the labrum, 

 which he calls "scutum dorsale " (of the first metamere), and below in large 

 part the labium, which he calls "scutum ventrale" (of the first metamere). 

 The second metamere, according to Meinert, in the Diptera, bears the two pairs 

 of appendages usually called mandibles and maxillse and which he calls respect- 

 ively cultelli and scalpella. He does not consider these appendages homologous 

 with the mouth-parts of other insects on the one hand, or with the limbs of the 

 body on the other. He believes them processes or evaginations of the plates of 

 the second metamere ; the scalpella as processes of the ventral plate, the cultelli 

 as processes of the pleural plates. The palpi are in his opinion homologous with 

 the entire maxillse of other insects. This last conclusion appears particularly 

 interesting as Kellogg has found, in his study of the development of another 

 nemocerous fly, Bibiocepliala, that the palpi of the imago develop inside the 

 maxUlffi of the larva. The clypeus is designated by Meinert the " scutum 

 dorsale " of the second metamere. The third metamere, the one bearing the 

 mandibles in biting insects, is stated to be without appendages. More recent 

 investigations have shown that it is impossible to trace the primitive metameres 

 in the organization of the head of the fully developed insect. 



In view of the differences in opinion in the interpretations of the dipterous 

 mouthparts, and the impossibility of settling this question definitely by compar- 

 ative studies, Kellogg took up the study of the development of the imaginal 

 mouthparts witliin the larva. The larvae of the more primitive Diptera are the 

 essential ones in such an investigation, as they have a complete head and mouth- 

 parts corresponding with the typical ones of mandibulate insects. Kellogg 

 studied forms with such larvas. His investigations were made with Simulium 

 and BihiocepJiala, two Nemocera which, like Culex, have a complete set of 

 mouthparts in the female. We quote the important part of Kellogg^s paper : 



"... Can the homologies of the dipterous mouth parts be discovered by the 

 study of the development of the parts ? 



" For a complete developmental study of the mouth parts of any dipteron it 

 would be necessary to begin with the budding appendages of the head segments 

 in early embryonic life, to trace the development of these appendages to their 

 definitive form in the hatched larva, and finally to follow the transformation, if 

 it occurs, of these larval parts into the ultimate imaginal ones. As a matter of 

 fact, such actual transformation does not occur, so that the study of the post- 

 embryonic development of the mouth parts consists of noting the ecdysis of the 

 larval parts and determining the ontogenic relations of the new imaginal parts 

 to the old larval ones. 



"As for the embryonic development of the mouth parts — i. e., the development 

 from budding appendages to definitive larval parts, that has been done foi 

 several Diptera, and in particular by Metschnikov for Simulium, one of the two 

 flies whose postembryonic development I shall describe. These embryonic 

 studies make certain the homologies of the larval parts; in those flies like 

 Simulium, whose larvae are provided with a biting mouth with full complement 

 of parts, it is easy to note plainly the development of mandibles, maxillas, and 

 labium from the successive pairs of budding head appendages, and thus to 

 homologize these parts certainly with the mandibles, maxillse, and labium of 



