George Dimmock.

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

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historical part of his paper, Menzbier details the results of his own investigations.
After enumerating the regions of the head, according to his ideas of its structure,
he explains (p. 53-06) the mouth-parts of Haematopota, St/rphm, Empis, Mmca
and Sargiis, these genera representing a series, in which the first has all the
typical mouth-parts of a chewing insect, and the last only the labrum, labium,
and maxillary palpi. Menzbier seems to have been the first to recognize the
usual intimate union of the labrum and epipharynx in diptera, where he finds
them often separable by maceration in caustic potash. The following tabulation
gives, at a glance, the more important points in Menzbier*s paper, in regard
to the mouth-parts of those diptera which he studied.



Haematopota \
and Chrysops. J



Labrum and
Epipharynx.



Separable in
caustic potash.



jHypopharynx



lamelliform



Mandibles. Maxillae.



Labium.



I



lamelliform ' »^*^"***'' ; niuscular.
on uppersur-j j with palpi.

face. I



Syrphus taeniatua.



do.



do.



i



do.



I



palpi only. ] do.



Empk livida.


Not separable in
caustic potash.


1

! do.


absent.


united to form

an unpaired

needle, with

palpi.


Bilobed
at tip.


Musca species,
Sarcophaga cartiaria
Stomoxya calcitrana.


. Separable in ^^
caustic potash.


do.


1
palpi only.


muscular.


Sargus nubecidosus.


Labrum present,
epipharynx absent.


absent.


do.


do.


fleshy.



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The fulcrum, which Gerstfeldt regarded as united maxillae, Menzbier considers
to be chitinized processes of the oesophagus.

That the maxillae are grown together in Emjyis livida, is, perhaps, an error.
My having no specimens of Empis prevented my proving this point. Gerstfeldt
writes (p. 31-32), '*Four setae — which always represent the maxillae, the upper
lip and the hypopharynx, while the mandibles are united with the sheath of the
proboscis — are found in the Empidae (in Empis the maxillae are also shorter
than the hypopharynx, but this exceeds the upper lip; all four setae are pointed
and homy)." *

After recording some of his observations on the development of the epipharynx
and hypopharynx, Menzbier closes with a summary of his conclusions, which
would he superfluous, if transcribed here.

With this short resume of the advances made in the study of the general
structure of the mouth-parts of insects, especially those of diptera, I will pass
on to the recording of results of my own observations on single genera, prefixing
to my own remarks, brief notices of the work done by others in the same direction.



ANATOMY OP THE MOUTH-PARTS OP CULEX.

From early times Cu/e.r has attracted the attention of mankind, but, until
about two centuries ago, little or no progress was made in the knowledge of the
inner structure of its mouth-parts.

SwAMMERDAMM, ^^ who studiod Cukx in 1668, distinguished the male and
female, but evidently supposed that the structure of the proboscis of both sexes
was the same. He correctly distinguishes the long maxillary palpi of the males
from the short palpi of the females. He clearly recognized that there were six
mouth-parts enclosed in a sheath, but erroneously supposed them to be protrusile
from the end of the sheath, without flexion of the latter, and thus figured them.
The largest of these enclosed mouth-parts (really the combined labrum and
epipharynx) he supposed enclosed the other five, and he says (p. 147 of the
German edition of 1752), "I regard it that these five setae serve, like as many
sharp little awls to make the opening in the sweat-pores of the skin. When
this is done they draw themselves back again into the inner sheath. This then

* "Vier Borsten - die immer den Maxillen, der Oberlippe und dem hypopharynx ent-
sprechen, wahrend die Mandiblen mit der Riisselscheide verschmolzen sind — besitzen" . . .
"die Empiden (bei Empis sind die Maxillen ebenfalls kiirzer als der hypopharynx, dieser
iiberragt aber die Oberlippe; alle vier Borsten sind zugespitzt und homig).*' . • .



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enters (according to my idea) into the wound with its sharp cavity, and the
mosquito sucks through it the blood, which ascends alongside and between the
little setae into the belly of the mosquito/' * The apical opening of this inner
sheath he correctly thought to be turned toward the ventral side.

Leeuwenhokk next endeavored to settle the structure of the proboscis of
Cnlex. All that I know of his work is from what Reaumur'- (13** m^moire,
t 4, p. 401-40H) says of it. Leeuwenhoek found only four setae in the sheath
of the proboscis, and doubted that the inner sheath, described by Swammerdamro,
existed as a closed tube. Barth, ^^ on the other hand, in 1737, according to
Reaumur (1. c, p. 403); thought the inner sheath was a closed tube and not a
channel.

