OF THE MOUTH TAllTS OF CERTAIN IXSECTS. 183 



tion. First let me say that I have ah'eady shown that a cliange from tkxil)le to rigid 

 hguhi is not uncommon, and the suggested union of the palpi is a much less violent 

 requirement than that imposed b\- the current explanation of the Dipterous mouth. 

 Referring for a moment to PI. I, Fig. 3, we see the entire mouth structure of Eristalis 

 tenctx. Above is the meutiun and submentum, very like the structure already de- 

 scribed for PoUstes and entirely homologous Avith it, and at its tip we find arising in a 

 group the structures further enlarged at PL III, Fig. 5. Centrally we find the now- 

 rigid ligula, deeply grooved in the middle, the channel closed by a flattened, also rigid 

 and chitinized hypopharynx. Loosely enveloping this central ligula is a more mem- 

 branous cylinder, evidently made up of two lateral halves, two-jointed, and the ter- 

 minal joints separated or paired except at the base. As in Bomlms the month of Eris- 

 talis is hinged, and the joint is also at the base of the ligula. The latter organ is .so 

 articulated as to allow of the flexion; but in the palpi we find again the [n'ovision 

 already noted in Bombu>< — a flexible, membranous, pseudo-segment. Now if we sec- 

 tion the Bomhus and M'istalts at the middle, we find the cuts alike, except that in 

 Eristalis the palpi are completely united over the hypopharynx and closely approxi- 

 mated at the opposite side. If we section near the tip, the cuts in both cases arc 

 identical. That this united structure in Eristalis is the united labial palpi seems to 

 me beyond doubt. In the first place, the point of origin is normal, next to the ligula 

 and at the tip of the mentum ; and, secondly, it is a jointed organ and therefore can- 

 not be paraglossa. It is in all points the structure of Bomlms, with the terminal joints 

 lost and the two halves united for the greatest part of the distance. That tlie parts 

 named mentum and submentum are really such, is proved by the fact that the hypo- 

 pharynx, which is not in dispute, originates from and that the (esophagus originates 

 within it. 



In Bomhus fercidns the ligula is unusually developed and much longer than the 

 labial palpi, while the paraglossa- are wanting. In PI. J II, Fig. 12, is a camera lurida 

 sketch of the labial parts of a carefully mounted specimen. The structures here ai'C 

 exactly as normally held when at rest, and only the mentum is a little crushed by the 

 cover glass on the shallow cell. Xow chitinize this whole structure thoroughly, and 

 then compare with the drawing of Chri/sops viftatus (PI. Ill, Fig. 13) made in the 

 >amc way. The magnifications are dilferent, of course, the lioinhus being drawn at 

 short range with a foui-inch lens while the Chnjsopf^ Avas drawn at long range under a 

 one-inch objective. The object was to get the two of ap[)roximately the same size for 

 convenience of comparison. In the Tabanids the mouth parts are rigid and not flexed, 

 and no sort of joint or hinge is recpiired; hence the slructui-cs ai'e all rigidly united at 

 tlie base to the mentum. In Bomhus fervidaa the palpi arc reinforced by a heavier 



