George Dimmock.

The anatomy of the mouth-parts and of the sucking apparatus of some Diptera online

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saves all confusion of parts by indicating, at first sight, what mouth-parts are
meant.

If one considers, in order, the different mouth-parts of diptera, they are as
follows:

The labrum-epipharynx is composed of the labrum above and the epipharynx
beneath, united at their margins by a delicate membrane, which is often infolded
(Bombylim). The labrum and epipharynx may be separable in caustic potash
(Mmca) or inseparable (Empis according to Menzbier). The epipharynx may be
absent, according to Menzbier (Sargm). At its base the labrum-epipharynx may
be united to the apical end of the fulcrum by a true joint (Mmca)^ or without
joint (Cities); the labrum is always continuous with the clypeus at the base, the
epipharynx always continuous with the upper wall of the pharynx. The labrum-

* "... 69 chitinizirte Fortsatze der Schlandwand sind.



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— 43 -

epipharynx may have a single point at its tip {Mmca, Bombylius) or may end,
apically, in several points (Culex, and probably all SyrpUdae). The labrum-epi-
pharynx usually forms a cover for the channel of the labium below, and may be
separable from the labium, at the will of the insect {Cxdex)^ or may remain always
tightly closed over the labium (Mused), The labrum-epipharynx is usually, second
to the labium, the largest mouth-part of a dipteron. Within it may contain
muscles and tracheal stems {Bombylius and Musca), The channel of the epi-
pharynx is never completely cylindrical, but is slightly open along its under side ;
a tube is formed by. the pressing of the hypopharynx upward against this open-
ing; through the tube thus formed the food is sucked up to the mouth.

The hypopharjmx is usually present in diptera (according to Menzbier absent
in Sargus\ and contains a tube, opening by a channel on its upper surface ; this
channel extends back, more or less, from the tip, and is the outlet for the salivary
secretion. The tip of the hypopharynx may be naked and used as a lance
(Haematopota, according to Menzbier), or may be hairy (Mused). The upper side
of the base of the hypopharynx is continuous with the lower wall of the pharynx;
its under surface may entirely coalesce with the labium (Cvlex, male), may join
the labium more or less anterior to the mouth (Mvscd)^ or, if either mandibles or
maxillae are present, its base may join them (Culex, female).

The mandibles are the mouth-parts which are least developed, or most often
absent, in diptera. They are present in Cvlex, female, and, according to Menzbier,
in Haematopota ; they are absent in Eristalis, Bombylius, Musca, and many other
diptera. When present they are usually delicately lamelliform.

The maxillae are, next to the mandibles, the oftenest absent in diptera; but
when both maxillae and mandibles are present (Culex, female), the maxillae are
more developed than are the mandibles. Maxillary palpi are usually, probably
always, present in diptera, usually joining the maxillae at the base; they are
from one-jointed (Bombylius, Eristalis, Mused) to five-jointed (species of Cvlex)^
are more or less hairy, and lay outsicle the proboscis, attached near or at the
mouth. The position of the maxillary palpi in Musca has evidently created much
confusion in the homology of the parts of the proboscis of these insects. Their
location on the membranous bridge between the two upper edges of the distal
end of the folcrum (in section, pi. 4, fig. 1, /^, mp) seems to have led Gerstfeldt '
to regard the fulcrum itself as chiefly made up of the maxillae. Grerstfeldt
described two processes extending back from the base of his hypopharynx (really
the epipharynx), and figured them as inside the frdcrum. These processes he
regarded as the basal portions, or "cardines," of the hypopharynx; a view which