RftAUMUR, '* in 1738, published his description of the mouth-parts of Culex,
and of their mode of biting; to the latter subject he gave much attention, and
was the first to describe coiTectly how the sheath was disposed of during the
use of the setae within, in the act of biting. He also calls attention to the
poisonous effects of the bite, and, contrary to the views of Leeuwenhoek, who
thought the inflammation following the bite of Cule.r was due to the peculiar
nature of the wound itself, that is, that they were the natural consequences of a
wound made by an instrument of a particular form, Reaumur regarded the sub-
sequent inflammation of the place bitten by Cule.r to be due to a poisonous liquid
which the insect injects into the wound, in order to cause the blood to flow
faster. Reaumur found only five of the six setae which the proboscis contains.
He favored the idea that the inner sheath, which Swammerdamm had described,
was not cylindrical, but only a channel open on one side. Reaumur also arrived
at the idea that the maxillary palpi of Cule^r could, in some cases, help to form
the sheath which encloses the setae, but he does not clearly say that they always
do so in the males.

Since Reaumur's time but little has been added to our knowledge of the
mouth-parts of Ctdex, some writers following the statements of Swammerdamm,
others those of Reaumur, or of Leeuwenhoek, in regard to the number of setae.
Among others I will cite Sulzer ** (176J), who- says "four to five pointed tubules;"**

* "Ich halte davor, diese fiinf Angelgen dienen dazu, als niit so viel spitzigen Pfriem-
gen -die Oeffoung in den Schweisslochern der Haut zu machen. Wenn dass gethan, so
Ziehen sie sich wiederum in die innere Scheide zuriick. Diese dringt dann fnach meinem
Begriff) mit ihrer spitzigen Hohle in die Wunde hinein, und die Miicke saugt durch sie das
Blut in sich, das neben und zwischen den kleinen Angeln bin in den Bauch der Miicke
hinaufsteigt."

*♦ "4—5 spitzigen Rohrchen." (p. 169.)



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Fabricius ^ (1775), who writes, "sheath exserted, univalvular, flexible, . with five
setae;"* JOrdens^® (1801) describes four setae;** Gravenhorst** (1817), "The
proboscis long, setiform, five-parted;*** Meigen^^ (1818) describes four setae and
figures five;t Gerstfeldt ' (1853), "The sheath is formed of the under lip alone,
and contains six setae;" ft Packard^' (1869), "These six bristle-like organs are
folded together within the hollowed labium;" ftt Claus^* (1876) writes, proboscis
"extended with four setae." §

RoFPBBDRi's paper, **^ in 1769, upon the mouth-parts of Cule,c, I know only
by title.

Without being unduly influenced by one or another of the authorities above
mentioned, I will set forth the structure of the mouth-parts of Culejc, both male
and female, as I have found them in my own observations, in the following pages.



THE MOUTH-PARTS OF CULEX, FEMALE.

The mouth-parts which form the proboscis of the female Culex, as I have
found them by study of C. rufm, C. ciliatus and C pipiens, represent all the
typical mouth-parts of different insects, and consist of a labrum (PL 1, fig. 1, /r.),
an epipharynx (e), a hypopharynx (A), two mandibles (m) and two maxillae (ma;),
all sheathed, when in repose, in the labium (/), which receives them into a groove
on its upper side. Each maxilla has a maxillary palpus {m p) which lies outside,
and at the base of, the labium; the latter has no palpi, unless one regards, as
Erichson did, the lobes at its tip to be palpi. Of these mouth-parts the labium
and maxillary palpi are covered with hair and scales, the others are naked, light
brown, setiform and transparent; they all originate at the anterior basal portion
of the head, below the eyes and antennae (a), and are, with the exception of the
maxillary palpi, of about equal lengths, that is, about three to four times the
length of the head. The maxillary palpi, in the females of Cuk^r proper, are
about the length of the head. Those mouth-parts which are without scales, and

♦ "Vagina exserta, univalvis, flexilis, setis quinque/' (p. 799.)
♦* P. 162, of Band L

•♦♦ '*Der Russel lang, borstenformig, funftheilig." (p. 44.)
t P. 2 and pi. 1 of Theil I.

ff "Die Scheide wird von der Unterlippe allein gebildet und enthalt sechs Borsten,"
(p. 32.)

ttt P. 369-370.

$ ** Vorgestreckt mit 4 Stechborsten," (p. 682.)



