582 MODERN CLASSIFICATION OF INSECTS. 
In the inner part of the head, between the roots of the antenne, 
arises an elongated fleshy lobe, which, when in action, is folded back, 
extending quite to the hinder extremity of the cavity of the head, and 
capable of protrusion, having at its extremity, but placed so as to 
point forwards, along curved, horny, slender, and nearly tubular seta, 
channeled along its upper edge, and dilated at its base, receiving in its 
upper channel two other seta* of unequal thickness, but of equal length 
(fig. 133. 8.). The apex of these three seta passes through the mi- 
nute orifice above mentioned (fig. 133. 7.), and when at rest is to 
be observed sheathed between the two coriaceous valve-like plates ; 
but when in action the internal lobe is pushed forward, and the sete 
are conjointly porrected (passing through the minute orifice like a 
thread through the eye of aneedle), their basal portion extending as 
far as the base of the rostriform plates. It is exceedingly difficult to 
trace the analogies presented by these various organs.+ 
The three internal sete being of unequal size, and consequently 
single organs, cannot represent either mandibles or maxille, and 
must therefore be regarded as the analogies of the Jabrum, lingua, and 
labium; the mentum must therefore be the base of the latter, and 
cannot be regarded as represented by the membranous plate covering 
the front of the underside of the head, as described by Mr. Curtis. 
What then are the two rostriform plates? these being double must 
represent either mandibles, maxilla (as doubtingly described by 
Curtis, Dugés, and Newport), maxillary palpi, as supposed by La- 
treille, or labial palpi or labial lobes, as regarded by Dufour. The 
two latter analogies would be negatived by the existence of a distinct 
and separate internal labium. They can scarcely be maxillary palpi, 
because the maxillee are not developed, whilst their situation, arising 
from the underside of the head, seems to imply, regard being had to 
the other parts of the mouth, that they cannot represent either man- 
dibles { or maxilla. Moreover there are only a single pair of these 
* Latreille states this instrument to be composed of two sete, and Dugés of four. 
I have only found it to consist of three, as has also Curtis. 
+ Dugés (in his Memoir on Pulex), Curtis, Newport (art. Insect, in Cycl. Ana- 
tomy), and Percheron (Gen. des Ins. Dipt. pl. 6.) have attempted to trace these 
analogies, and have arrived at various conclusions. 
+ That they are not mandibles, seems to result from the non-development of 
maxillz, the latter existing in all Diptera which possess the former. Latreille has 
observed that “ dans les Melophages la base des lames du sugoir est recouverte par 
deux petites piéces coriaces, triangulaires, réunies, et formant une sorte de labre. 
Elles semblent representer, en petit, les deux piéces qui recouvrent la base de la 