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- 44 —

is necessarily incorrect because his hypopharynx was the real epipharynx separated
by caustic potash from the labrum. Lowne^^ (p. 43) mentions and figures these
processes which he terms "apod^mes," and, as he incorrectly supposed the
labrum-epipharynx, his operculum, to be made up of the labrum with a maxilla
coalesced on each side, he regards these " apod^mes " to be the basal portions of
the maxillae. Thus from incorrect premises Lowne arrived at what I consider
to be a correct conclusion, that is, that these processes are the basal portions of
undeveloped maxillae. Macloskie^* regarded these same chitinous rods as the *'great
tendons'' of the mandibles, and then added (p. 159) the impossible idea, " This will
make the operculum represent two united mandibles, probably enclosing the labrum."
Macloskie correctly says, however, of these "great tendons," that they are to
the right and left of the fulcrum, and that they are slightly articulated to the
operculum. Menzbier® writes (p. 65) of these same parts, in a very indeterminate
manner, that, "they are simple muscle-tendons, which were less developed in
Syrphusy and consequently not described by us." * That these processes really
are the remnants of the basal chitinous supports of the maxillae is very probable,
because they are the only chitin-rods which occupy the relative position that is
occupied by the corresponding parts in other diptera (compare pi. 4, fig. 1, /?^
X with pi. 1, figs. 9 and 15, nut and mp\ pi. 2, fig. 1, i-l\ x\ and pi. 3, fig. 1,
/-«', x)', because they are imbedded in a fold of the base of the labium;
because they are not firmly joined to the labrum, or to any other mouth-part;
and lastly, because the maxillary palpi, altho not joined to these processes, are
above their distal ends, a position they would scarcely reach if these chitinous
tendons belonged to the mandibles or labrum. The maxillary palpi of Mmca
are not joined to any firm supporting piece ; the bridge or band of chitin, seen
at their base in pi. 4, fig. 1, is only a slight corrugation (as can be seen by
the section represented in pi. 4, fig. 1, fi', c), which is probably due to the
hinderance to irregular folding, — which would be otherwise caused at that point
when the proboscis retracts, — by the presence of the palpi themselves. The
maxillary palpi of Mmca^ then, by some cause, are displaced from their basal
supports, which remain in their places, without maxillae or palpi, performing, by
the muscles attached to them, another function, that is, the lateral swinging of
the proboscis when the insect is feeding.

The labium of diptera, their most fully dev^ped mouth-part, and one that
is always present, joins the head below the other mouth-parts; its under wall

* ''Es sind einfach Muskelsehnen, die bei Syrphos weniger entwiokelt und deshalb von
was nichtjbeschrieben sind."



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16 continuous basally, sometimes with folding, into the under wall of the head.
The labium is usually somewhat fleshy, containing muscles and two longitudinal
tracheal stems, and is hollowed out along the upper side to form a trough for
containing other mouth-parts. At each side of the tip, the labium, probably in
all cases, has more or less developed labellae, on the inner surface of which are
usually the channels termed pseudotracheae. These pseudotracheae may be absent,
however, as in Cttleo', The labellae are fleshy in Musca, less so in Eristalis, and
least so in Bombylius and Culex, While the labium of all insects is undoubtedly
the product of a coalesced pair of appendages, as Savigny supposed, and its parts
can be still further safely homologized, in many insects, with particular portions
of the maxillae, and altho it has been divided in Orthoptera and some other
insects into submentum, meutum, glossa, etc., I do not believe, that in the
diptera, our knowledge of the structure of the labium suffices for us to enter
safely on homologies of its parts, and I have, consequently, refrained from doing
so in the preceeding pages.

