George Dimmock.

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

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The few diptera whose mouth-parts have been the object of the anatom-
ical studies, the results of which are noted in the following pages, were
chosen, on the one hand, with especial reference to their presenting a series
beginning with a species possessing 'simple, separate and fully developed mouth-
parts, and ending with a species of which the complexity of the mouth-parts
was due to coalescence and incomplete development of their different elements,
and, on the other hand, with partial reference to forms whose mouth-parts were
of sufficient length to render their study by sections, made with the microtome,
of value in determining their relative lengths, their positions and their attach-
ments. With the above-mentioned objects in view species of the genera Cule.r,
Bomhylim^ Eristalis, and Mmca were chosen. Upon the anatomy of the mouth-
parts of Culex the following notes probably add most to what has been previously
recorded. No study of the development of the mouth-parts has been made in
preparing the following paper; the results are anatomical only.

The work necessary for the preparation of this paper was done by me,
as student, in the Laboratory of the Zoological Institute in Leipzig^ and I gladly
take this opportunity of expressing my sincerest thanks to its director, my
honored instructor. Professor Leuckart, for the advice and encouragement which
he has given me in my studies.


Until Pabkicius, in 1775, first called attention to the importance of the
mouth-parts in the classification of insects, little or no valuable progress had been
made in the study of their comparative anatomy. Observations on the anatomy
of the mouth-parts of single insects are to be found in the works of many
writers, previous to the above-mentioned date, but they can be best regarded as
forming only a part of the history of the anatomy of single insects, and, so far
as they treat of insects which are further discussed in this paper, they will be
mentioned later.


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Fabricius writes, in the preface of his Systenia entomologiae^ ^ after dis-
cussing the confusion which existed in the classification of insects at his time,
'* Therefore I will try a new method, choosing characters, both of classes and
of genera, from the mouth-parts. These parts truly offer sufficient and con-
stant characters and far more natural genera.'' * In his Phllosojyhia entom-
oloffica * (p. 37-52), where his ideas are further elaborated, one finds that
Fabricius divided the mouth-parts of insects into palpi, clypeus (now the labrum),
mandibulae, maxillae, galea, labium, lingua, rostrum, proboscis and haustellum.
The proboscis and haustellum, the parts which concern us most here, are somewhat
confused in Fabricius' classification. The proboscis, he writes (p. 38), is membran-
aceous and bilabiate; the haustellum is extended, chitinous, and without articu-
lations ; ** with the former is no mention of setae, with the latter, he adds, setae
differing in number. He writes (p. 49), *'*The proboscis, so peculiar to the
diptera, is not possessed by all of them," "^"^"^ and, on the next page he gives
Bombylius as without proboscis. Again he writes (p. 52), "The proboscis
differs from the haustellum in that the proboscis is always bilabiate, the
haustellum never," f and that, " The haustellum, being the characteristic of
the class, is always present in the diptera; the proboscis is often entirely
absent." tt Furthermore Fabricius wiites (p. 39), "In the diptera are
two palpi, a haustellum very often received in a proboscis, while mandibles,
maxillae, clypeus and labium are absent." ftt From the above quotations it is
clear that Fabricius meant by the proboscis what is now known to be, for the
most part, labium; by haustellum, following the derivation of the word, he meant
the true suction-tube, whether of one part, or made up of setae. The confusion
which arises in the Fabrician use of proboscis and haustellum is mainly due to
his failing to recognize, in his so-called "haustellum" of Cidex and Bomhylius,
parts which correspond to his "proboscis" in Mmca, Syrphm and other diptera.

' For full titles referred to by superior figures, see Literature at the end of this paper.

♦ *'Novam ideo viam tentabo, cbaracteres et classium et generum ex instrumentis

oibariis desumens. Praebent sane sufBcientes, praebent constantes et genera multo naturaliora."

•• "Proboscis membranacea, bilabiata" "Haustellum porrectum, corneum,


*♦♦ "Proboscis tantum Antliatis propria, nee omnia ilia ea gaudent."
•j- "Proboscis differt ab haustello, quod proboscis semper bilabiata, haustellum vero

ft "Haustellum, classis continens characterem, semper in Antliatis adest, proboscis
saepe omnino deest.**

fff "Palpi duo, haustellum saepius proboscide receptum, absque mandibulis, maxillis,
clypeo et labio in Antliatis/'

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Since Fabricius' time the terms proboscia and haustellum have been used somewhat
indefinitely. Gerstfeldt sought to explain (p. 13 of his dissertation'*) Fabrieius'
meaning, but seems to have failed in clearly comprehending the difference which
the latter intended to establish between proboscis and haustellum. In the course
of this paper proboscis will be used, in its generally accepted meaning at present,
as a designation for such of the mouth-parts of diptera, taken together, as form
their more or less flexible, shorter or longer, sucking apparatus.

