Article beginning on page 231.
Psyche 3:231-240, 1880.

Full text (searchable PDF)
Durable link: http://psyche.entclub.org/3/3-231.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

. PSYCHE.
ANATOMY OF THE MOUTH-PARTS AND OF THE SUCTORIAL APPARATUS OF CLZEX.*
BY GEORGE DIMMOCK, CAMBRIDGE, MASS.
(With Plate 7.)
FROM early times the mosquitoes, Cu-
lex of different species, have attracted the attention of mankind, and many at-
tempts have been made to settle various
points of their anatomy and life-history. Of their anatomy nothing- is, perhaps, of more interest than a study of their pro- boscis. While the importance of the
mouth-parts in the classification of insects remained undiscovered until Fabricius, in the last century, made them a basis for
dividing the insects into classes and gen- era, considering that they furnished suf- 3cient and constant characters, and far
more natural genera ;"I and their homo-
logical significance remained a mystery
until Saviyny,' in 1816, showed that the mouth-parts of all insects were reducible to the same general plan as those of
* Extract, with additions and changes, from " The anatomy of the mouth-parts and of the sucking ap- paratus of some diptera. Dissertation for the pur- pose of obtaining the philosophical doctorate at the Leipzig University, by George Dimmock, of Cam- bridge, Mass., U. S. A. Boston, A. Williams & Co., 1881." t.-p. cover, t.-p., 50 [+Io] p., 4 pi., 24.5X 19, t 12.5x 17.
chewing insects, and that these mouth-
parts were the serial homologs of locomo- tory appendages ; yet, previous to the
before-mentioned dates, a number of au-
atomists, attracted, probably, as much by the minuteness of the objects and the
difficulty of the work as by the popular interest which the mosquito excites,
sought to complete our knowledge of the
number, position and use of the mouth-
parts of this insect. The earliest of
these anatomists whose work is worthy
of note is Swammerdanim, who studied
Cdex in 1668.3 The difficulty of the
work which Swammerclamm undertook,
with the crude apparatus at that time at his command, can be easily comprehen-
ded when we consider that the proboscis
of the female of most species of Culex
has about the diameter of a hair from
the human head, that is, a diameter of
about one tenth of a millimetre ; that it is composed (see pi. 1, fig. 8) for the
most part of the sheath, within which
are six so-called setae, later to be more fully described ; and that these setae are I Fabricius, J. C. Systema entomologiae, . .. 1775. of transparent chitin, one of them being Preface.
so trans~arent and delicate that it has of- 2 Savigny, J. C. Memoires sur les animaux sans vertkbres. I. partie, I. fascicule. M6m. I.-11. . . . 3 Swammerdamm, J. Bybel der natuure . . . 1737- -.
1816. 1738. [I have used the German editionof 1752.1