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these are the ones that penetrate the skin in biting, are not jointed; the labium
of the female Culex is not jointed throughout its length, but the lobes, or
labellae (Fig. 3 and 4, lb), are jointed to it, by a true joint, near its tip; the
maxillary palpi are sometimes four-jointed, sometimes five-jointed, probably varying
according to the species. Unlike the mouth-parts of most diptera, those of
Cvlex, with one exception, are free to the base ; this exception is that the labrum
and epipharynx are united their whole length, forming a piece, which is shown
in section in fig. 6, d. The labium and palpi are the only mouth-parts which
contain muscles. The epipharynx forms the channel through which Cxdex sucks
up blood; the hypopharynx probably furnishes a channel for the discharge of a
saliva-like fluid. A pumping organ, trianguloid in cross-section (fig. 10, h), for
sucking up blood into the pharynx, is formed by a dilation of the oesophagus
behind the oesophageal nerve-ring. Each of the above parts will be described
more in detail later. In comparative size and strength the mouth-parts would
be arranged as follows, the largest and stoutest first: labium, labrum-epipharynx
(the name by which I shall designate this compound piece), hypopharynx, maxillae,
and mandibles.

The general arrangement of the mouth-parts, relative to each other, is shown
best in fig. 8, which is of a cross-section through the middle of the proboscis
of a female Culex rufus, while in repose, with the setae sheathed in the labium.
The labium (/), clothed on the outer side with its scales and hairs, wraps itself
nearly around the other mouth-parts. In it lay the two maxillae {mx), partly
enclosing the parts above them, and thus helping to bind the parts together;
above the maxillae are the two mandibles (m), and immediately above the man-
dibles, in a median line, is the hj-popharynx (A), with a thickened middle
portion. Resting on the hypopharynx is the labrum-epipharynx {Ir and e)\
the epipharynx is omega-form in section, and above it, delicately attached, is
the labrum. The determination of the positions of ' the hypopharynx, mandibles
and maxillae, in a section, is difficult, because of their minuteness and
transparency, and because that they are very closely packed together, much
more closely, relatively, than they are represented in figure 8. Their
position was finally determined by the following process, which I repeated
several times to insure accuracy. The section of the proboscis, still in the par-
rafine in which it was cut, was put on a microscopic slide, covered with a
cover-glass, and a piece of blotting-paper laid at that side of the cover-glass
toward which the labium was turned. Then, while watching the parts carefully
with the microscope, turpentine was passed under the cover-glass, at the side
opposite the blotting paper, and allowed to flow slowly about the object until it



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was imbibed by the paper at the other side. Thus a constant stream of turpentine
flowed against the upper side of the mouth-parts, and they were dissolved away,
in the field of the microscope, one after the other, in the order, labrum-epi-
pharynx, hypopharynx, etc. The position of the parts can be also determined by
pressing the head of Cidejr laterally between a cover-glass and a slide; in
perhaps one case out of every twenty tried, the parts will arrange themselves as
they did in the specimen from which fig. 1 was drawn. The changes in position
which the mouth-parts of Cxdex undergo as they approach the head can be best
described in the subsequent description, in detail, of each separate part.

The labrum-epipharynx (figs. 1, 5, 6, 7-8; Ir and e) of Culex consists of the
thin labrum resting upon and fastened to the epipharynx; it tapers gradually
from base to apex. The epipharynx is omega-form, being a channel rather than a
tube, a tube being formed by the pressing of the hypopharynx upon its under
side. The tube thus formed is the channel through which the blood, which
Culeo' sucks, passes into the oesophagus. At its base or proximal end the
epipharynx is supported and moved by strong muscles having their insertions on
the upper side of its wings or lateral portions, and upon the upper side of its
tube. These muscles extend upward and posteriorly, and have their origin on
the inner surface of the clypeus. (See fig. 9 and 11.) These muscles (pm) by
their contraction, elevate, and perhaps slightly retract, the epipharynx, and the
labrum, to which they are also attached. These muscles probably aid in suction,
for, when the setae are all stuck firmly in the skin, the contraction of these,
muscles would only serve to raise the base of ihe epipharynx from that of the
hypopharynx; this action would tend to produce a vacuum between the two (see
fig. D), and thus cause the blood to be drawn up in the tube of the epipharynx.
The probability that these muscles aid in suction is augmented by the fact that
the corresponding muscles in other flies, which cannot raise their epipharynx so
freely from their other mouth-parts as is seen in fig. 1, these muscles are devoted
to suction; and further, that in the male Culex^ which does not possess — as
does the female — a pumping apparatus behind the oesophageal nerve-ring, these
muscles are the ones that must serve for suction. The section, represented in
fig. 9, was taken near the base of the clypeus; a few sections further on,
posteriorly, the channel for the passage of food turns upward and then backward
again, passing in its course a place (fig. 11, r) where its walls approximate
dorsally and ventrally. This narrowing of the walls is probably a valve to
prevent the return of fluids to the mouth during the pumping process. I term the
portion in which this sucking process is carried on, the portion of the tube which
is between the mouth (where the mouth-parts unite to form a closed tube), and