According to J. V. Carus (Geschichte der Zoologie, p. 559) Fabricius also
divided the insects into sucking and chewing species, a classification followed later,
by Clair ville,* Lamarck, Gravenhorst, and many others.

Savuiny,* in J 816, took the next important step in advancing our knowledge
of the mouth-parts of insects, and showed that all the mouth-parts of insects
were reducible to the same plan, that is to the plan which they present in
chewing insects. Most of Savigny's work was done on lepidoptera, because the
lepidoptera were supposed to have mouth-parts farthest removed in structure from
those of chewing insects. Savigny says (p. 10-Jl), "I am convinced that, when
one shall have better examined the mouth of the insects properly speaking, that
is to say those with six feet and two antennae, one will find that, whatever
form it may assume, it is always essentially composed of the same elements.*' . . .
"One discovers that the organ is the same; the use alone is modified or
changed. See the constant plan of nature. Thus I think I can assert, from
this time on, that the mouth of the diptera is formed of the same parts as that
of the hymenoptera. But to prove this proposition it is necessary to commence
by explaining the organization of the mouth of the hymenoptera." * Savigny
says farther (p. 13-14), "The mouth of the hymenoptera is, then, composed of four
unpaired organs, without including the jaw or mentum; namely, the upper lip,
the epipharynx, the hypopharynx and the under lip ; and of two pairs of organs,
the mandibles and the maxillae. The same organs are all found, either separately
or simultaneously in the mouth of the diptera. The under lip exists almost
always; it constitutes the proboscis, properly speaking. The maxillae exist
likewise almost always; it is these organs which bear the palpi, so that the

* "Je suis convaincu que, lorsqu'on aura mieux examine la bouche des insectes propre-
ment dits, c'est-a-dire, k six pattes et k deux antennes, on trouvera que, quelque forme qu'elle
affecte, elle esttoujours essentiellement composee des memes elements." .... "On sail que
Torgane est le meme: Tusage seul est modifie oa change. Voil^ le plan constant de la
nature. Ainsi je crois pouvoir assurer des k present que la bouche des Dipteres est form^e
des memes parties que celle des Hym^nopteres. Mais pour demontrer cette proposition, il
faudrait commencer par exposer Porganisation de la bouche des Hymenopteres."


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diptera have two maxillary palpi and have no labial palpi. When the maxillae
are apparently absent, as in the flies properly speaking, they coalesce with the
under lip. The mandibles ^re found only in certain genera ; they are, for example,
very evident in the breeze -flies, where they have the form of two slender blades.
The hypopharynx and epipharynx are the bristle, or the two intervening bristles.
The upper lip is a bristle or broader scale which covers the others." *

Savigny did not stop with the reduction of the mouth-parts of all insects
to a common plan, a result which seemed fairly to complete the work begun by
Fabricius, but, in his second memoir, recognizing the resemblance between the
mouth-parts of hexapods and those of the remaining arthropods (which he terms
apiropods), and the graduated forms between the locomotory and manducatoiy
appendages of some of these apiropods, he concludes (p. 43) that, "among these
lask apiropods [by which he means TAmulm, Apm, etc.] the organs which serve
for manducation do not essentially diflfer from those which, among the first
apiropods [meaning lulus, Scolopendra, and the like], and among the hexapods,
serve for locomotion.'' ** Here was a direct homologizing of the mouth-parts of
insects with locomotory organs, a theory which Savigny had publicly advanced
as early as October 1814.*** The comparison of the paired appendages of
spiders, scolopendra, and Crustacea, which follows (p. 48-66 and 83-101) in his
memoir, has little interest in connection with the study of diptera.

After Savigny had thus led the way, by his theories that all mouth-parts
of insects were modifications of the same general plan, and that the paired mouth-
parts were serial homologs of legs, little was left in the way of general theories

* "VoiR done la bouche des Hymonopteres composee de quatre organes impaires,
sans y comprendre la ganache ou le menton; savoir: la levrc superieure, I'epipharynx,
rhypopharynx et la Icvre inferieure, et de deux organes paires, les mandibules et les
machoires. Les niemes organes se retrouvent tons, soit separement, soil simultanement, dans
la bouche des Dipteres. La levre inferieure existe presque toujours ; elle constitue la trompe
proprement dite. Les machoires existent de meme presque toujours: ce sont elles qui
portent les palpes, de sorte que les Dipteres ont deux palpes maxillaires, et n'ont point de
palpes labiaux. Quand les machoires semblent disparaitre, comme dans les Mouches pro-
prement dites, c'est qu'elles se confondent avec la levre inferieure. Les mandibules ne
s'observent que dans quelques genres: elles sont, par exemple, tres- visible dans les Taons,
oii elles ont la forme de deux lames tres-deliees. L'hypopharynx et I'epipharynx sont la
soie, ou les deux soies intermediaires. La levre superieure est une soie ou ecaille plus large
qui couvre les autres."