================================================================================

232 PS rcHå .
ten been overlooked by later naturalists. dried, but only a channel open on one
Swammerdamm determined correctly.the side, Maumur also arrived at the idea number of setae in the proboscis of that the maxillary palpi of Culex could, the female, but he, erroneously, evidently in some cases, help to form the sheath supposed that the proboscis of the male
which encloses the setae, but he does not had the same number of setae aa that of
clearly say that they always do so in the the female. He erroneously thpught males. the setae to be capable of protrusion Since Reaumnr'a time but little has from the end of the sheath, without flex- been added to our knowledge of the ion of the latter, and that the largest of mouth-parts of a x , some writers fol- the five setae formed an inner sheath for lowing the statements of Swammerdamm, the other four.
He writes (p. 147) in others those of Maumur, or of Leeu- quaint-old style, " I consider that these wenhoek, in regard to the number of five setae serve, like BO many sharp little aetae. Among others I will cite Sul~ei',~
awls, to make the opening in the sweat-
who says, four to five pointed tub-
pores of the skin.
When this is clone ules ;" Fahricina,l who writes, " sheath they are drawn back again into the inner exserted, univalvular, flexible, with five sheath. This then enters (according to setae ; " J ordens? describes four setae : my idea) into the wound with its sharp Gra~enhorst,~ iL The proboscis long, eeti- cavity, and the mosquito mcks through form, five-parted ;" MeigenQ describes it the blood, which ascends alongside of four setae and figures five ; Gerstfeldt1O and between the little setae into the belly L ' The sheath is formed of the under lip of the mosquito." alone, and contains six setae;" Pa&- Leeuwenhoek, according to %aunmr, ard,ll " These six bristle-like organa are found only four eetae in the sheath of the folded together within the hollowed la- proboscis, and considered that the inner bium ; " Clans la writes, proboscis b& ex- aheath, described by Swammerdamm, tended with four setae ; " MuhrI8 figures was a channel, and not a closed tube.
setae.
Earth,4 wboae dissertation I have lately examined, thought the inner sheath was
6 Sulirer, J. H, Die Kennzeichen der Insekten . . . a closed tobe. Rbaum~r,~ in 1738, pub- 1761- 7 JSrdens, J. H. Entomologie und Helminthologie lished a long description of the month-
des mensc hlichen Kin-pen,
parts of Cftleas, and described å´wit great 8 Gravenhorst, J. L. C. Grundzuge der systetna- accuracy its mode of biting.
JEKanmur
tischen Natweschichte . . , 1817.
9 Meigen, J. W. Systematische Beschreibung found *' the six which dm bekannten europliixhen zwiflUge1iget-i Insekten the proboscis contains. He favored the . . . 1818-1838. idea that the inner sheath, which Swam-
10 Gmtfeldt, G.
Ueber die Mundtheile der san-
merdmm had described, was tot crlin- g e ~ ~ \ ~ ~ ~ ~ : to tie .fin- 4 Barth, J. M.
Dissertation de culice .. . 1737.
sects. ... 1869.
5 Rfiaumur, R. A. F.
Mhoires pour servir a
is Claw, C.
Grundzflge der Zoologie . . . 1876.
I'histoire des insectes. .. . [Edition 1737-1748, t 4, (3 Muhr, J.
Die Mundtheile der Insekten dar-




================================================================================

PSYCHE. 233
The unsettled state of our knowledge above-mentioned parts will be described of the anatomy of the mouth-parts of
more in detail later. la comparative size Calex, as can be seen by tile preceding and strength the mouth-parts would be ootes, led me to select this genus of di- arranged as follows, the largest and ptera for careful study, with the results stoutest first: labium, labrum-epipliw- noted in the following pages.
ynx (the name by which I designate
this compound piece in diptera), hypo-
IN THE FEMALE.
pharynx, maxillae and mandibles.
The mouth-parts which form the pro-
The general arrangement of the mouth-
boscis of the female Culex, as I have * parts, relative to each other, is shown found them by study of 0. r~fus, C. cili. best in fig. 8, which is a figure of a O~MS and C. pipiens, consist of a. labrum cross-section through the middle of the (pi. 1, fig. 1, lr) , an epipharyas (e) , a proboscis of a female Cdex TV.&B, while hypopharynx (A), two mandibles (m), in repose, with the set* sheathed in the and two maxillae (-nix), all sheathed, labium. The labhm (i), clothed on the
when in repose, in the labium (11, which outer side with its scales and hairs, is receives them into a groove on its upper wrapped nearly around the other mouth- side. Each maxilla has a maxillary pal- parts. In it tie the two maxillae (rn~)~ pub (mp), which lies outside the labium ; partly enclosing the parts above them, the latter has no palpi.
The labiom and and thus helping to bind the parts to- maxillary palpi are covered with hair and gether ; above the maxillae are the two scales ; the other mouth-parts are naked, maudiblea (nil, and immediately above light brown, setifotm and transparent ; . the mandibles, in the median line, is the they all originate at the anterior basal hypopharynx (4, with a thickened mid- portion of the head, and are, with the dle portiou. Resting on the hypo- exception of the maxillary palpi, of about pharynx is the 1aTbriim-epipharynx ; the equal length, that is, about three to four epipharyns (el, is omega-form in sec- times the length of the head.
The max- tion. and above it, delicately attached, is illary palpi, in the females of Culm the lahum (lr) . The changes in relative proper, are about the length of the head. position which the mouth-parts of Gulews The scaleless mouth-parts are not jointed, undergo as they approach the head can and are the ones which penetrate the skin be best (ascribed in the subsequent de- in biting. The labrum and epipharynx scription, in detail, of each separate are united in their whole length, forming part. a piece which is shown in section in fig. The labrum-epipharynx (figs. 1, 5. 6, 6, d.
The ofher mouth-parts are free to 7-8 ; Ir and e) of Cdex consists of the the base.
A pumping organ, trianguloid thin labrum resting upon and fastened to in cross-section (fig. 10, 61, is formed by the epipharynx ; it tapers graditally from a dilation of the oesophagus 'behind the base to apex. The epipharynx is omega- oesophageal nerve-ring. Each of the form in cross-section. being a chaunel