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this valve, the pharynx; posterior to this valve, oesopTiagus. These limitations
of the oesophageal region will be found convenient later, when I compare the
mouth-parts and the sucking pharynx of Ctde.j' with those of other dlptera.

The tip of the labrum-epipharynx seems to turn upward (fig. 1, Ir-e), altho
the opening is upon the ventral surface, as may be seen in fig. 6, ft, which
represents the ventral view of the tip of this part. The tip of the labrum-
epipharynx is comparable to a quill-pen with three tips near each other, the
middle one of these three tips being slightly shorter than the other two. The
two lateral portions of the epipharynx, as seen in section, when they near the
tip, lay themselves closely upon the sides of the tubular portion, passing upward
upon it, as seen in fig. 5, lr-e\ they thus serve to strengthen the two outer
points of the tip of the epipharynx, while] the labrum continues to a sharp point
at the tip, and, united with the upper surface of the epipharynx tube, forms the
middle point of the tip. The channel, or slit, along the under side of the epi-
pharynx, widena toward the tip, leaving thus an opening for the passage of fluids
into the tube of the epipharynx.

The labrum itself is a thin lanceolate lamella of chitin, concave along the
under side from the basal portion to the tip, and its concavity rests upon and
fits to the convexity of the tubular part of the epipharynx, to which it is so
lightly attached that they readily separate by application of caustic potash. The
outer edges of the labrum roll slightly inward toward the epipharynx along most
of its length. (See fig. 6, d,) At its base the labrum sends a chitinous support
beneath the clypeus, where it separates more from the epipharynx and has its
own muscles, indicating that the labrum has a degree of motion independent of the
epipharynx, a motion allowed, perhaps, by the elasticity of the connection between
the labrum and epipharynx. The muscles of the labrum (fig. 9, pm ') are inserted
upon the upper side of its base and have their origin on the inner surface of
the roof of the clypeus. These muscles are, at least in the females of Culeo'
rufus, divided into three portions in their upper part, as shown in fig. 9.

The hypopharynx of the female of Culea; is a linear, lanceolate, transparent
lamella of chitin, with a longitudinal rod through the middle, the nature of which
will be discussed later. At its base the hypopharynx forms the continuation of
the under wall of the pharynx. (See fig. 11, k) The hypopharynx is closely
pressed upon the under side of the epipharynx, completing the tube nearly formed
by the epipharynx. No muscles have their insertion on the base of the hypo-
pharynx. Its tip is simply lanceolate (fig. 5, A). In Culejc pipims and C. rufm
nothing further is visible (with a magnifying power of five hundred diameters),
in sections of the thicker middle portion of the hypopharynx, than a simple



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— 15 —

rod of cbitiii ; but, in C. ciliatus, a North American species of which the mouth-
parts are larger, this rod appeared to be tubular. Is it a rod or is it a tube?
Menzbier * writes (p. 25) that in diptera " neither the labrum nor the hj-popharynx
possesses a completed tube, but only a channel' ' "^ which leads into the salivary
duct. That Menzbier is incorrect in affirming that the hypopharynx has no
complete tube I have clearly proved in my observations on Bonibylius and
EriMalts; but the question still remains unsettled whether Cukx has any passage,
either tube or groove, through the hypopharynx. K^aumur'^ (tome 4, part 2,
p. 896) discusses the probability of a poisonous fluid being secreted by Cule,T, to
cause the blood to flow more readily when it bites, and since his time writers
have, on the one hand, accepted this statement, without proving the presence of
such a fluid or of the glands to secrete it, or they have, on the other hand,
denied the existence of such a fluid, and affirmed, as Leeuwenhoek did, that the
swelling subsequent to the bite of Culex was due to the irritation produced by
the tearing of the mouth-parts in the skin, without the aid of a poisonous
secretion. After having experimented a large number of times with the living
mosquito, I am convinced that there is use made of a poisonous saliva; for,
when biting, if the mosquito fails to strike blood, which it often does on parts
of the back of my hand, it may have inserted its proboscis (labium of course
excepted) nearly full length, in from one to six directions, in the same place
and withdrawn its proboscis; indeed it may have inserted its proboscis, as often
occurs, in extremely sensitive parts ; yet in such cases, if no blood be drawn, no
more effect is produced upon my skin than is produced by the prick of a sharp
needle; a red point appears only to disappear in a few hours. Certainly there
has been as much tearing of tissues in such a case as the above-mentioned, as
there is when Cule,T settles on a place richer in blood, and, with a single probing,
draws its fill. When the insect is allowed to draw its fill on the back of my
hand, the subsequent swelling lasts from forty to forty-eight hours, and th9
amount of poisonous effect upon me, as proved by numerous experiments, is in
direct proportion to the length of time which the Cidex has occupied in actually
drawing blood. The above-mentioned facts would indicate a constant outpouring
of some sort of poisonous fluid during the blood-sucking process, and would
necessitate a tube or channel for its conduction. Now no other channel exists
through which saliva could pass from the base to the tip in the mouth-parts which
Ctde,r inserts in the skin, and this, together with the position occupied by the