The mode of separation and approximation of the labellae is somewhat diffe-
rent in different diptera, and is, perhaps, worthy of a comparative notice in this
place. As already mentioned (p. 18), the labellae of Culex are attached to
the tip of the labium by a true joint, and have, each, a flexor and extensor
muscle. The labellae of Bomhylius, described briefly on p. 25, altho not
connected to the labium by a true joint, have each a flexor and extensor
muscle. When, however, one examines, by sections, the labellae of Eristalis,
which I have briefly described on p. 30, one finds only an extensor muscle
in each labella, and in the sections of the labellae of Mtisca one finds no muscles.
How, then, is the separation of the labellae effected in Mtisca, for both in Mmca
and in Eristalis their normal condition seems to be that of opposition ? Examining
the sections of the labellae of Eristalis (pi. 3, fig. 1, «') one sees that a chitinous
band passes through the middle of each labella, and that, to the outer side of
this band, the extensor muscle is attached. The bands serve as supports for the
labellae, and as attachments for their extensor muscles; and these bands are
themselves jointed at their bases to the inner or upper chitinous wall of the
labium. An examination of cross-sections of the labellae of Musca shows this
same chitinous band, but no muscle. The reason for the absence of the muscle
is that, as has been already described (p. 36), the muscle does not extend into
the cavity of each labella, but is only inserted on the base of these chitinous
bands. The labellae of both Musca and Eristalis are opened, then, at least in part,
by muscular force ; but probably the more complete separation of the two labellae
is caused by the same inflation with air, which, as previous writers have supposed,



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— 46 —

serves to protrude, and to press firmly, the inner sor&ces of the labellae, upon
any surface from which the insect wishes to scratch or dissolve substances for
food. That it is air, at least for the most part, , and not water, which expands
the inner surfaces of the labellae, is easily proved by pressing carefully the head
of a fly between the fingers until the proboscis is fully extended, and the labellae
fully inflated, then, putting the fly under water, and pricking with a needle
the inner surfaces of the labellae ; they will at once collapse, bubbles of air
escaping, at the same moment, from the opening made in their surfaces by
the needle.

The pseudotracheae on the inner surfaces of the labellae of Mvsca are
cylindrical channels, sunk, more or less deeply, into the surface of the labellae,
according to the amount that that surface is inflated, and they open on the surface
in zigzag slits. These channels are held open by partial rings, more strongly chitin-
ized than the rest of the membrane of the cylinder. As seen from above in Musca
domesticay the pseudotracheae (pi. 4, fig. 6, b) appear to be supported by partial
rings, one end of each of which is forked. Such a ring, if isolated, would appear
as in fig. 6, d. These rings are apparently arranged so that one has its fork
on one side of the opening of the channel, the next ring the fork on the opposite
side of the channel, and so on, in alternation. This, I say, is the apparent
structure, for if one expands the membrane of the inner surface of the labellae,
to a sufficient extent, the channels, or pseudotracheae, are flattened out and their
true structure is revealed. PL 4, fig. 7, represents a portion of such a flattened
out pseudotrachea of Musca domestica^ the structure of which is immediately
evident; at the right-hand side of the figure is represented an irregularity, such
as now and then occurs in pseudotracheae. If such a piece of flattened pseudo-
tracheae as is seen at the left, in fig. 7, be formed into a cylindrical channel,
its appearance will be as in pi. 4, fig. 6, b. In Musca vomitoria the pseudo-
tracheae have a structure somewhat different in detail, but not in principle, from
those already described, as can be seen from fig. 5 without further description.
The pseudotracheae of Eristalis horticola are so nearly like those of Musca
vomitoria, that I have not figured those of the former. PL 4, fig. 8 represents a
section through a portion of the inner surface of a labella of Musca vomitoria,
cut at right angles to the direction of the pseudotracheae which pass through it;
in this section the intrapseudotracheal spaces are represented as protruded beyond
the edges of the pseudotracheae themselves; this is the natural position of the
pseudotracheae in repose, but when the fly inflates his labellae in the process of
eating, the soft intrapseudotracheal membrane is stretched, and the margins of
the pseudotracheae are protruded beyond the general level of the surface of the



