Article beginning on page 363.
Psyche 8:363-365, 1897.

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THE MOUTHPARTS OF THE NEMATOCEROUS DIPTERA, V. BY VERNON 1.. KELLOGG, STANFORD UNIVERSITY. Having examined the mouth struc-
ture of representatives of all (except
one) of the families of Nematocerous
Diptera we are in position to state in gen- eral and inclusive terms the characters
of the mouthparts of the Nematocera.
The mouthparts are composed of
(retaining the nomenclature hereto-
fore used) a labrum-epipharynx, a pair
of mandibles, wanting in the males of
all families, and wanting in both sexes
of a few families, a pair of maxillae,
in which never more than one terminal
lobe is present, and this failing in a few instances, and a labium, whose palpi
are totally lost, and whose terminal
lobes show a considerable range in
degree of coalescence. The condition
of the various parts may be described in more detail as follows :
The labrum-epipharynx is always
present and always free; it is
longer
than broad, pointed though not always
sharply, and, as seen from above, well-
chitinized. It is composed of two
Iamellae (often separable by dissec-
tion, or by treatment with potassium
or sodium hydrate) of which the upper
or dorsal one is a well chitinized
sclerite and is the labrnm s. sir. The
lower or ventral one is a thin membran-
ous structure, often projecting slightly beyond the labrum and in almost all
cases bearing few or numerous taste
pits (?) and papillar sense (?) hairs.
The mandibles are, when present,
possessed only by the females; they
are wanting in both sexes in six of
the eleven families studied. The man-
dibles in the five families possessing
them are always free and distinct but
show very obviously their tendency
toward reduction and disappearance.
In their best developed and certainly
effectively functional condition, they
are long, slender, well-chitinized and
armed with, a fine but conspicuous den-
tation along- their inner margin. From
this condition they descend by quick
steps to the condition of small thin
weakly-chitinized delicate plates, practi- cally functionless.




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364 PSYCHE. [June-itgo.
The maxillae are always free except
at their very base: they possess a
basal sclerite, never separable into
cardo and stipes, a palpus always well-
developed and 4 or s-segmented, and a
single maxillar lobe, which is wanting
in a few cases. When present, this
lobe is a slender, elongate, weakly-
chitinized, thin, flat, process, with
pointed and " fringed " apex. It shows
gradual degrees of reduction to total
disappearance.
The labium is a frce, short (but little
longer than broad) under lip, with
basal sclei-ite only rarely showing
indications of its composition of two
parts (sub-menturn and mentum) and
with terminal lobes showing various
degrees 01 coalescence with each other.
The base of the labium is in some
instances united by membranes with
the bases of the maxillae. Palpi are
always wanting ; no unmistakable indi-
cations of them are to be found, al-
though in two forms examined, what
may be palpar rudiments are present.
The terminal lobes in freest condition
consist of the two free paraglossae
sometimes apparently 2-segmented, and
a median, always delicate, membranous
lobe representing the fused glossae.
The paraglossae when free, as is the
condition in almost all the Nematocera,
show no indications of pseudo-tracheae
and are rather thick, concave on their
inner faces, and more or less thickly
beset with hairs of varying size and
strength. In one family the paraglossae
tend to coalesce, and within the limits
of this one family (the Tipulidae) the
paraglossae may be found frce, partly
coalesced and coalesced almost com-
pletely. With the beginning of coales-
cence, appears the first indications of
pseudo-tracheae, and in the nearly com-
pletely coalesced condition, the system
of pseudo-tracheae is well developed.
The liypopharynx is probably always
present (in one or two instances I have
been unable to dissect it out satisfac-
torily on account of its minute size and delicacy). It is a delicate, membra-
nous, elongate, pointed plate, in which
the course and opening of the salivary
duct can usually be seen. It is always
frec from its base, arising from the
inner (upper) wall of the lahium to its
tip.
The homologies of the various mouth-
parts within the group Nematocera
seem obvious and certain. The differ-
ences between the mouthparts of Blepha-
rocera, Simulium, and Ceratopogon in
which mandibles and a functional maxil-
lar lobe are present, and the mouth-
parts of Bibio and Tipula in which there are no mandibles and no maxillar lobe is simply one of degree of specialization
by reduction. Similarly the single,
broad lobe with elaborate system of
pseudo-tracheae which constitutes the
labium oE Tipula simply presents the
extreme degree of coalescence (as
reached among the Nematocera) of
the outer terminal labial lobes, the para-



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glossae, which in Simulium, Rhyphus,
Dixa, and even in Symplecta (a Tipu-
lid) are free and distinct, and without
sign of pseudo-tracheae. The gradual
coalescence of paraglossae is seen
plainly in Mycetophila and among the
Tipulids, and the gradual appearance
of the pseudo-tracheae can be readily
traced in the Tipulid family. The gen-
eral tendency of specialization of the
mouthparts of the Nematocera is toward
the reduction and loss of the mandibles
and maxillae, and toward the special
development of the labium to be a
rasping, lapping organ, all-important in food taking. The physiological change
in food habit from blood-taking or sap
sucking, which demands piercing and
elongate sucking parts, to the lapping
of exposed liquids or the taking of solid food in small rasped-off particles mixed with a salivary or other secreted fluid, has been accompanied by the general
structural change already indicated.
Now, is the highly specialized mouth
of the Muscidae and other similar Bra-
chycerous Diptera reducible to the Ne-
matocerous mouth ? Can the parts of
the mouth of Musca be homologized
with the parts of the Nematoceious
mouth ? To display the evidence which
the comparative anatomy of the month-
parts presents touching the point will
require another paper. It is necessary
to present the gradations between the
most specialized of the Nematocerous
mouths, say that of Tipula, and the
mouth of Musca. I may only say here
the Dipterous mouthparts this will not
be taken to be a very difficult matter.
Finally, can the Nematocerous mouth
be reduced to the orthopterous, biting
type of mouth ? Are the so-called man-
dibles, maxillae and labium of Blepha-
rocera or Ceratopogon homologous with
the mandibles, maxillae and labium of a
cockroach ? Unfortunately there is no
persistent racial genus of flies with
orthopterous mouthpaits, like Eriocc-
phala among the Lepidoptcra. The
persistence of Eriocephala enables the
development of the highly specialized
mouth stiucturc of the butterfly to be
traced backward through the higher
moths, tluough the Tineids, and finally
through Eriocephala directly to the
orthopterous type. Comparative anat-
omy can here unaided satisfactorily
reveal the homologies.
But with the Diptera the most gen-
eralized mouth is far from the orthop-
terous type. And yet it seems not
unreasonable, nor violently imaginative
to see in the mouth of Blepharocera,
the modified but still recognizable man- dibulate mouth. However, a study of
the development, the ontogeny of the
mouthparts of some Nematocerous form
is necessary to present the needed con-
firmation of this supposition, and this
testimony of the ontogeny I hope to
present in some future paper.
As said at the beginning of these
notes, the scope of this paper is limited to the study of the comparative anatomy
of the mouthparts of the Nematocerous
June 1809.1 PSYCHE. 365
that to any one at all acquainted with
Diptera.




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