♦ "Das8 weder das Labrum noch die Hypopharynx eine vollstandige Rohre besitzt,
sondem nur einen Kanal/^



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salivary duct in other diptera, leads me to believe, without as yet being able to
give anatomical proof of it, that the hypopharynx of Cidex contains a duct that
pours out its poisonous saliva. Not having fresh specimens of Cvlex cUiatus,
and the extreme minuteness of the hypopharynx in the species of Cvlex available,
has precluded my determination of the actual presence of glands in connection
with this mouth-part.

The mandibles (figs. 1 and 8, w), the most delicate of the mouth-parts ot
Cidex, are two very thin linear-lanceolate lamellae of transparent chitin, which
rest with their inner edges beneath each half of the hypopharynx, their outer
edges projecting beyond its outer edge, on each side. The mandibles are so thin
and transparent, and so tightly pressed upon both the hypopharynx above and
the maxillae below, that they easily remain undiscovered in sections of the pro-
boscis. At the base of the proboscis they appear to have no muscular attach-
ments, but to lie imbedded in the connective tissue, beneath the pharynx and
above the maxillae. (See fig. 9.) They are slightly tapering from the base to
the tip, but are of equal thickness throughout their breadth ; at the tip they
have a slight thickening, in form of a letter V, with its opening turned toward
their very delicate, almost invisible tip. (See fig. 5, m.j

The maxillae (mistaken by Gerstfeldt* for the mandibles), are tapering
lamellae of chitin, apparently serrate at the tips. Each maxilla is thicker near
the inner edge, the thickening being formed by a solid chitinous shaft, which is
fixed longitudinally upon the upper side. (See fig. 5 and 8, fnx.) The bases of
the maxillae join the stouter maxillary palpi just before passing under the cly-
peus, and immediately afterwards they join the labium, and become imbedded,
with the mandibles, in connective tissue. (See fig. 9, nix.) Their continuations
in the head are two delicate chitin-supports, each of which ends in a strong
muscle; this muscle, the retractor maxillae (fig. 10, rm), passes backward and
downward through the head, beneath the infraoesophageal ganglion, and has its
origin in the posterior basal part of the head. The maxillae probably have no
protractor muscle, their forward motion being due to the elasticity of the chitin
frame-work of the head. The shaft of the maxillae is very transparent, except
near the inner side where the chitin-rod runs; here it is brownish and more
opaque. Out from the above-mentioned chitin-rod extends a very delicate
feathering, or corrugation, of chitin to the edge of the most transparent portion

* Gerstfeldt* (p. 33) says, "of which the mandibles, toothed at the end, are somewhat
broader but of the same length as the toothless maxillae." In the original, "von welchen
die am Ende gezahnten Mandibeln etwas breiter, aber ebenso lang als die zahnlosen
Maxillen smd."



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of each maxilla, as seen upon the basal portion of fig. 5, m^. In some species
of CuUx this feathering is right-angled with the direction of the chitin rod; in
other species oblique-angled, with the angle pointing forward, so as to
form a series of barblike corrugations. The tip of the maxillae (fig. 5, mx)
is very acute, has none of the before-mentioned chitinous corrugations, but, in
their place, near the outer edge, is a row of papillae, which have their tips
slightly recurved toward the head, and consequently appear serrate. These papillae


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Online LibraryGeorge DimmockThe anatomy of the mouth-parts and of the sucking apparatus of some Diptera → online text (page 2 of 7)