================================================================================

234 PSrCHB.
rather than a tube, a tube being formed
ing apparatus behind the oesophageal
by the pressing of the hypophaiynx nerve-ring, these muscles are the ones upon its under side. The tube thus that mustserve for suction. The section formed is the channel through which the represented in fig. 9 was talcen near the blood,
which CuZex sucks, passeis into base of the clypeus; a few sections fiw- the pharynx.
At its base or proximal ther on, posteriorly, the channel for the end the epipharynx is supported and passage of food turns upward and then moved by strong muscles having their backward again, passing in its course a insertions on the upper side of its wings place (fig. 11, v) where its walls ap- or lateral portions, and upon the upper proximate dorsally and ventrally. This side of its tube. These muselea extend narrowing of the walls is probably a upward and posteriorly, and have their valve to prevent the return of flnida to origin on the inner surface of the cly- the mouth during the pumping process. pew. (See figs. 9 and 11.) These The pharynx with its sorrottiiding mus- muscles (pin), by their contraction, ele- cle~ in CWex is the equivalent of what vate, and perhaps slightly retract, the has been termed the fulcrum in Musea.. epipharpx and the labrum to which they
MacloskieM writes of the fulcrum, It
are attached. These muscles probably seems to be general in diptera ; even the aid in suction for when the setae are all mosquito possesses it," bnt he does not tuck firm11 in the skin. the contraction further describe it. in other diptera than of these mtiscles would only serve to Musca. raise the base of the epipharyns from Thetipofthelabrum-cpipharynxseems that of the h.ypopliaryns; this action . to turn upward (fig. 1, Zr-e), although would tend to produce a vacuum between the opening is upon the ventral surface, the two (see fig. 9), and thus cause the as may be seen in fig. 6. b, which repre- blood to be drawn up in the tube of the seats the ventral view of the tip of this epipharynx. Tho probability that these part. The tip of the labrum-epipharps muscles aid in auction ie augmented by ia comparable to a quill-pen with three the fact, the explanation of which I have tips near each other, the middle one of more fully developed in the part of my these three tips being slightly shorter dissertation devoted to a comparison of than the other two. The two lateral the mouth-parts and suetorial apparatus portions of the epipharpx, as seen in in the different families of diptera upon section, when they near the tip, lay which I have worked, that the correspon- themselves closely upon the sides of the ding muscles are devoted to suction in tubular portion, passing upward upon it, other. flies, which cannot raise their as seen in fig. 5, lr-e; they thus serve to epipharps from their other month-parts ~trecgtheu the two outerpoints of the so freely as is seen in fig, 1, and further, that in the mde
ddex, which does not 14 Macloskie, G: The proboscis of the house-fly. (Amer. naturalist, March 1880, v. 14, p, 133-161, fig. possess - as does the female - a pump-
1-3.)