*♦ Chez ces demiers Apiropodes, les organes qui servent a la manducation ne dif-
ferent pas essentiellement de ceux qui, chez les premiers Apiropodes et chez les Hexapodes,
servent k la locomotion."

♦♦♦ See foot-note of p. 43 of Savigny's second memoir.

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which later investigators could advance, and we consequently find them confining
their attention to minor anatomical points, or to discussions of how many and
which of the mouth-parts are really homologs of legs, and to homologizing the
coxal, femoral, tibial, or tarsal parts of insects' legs with portions of their
mouth-parts. Savigny had already expressed his opinion (p. 41 of his second
memoir), that, besides the paired organs, the under lip "can be considered as
formed by the union of the two second maxillae/' *

Erichson, • in 1840 (p. 4-7 of his Entomographien)^ discusses the mouth-
parts of insects, devoting the greater part of his space to the consideration of
the under lip, which he regarded as originating in the union of a pair of organs,
in fact, speaking of it throughout his paper as the third pair of jaws. ** He
says (p. 4-5) "The third mandibular pair forms, in insects proper, a constant
part of the under lip, which is fonned by the union of this pair with the mentum
and with the tongue (ligula). This third pair has the mentum behind and
beneath, and the ligula above and before it, but is always characterized by
labial palpi which belong to it.'' *** He further adds (p. 7), " In the two
other orders of insects with sucking mouth-parts, the diptera and hemiptera, the
coalescence of the third pair extends still further upon the palpi, which form the
tubes of the proboscis, and sun'ound the remaining bristle-formed mouth-parts." f
In the male of Cuhw I have found, as will be more . fully described later, a
somewhat analogous case of union of the tongue with the labium; that is, ana-
logous, if one assumes the tongue, of Erichson, to be the hypopharynx, of Sa-
vigny, an assumption which may be incorrect, since Erichson fails to define clearly
what he means by tongue, or ligula. It is furthermore very probable that, as
Savigny stated, the labial palpi are absent in diptera, and I find nothing, in my
own observations, or in those of others so far as I have compared them, to show
that the proboscis of diptera is, in any way, the product of labial palpi. The
homologies found in Erichson's paper are of doubtful value, at least so far as

♦ *'Qu'on peut considerer comme forniee par la reunion des deux secondes machoires."'
♦* "pas dritte Kiefeq)aar."

*♦♦ "'Das dritte Kieferpaar macht hei den eigentlichen Insecten bestandig einen Theil
der Unterlippe aus, welche durch die Vcreinigung dcaselben mit dem Kinn {meniMni) und
der Zunge {ligula) gebildet wird. Dieses dritte Kiefcrj)aar hat nun das Einn hinter und
unter, und die Zunge iiber und vor sich, wird indess immer durch die ihm angehorenden
Lippentaster bemerkbar."

f "Bei den beiden andem Ordnungen der Insecten mit saugenden Mundtheilen, den
Dipteren und den Hemipteren, erstreckt sich das Verwachsen des dritten Kieferpaares noch
weitcr auf die Taster, welche die Rohre des Russels bilden, und die Ubrigen borstenformigen
Mundtheile umschliessen."

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they concern insects with sucking mouth-parts, because that, up to his time,
and indeed up to the present time, no sufficiently careful work has been done
on these parts to warrant such general conclusions as he pronounces.

The next important paper, in chronological order, upon the mouth-parts of
insects was by Brull^,' in 1844. I have not seen this paper, but I am able
to give a brief resume of the author's views, from the reviews of his paper
which appear in the dissertation by Gerstfeldt * (p. 5-9), in a paper by Menzbier **
(p. 18- J 9), and in Erichson's Berirht fiber die ictssenAchaftllchen TjeiMungen im
Gebiete der Entomologie (1844, p. 3-4). Savigny had regarded the labrum,
epipharynx, and hypopharynx, as unpaired organs. BruU^ sought to include these
three organs in the system of paired appendages, which Savigny had established
for the mandibles, maxillae and labium. Brulle considered the insect's head as
made up of six segments, each with a pair of appendages, or with an unpaired
appendage which owed its origin to the coalescence of a pair of appendages. The
first segment consequently bore the labrum, the second the epipharynx, the third
the hypopharynx, the fourth the mandibles, the fifth the maxillae, and the sixth
the labium.