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— 47 —

labella. These margins of the pseadoiaracheae consist of the lobes, or teeth, to
be seen at each side in pi. 4, fig. 7. The ring-like structure of pseudotracheae
has the same function as the similar structure in the tracheae of insects, or in the
wind-pipe of vertebrates, that is the function of holding tubes open, and preventing
their sides falling in upon one another. The same peculiar ring-like structure
is also found, with like functions, in the salivary ducts of diptera. If the labellae
are now alternately inflated, a little more and then a little less, the width of
the zigzag openings of the pseudotracheae is alternately increased and diminished,
and the teeth along the margins of the cleft naturally scratch on the surface
on which the fly has pressed his labeUae. The same scratching effect is produced
when the labellae are simply moved a little back and forth upon any surface.
The labellae are, then, files of which the teeth are the serrate edges of the
pseudotracheae. During the scratching process the pseudotracheae are, in Musca^
moistened with saliva, with which they wash the surfaces of the substance to be
scratched or dissolved away. Lowne** says of the pseudotracheae (p. 47-48)
''these form a fine strainer through which the insect is enabled to filter the fluid
from the solid portion of the substances on which it feeds." In Bombylius —
which offers excellent facilities for studying the pseudotracheae, because they,
altho constructed on the same principles as, are more firm and consistent
than, in Mttsca, — I have found that, after feeding the fly with a mixture
of sugar and gum-arabic, * colored with carmine, and then plunging it
suddenly into strong alcohol to fix the colored solution in its mouth-
parts, that, later, when I cut sections of its labellae, the pseudotracheal teeth,
instead of having their ordinary position (see pi. 2, fig. 5, a ; in section, fig. 6.
a), were turned outward from the pseudotracheal channel, into the position seen
in pL 2, figs. 5 and 6, b, and that the colored solution of gum-arabic had not
entered the pseudotracheae. Bombylim also rubs the labeUae over the surface
of the substance on which it is feeding, in a way similar to that which Mmca
does. It can be seen that the more purely liquid food any species of diptera
eat, for a constant diet, the less necessary and the less developed are the
pseudotracheae; CuUx, for example, eating a purely liquid food, has no pseudo-
tracheae. From the above fstcts, I am led to think that the primary function,
at least, of the pseudotracheae of diptera is to file away substances on which
they feed. That the pseudotracheae may have other functions, I do not wish to
af&rm or deny.

The pharyngeal sucking organs of the four different genera of diptera which
I have studied have been so fully compared in the comparison of the fulcra in



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— 48 —

these genera, that I need not further refer to them. The oesophageal bulb, as
sucking apparatus, behind the oesophageal nerve-ring, exists, as far as I know,
only in Cvlex, and cannot therefore be compared with any oth^ like structure;
and I will here end my notes on the comparative structure of the mouth-
parts and suctorial apparatus of the diptera, whose examination and- dissection
furnished me the materials for this paper.



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LITEBATURE.



* Fabricius, Johann CbriBtian. Systema entomologiae, sistens insectomm classes, ordines,

genera, species adiectis synonymis, locis, desoriptionibos, observationibus. Flensborgi
et Lipsiae, 1775.

' M^hricius, J. C. Philosophia entomologioa sistens sdentiae fandamenta adiectis defini-
tionibus, exemplis, observationibus, adumbrationibus. Hamburgi et Kilonii, 1778.

* Oerslfddtf Georg. (Jeber die Mundtheile der saugenden Inseoten. Ein Beitrag zur ver-

gleiohenden Anatomie, welchen zur Erlangung der Magister-Wiirde . . . zu Dorpat.
Dorpat, 1858.

* ScheUenherg, Johann Rudolf. Helvetische Entomologie . . . Ziirich, 1798, 1806.

According to Hagen (Bibllotheca entomologica, I, p. 181 ; II, p. 120) this work was translated

into French by J. de Clairnlle and published, the same years, in German and French. Percheron

(Bibliographie entomologique, I, p. 68) cites only Clairyille as author. Gerstfeldt credits Clairyille
with hairing first divided insects into suckers and chewers.

^ Savigny, Jules Cesar. Memoires sur les animaux sans vertebres. Premiere partie . . .
Premier fascicule. Mem. 1-2. Theorie des organes de la bouche des Crustaces et
des Insectes. Insecta, Linn. . . . Paris, Janv. 1816.