Blanchard,® in 1850, considered that the most important modifications of
the mouth -parts of diptera were caused by coalescence of parts, and endeavored
to support his views by the origin of the nerves which go to these parts. In
the Asilldae, where only four setae are present, he regarded the mandibles as
present, but grown together to form what is now termed the hypopharynx. In
the Mmddae, and in other diptera with two setae, the mandibles were united
to form the hypopharynx, and the maxillae coalesced with the labium. The
above-expressed view that the so-called hypopharynx is composed of two mandibles
grown together, a theory followed in Cuvier's Regne Animal, does not seem so
improbable as it otherwise would in the light of Weismann's ^® statement (p. 190)
that, in the Muscidae '* The mandibular seta arises by coalescence of paired pieces,
which surround, like the two halves of a sheath, a cylindrical chain of cells which
tapers anteriorly. The cell-chain becomes the salivary duct, which in the imago
comes from behind to the under surface of the seta, so as to unite with it and
to open out a little behind its point with a fine opening." *

Gkrstpeldt/ in 1853, (p. 13-47) discusses the mouth-parts of diptera. After

• "Die Kieferborste entsteht durch Verwachsung paariger Stiicke, welche einen cylin-
drischen, nach vorn sich verjungenden Zellenstrang umschliessen, wie die zwei Halften eines
Futterals. Der Strang wird zum Ausfiihrungsgang der Speicbeldriisen, der in der Imago
von binten her an die untereFlache der Borate tritt, am mit ihr zu verwachsen und etwas
vor der Spitze mit feiner Oe£fnung auszumiinden."

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preliminary remarks on the nature, size, direction, and general form of the
proboscis, the author considers the parts and their nomenclature according to
previous authors. His compilation of authorities is very complete. In a few
words, the author's own views may be condensed as follows: The proboscis of
the diptera consists of a sheath and its enclosed setae, or bristles. The sheath
is made up, sometimes of the labium alone, sometimes of the labium as the chief
portion, together with other mouth-parts; it can be regarded as consisting of
three parts, the basis, the stem or stalk, and the end-lobes (labellae of Kirby).
The setae or bristles enclosed in the sheath represent the remaining mouth-parts,
and are either given as two, four, or six; or as one, three, or five; according
as whether one includes the labrum with them or not. The labrum is more or
less elongated, sometimes with a longitudinal furrow in the middle, supposed by
Gerstfeldt to be an indication that this mouth-part was composed originally of
lateral halves. The other setae, when they are all present, are the mandibles t
maxillae and hypopharynx. Parts of the mandibles or maxillae sometimes unite
with the labium to help form the sheath. The hypopharynx, or tongue, is absent
in very few diptera. The epipharynx perhaps exists in a few cases, according to
Gei*stfeldt (p. 21), altho he says he has nowhere seen it. At the basis of the
proboscis are regularly, if not invariably, two more or less developed palpi.
Following the portions of Gerstfeldt's paper, of which the proceeding is an abstract,
is a brief description of the mouth-parts, their mode of coalescence, and their
presence or absence, in different families and genera of the diptera, beginning with
diptera having two setae and ending with those having six.

Gerstfeldt's work was based, as is apparent from his introductory remarks
(p. 4-5), on the view of Brull^ that all the mouth-parts of insects were reducible
to the modification of six pairs of appendages, themselves serial homologs of the
thoracic ambulatory appendages. The theory seems to have been assumed at
the outset of the author's work, and, therefore, to have had too much influence
on the conclusions which Gerstfeldt drew from his otherwise, in general, accurate
observations, for Gerstfeldt examined a large variety of material in the preparation
of his paper, and examined it carefully, as far as the instruments at the disposal
of anatomists of his time would allow. His failure, however, to recognize the
epipharynx in diptera led him to make a curious mistake. He has described, as
Menzbier * correctly observes (p. 65), the epipharynx of Musca freed from the
labrum as the hypopharynx, and failed to discover the true hypopharynx. He
regarded the longitudinal "suture" (probably in reality the channel) of the
epipharynx (his hypopharynx), as an indication that the hypopharynx owes its
origin to the coalescence of paired organs. Another mistake which Gerstfeldt

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made in regard to the mandibles of Culea^ will receive notice later, in the
description of those parts.

Passing over a number of works, which dealt with the anatomy of single
species, or which had for their object the elucidation of the anatomy of special
organs, the next important discussion of the mouth-parts of diptera is by Menzbier.

Menzbier,^ in 1880, devotes the first twenty pages of his paper to a critical
historical synopsis of the works in which the mouth-parts of diptera have been
especially considered, and sixteen pages further to a critical historical summary
of the Jiterature which treats of the development of the chitin covering and
appendages of insects, and to the results of the studies of Weismann, Kunckel
d'Herculais, and others, upon the histoblasts, or imaginal disks. Succeeding the

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Online LibraryGeorge DimmockThe anatomy of the mouth-parts and of the sucking apparatus of some Diptera → online text (page 1 of 7)