* Erichson, Wilhelm Ferdinand. Entomographien, Untersuchungen in dem Gebiete der

Entomologie . . . l Ueber zoologische Charactere der Insecten, Arachniden und
Orustaceen. Berlin, 1840.

^ BmUS, Auguste. Becherches sur les transformations des appendices dans les Articules.
(Ann. des sciences natur., 1844, ser. 3, t. 2, p. 271-374, tab. 1.)

* Menzbier, Michael Alexander. Uber das Kopfskelet und die Mundwerkzeuge der Zwei-

fliigler. (Bull. Soc. imper. natur. de Mosoou, 1880, t. 55, no. 1, p. 8-7 J, tab. 2-3.)

* Blanchard, il^mile. De la composition de la bouche dans les insectes de I'ordre des

Dipteres. (Compt. rend., 1850, t. 31, p. 424-427.)

I am dependent, for the contents of this paper on Qerstfeldt (p. 20), Henzbier (p. 19-20), and
Schaum's Bericht Uber die wissenschaftlichen Leistungen im Gebiete der Entomologie (1850, p. 100).

** Weismantif August. Die Entwicklung der Dipteren. ... l i)ie Entwicklung der
Dipteren im EL n. Die nachembryonale Entwicklung der Musciden. [Abdruck aus
der Zeitschrift fur wissenschafbliche Zoologie. xiii. und xiv. Band.] Leipzig, 1864.

4



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*^ Sivamfnerdamm, Johann. Bach der Natur . . . Leipzigi 1752.

In all cases where I haye had occasion to cite 8wammerdamm*8 Byhel der Natuure I haye
cited the aboye German translation.

*• Biaumur, R. A. F. Memoires pour servir a Thistoire des insectes.

Citations are giyen in this paper from the edition of this work published in Amsterdam, 1787-1748.

^' Earth, Johann Mathaeus. Dissertatio de colice. Ratisbonae, 1737.
I have not seen this work.

** Sulzer, Johann Heinrich. Die Kennzeichen der Insekten . . . Ziirich, 1761.

** Gravenhorst, J. L. C. Gmndziige der systematischen Natorgeschichte . . . Breslau, 1817.

^* Meigen, Johann Wilhelm. Systematische Beschreibung der bekannten europaischen zwei-
fliigeligen Insekten . . . Aachen, 1818-1838.

^' Packard, Alpheas Spring, Jr. Qnide to the study of insects . . . Salem, 1869.
Citations are from the first edition.

** Jordens, Johann Heinrich. Entomologie und Helminthologie des menschlichen Korpers . . .
Hof, 1801.

*• Claus, Carl. Grundziige der Zoologie . . . Marburg und Leipzig, 1876.

** Boffredri, D. Moriz. Memoire sur la trompe du cousin et eur celle du taon . . . (Miscell.
Soc. Taurinens., 1766-1769, t 4, p. 1-46, tab. 3.)
I haye not seen this paper.

?* Suffolk, W, T. On the proboscis of the blow-fly. (Monthly microscopical Joum.,
June 1869, v. 1.)
I have not seen this paper.

•• Gleichen, Friedrich Wilhelm. Gesohichte der gemeinen Stubenfliege . . . Niimberg, 1764.

'• Loume, Benjamin Thompson. The anatomy and physiology of the blow-fly (Musca
vomitoria, Linn.) . . . London, 1870.

** Macloskie, George. The proboscis of the house-fly. (Amer. Naturalist, March 1880,
V. 14, p. 153-161, fig. 1-3.



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VITA. .

The only child of George Monroe, and Elizabeth Learned Dimmock, I, Oeorge Dimmock,
was bom the 17th of May 1852, in Springfield, Massachusetts, U. S. A.

After several years of study in the public schools of my native city, I was fitted, at
the Harvard School, a private school in Springfield, to enter Harvard College, Cambridge,
Massachusetts, which I entered in 1873, and from which, on graduation in 1877, I received
the degree of bachelor of arts, with honors in natural history.

In October 1879, I was matriculated, as student Qf natural history, in the University
of Leipzig, where I remained until the autumn of 1881. In Leipzig my time was chiefly
devoted to the study of zoology in the laboratory of Professor Leuckart, in addition to
whose lectures, I attended lectures by Professors Carstanjen, Cams, Credner, Schenk and
Wiedemann, and by Doctors Chun, Fraisse, von Ihering, Luerssen and Marshall.



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EXPLANATIONS OP THE PLATES.



The following letters have the same signification on all the plates:

m, mandibles.



c, clypeus; &, its folds.

e, epipharynx.

/, fulcmm.

hf hypopharynx.

i, infraoesophageal ganglion.

I, labium; V, I", its folds.

lb, labellae.

Ir, labrum.

Ir-c, labmm- epipharynx.



mp, maxillary palpi.

mx, maxillae.

oCf oesophagus.

p, pharynx.

pm, pm', pharyngeal muscles.

8f supraoesophageal ganglion.

tr, tracheal stem.

X, basal support of maxillae.



The number of diameters enlargement is indicated against each figure.

Greek letters are used to indicate where sections are made in prolbosceSi
and the corresponding sections are indicated by the same letters, often with
an accent (').

Shaded parts of sections are portions filled with connective tissue,
nerves, air-spaces, and other parts having no significance in connection with
points discussed in the dissertation.



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EXPLANATIONS OP PLATE L



Fig. 1.— Side view of head of Culex rvfta, with extended mouth-parts;
a, antennae.

Fig. 2.— Same from above with mouth-parts partly cut away.

Fig. 3.— Tip of labium of female Culex.

Fig. 4. — Tip of labium of male CuLex,

Fig. 5.— Tips of separated setae of mouth-parts of Culex,

Fig. 6. — Tip of labrum-epipharynx seen from beneath and in section.

Fig. 7.— Cross-section through the labellae and tip of labium of female C%ilex,

Fig. 8. — Cross-section near the middle, of the proboscis of female Culex,

Fig. 9.— Cross-section through pharyngeal region of the forward part of the
head of female Culex,

Fig. 10.— Cross-section through the posterior part of the head of female
CWex, to show the sucking bulb of the oesophagus, h, lumen of
the oesophageal bulb, hm and hm'y muscles to dilate the bulb,
r, chitinous rods which support the oesophageal bulb, rmj retractor
muscles of the maxillae, at their point of origin, t, elastic plates of
sides of bulb.

Fig. 11. — Longitudinal section of the head of a female. Culex. b, oeso-
phageal bulb, gj point where the clypeus appears cut off firom the
rest of the head, v, valve between pharynx and oesophagus.

Fig. 12.— Cross-section near the middle of the proboscis of a male Culex,

Fig. 13.— Cross-section at the base of the proboscis of a male Culex.

Fig. 14. — Cross-section further into the base of the proboscis of a male Culex.

Fig. 15. — Cross-section through the pharyngeal region of the head of a male
Culex,



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EXPLANATIONS OP PLATE H.



Fig. 1.— Side view of the head of Bombylius major with its proboscis; at the
upper right-hand comer are figured the tips of the labram-epipharynx,
hypopharynx and maxilla, to illustrate their comparative sizes and
lengths. Below (a— A') is a series of cross-sections of various parts
of the proboscis and its base.

Pig. 2. — View of the head oi B, major from above, to show how the labellae
open.

Fig. 3.— Longitudinal section of the head of B, major, z, location where the
ventral posterior process of the fulcrum lays, d, location of the
dorsal posterior process of the fulcrum.

Fig. 4.— Tip of maxilla of B, major.

Fig. 5. — Perspective view of the chitinous portions of the pseudotracheae of


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