================================================================================

tip of the epipharynx, while the labriiin the under wall of the pharynx.
(See
continues to a sharp point at the tip,
fig. 11, A,) The hypopharynx is closely
and, united with the tipper surface of the pressed upon the under side of' the epiph aryux tube, forms the middle point epiphary nx, completing the tube nearly of the tip. The channel, or slit, fitoiig formed by the epipharynx. No muselea the under side of the epiph~iryns, widens have their insertion on the base of the
toward the tip (fig. 6, &) , leaving thus hypopharynx. Its tip is simply lanceo-
an opening for the passage of fluids into late (fig. 5, k). In Cvlex pipiens and
the tnbe of the epipharyux. C. rwfus nothing further is visible (with The labrum itself is a thiu lanceolate a magnifying power of five hundred lamella of chitin, concave along the un- diameters). in ~ections of the thicker der side from the basal portion to the middle portion of the hypopbryux, than tip, and its concavity rests upon and fits a, simple rod of chitiu ; but, in C. ciIuIf~ts, to the convexity of the tubular part of a North American species of which the '
the epipharyns, to which it is so lightly mouth-parts are larger, this rod appeared attached ,that they readily separate by
to be tubular. Is it a rod or is it a tube? application of caustic potash. The outer Menzbier16 writes (1). 25) that in di- edges of the labrum roll slightly inward ptma " neither the labrum nor the bypo- toward the epipharynx along most of its pharynx possesses a completed tube, but length. (See fig. 6, d.) At its base the only a channel " which leads into the labrum sends a chitiuous support beneath salivary duct. That Menzbier is incor-
the clypeus, where it separate6 more rect in affirming that the hypopharynx from the epipharyux and has its own. has no complete tube I have clearly muscles, indicating that the labrom has proved in my observations on Bwn-bylms a degree of motion independent of the and Efiatal/å´s but the question still re- epipharyns, a motion allowed, perhaps, mains unsettled whether Oulex has any by the elasticity of the connection be- passage, either tube or groove, through tween the labrnrn and epipharyus. The the hypopharynx. Reaumur8 (tome 4, muscles of the labrum (fig. 9, pn) are part '2, p, 396) discusses the probability inserted upon the upper side of its base of a poisonous fluid being secreted by and have their origin on the inner surface Culex, to cause the blood to fiow more of the root' of the clypeus.
These mus- readily when it bites, and eince his time cles are, at least in the females of Culex writers have, on the one hand, accepted rwfus, divided iuto three portions in their this statement, without proving the upper pnrt, as shown in fig. 9. presence of such a fluid or of the glands The hypopharyux of the
female of to secrete it, or they have, on the other Cules'; is a linear, lanceolate, transparent hund, denied the existence of swih & lamella of chitin, with a loneitudinal rod



================================================================================

236 PSTCHE.
ftuid, and-affirmed, as ~eeuwkhoek did,
through which saliva could pas5 from the that the swelling subsequent to the bite base to the tap in the mouth-parts which of Was was due to the irritation pro-
Cvlm inserts in the skin, and this, to-
due& by the tearing of the mouth-parts gether with the position occupied by the in the skin, without the aid of a poison- salivary duct in other dipbra, leads me
ous secretion. After having experiment-
to believe, without as yet being able to ed a large number of times with the
give anatomical proof for it, that the
living mosquito, I am convinced that hypopharynx of C'iitex contains a duct there is use made of a poisonous saliva ; that pours out its poisouous saliva. for, when biting, if the mosquito fails to Having no fresh specimens of Cwlew strike blood, which it often does on parts dÌöa(m and the extreme minuteness of of the back of my hand, it may have the hypopharynx in the species of Culex inserted its proboscis (labium of course available, has precluded my detemina- excepted) nearly full length, in from one tion of the actual presence of glands in to six directions, in the same place, and connectiou with this mouth-part. withdrawn its proboscis ; indeed it may The mandibles (figs. 1 and 8, m), the have inserted its proboscis, as often oe- most delicate of the month-parts of Qn- curs, in extremely sensitive parts; yet lex, are two very thin lineai^laneeolate in such cases, if no blood be drawn. no lamellae of transparent chitin, which rest more effect is produced upon my skin with their inner edges beneath each half than is produced by the prick of a sharp of the hypopharynx, their outer edges needle ; a red point appear8 only to dig- projecting beyond its outer %dge, on
appear in a few hours. Certainly there each side. At the base of the proboscis has been as much tearing of tissues in they appear to have no museulw attach- such a case as the above-mentioned, as ments. They are slightly tapering from
there is when Culev settles on a place
the haw to the tip, but are
of equal
richer in blood. ad, with a single pro- thiekuess thronghout their breadth; at bing, draws its fill. When the insect is the tip they have a alight thickening, in allowed to draw its fill on the back of my form of a. letter V, with its opening hand, the subsequent swelling lasts from turned toward their very delicate, almost forty to forty-eight hours, aud the amount invisible tip. (See fig. 5, wi. ) of poisouons effect upon me, as proved
The maxillae (mistaken by Gerstfeldt1å
by numerous esperimenta, is in direct for the rnandi blea, but correct.iy figured by proportion to the length of time which
MuhP on his diagram as maxillae) are
the Cuh has occupied in actually draw-
tapering lamellae of chitin, apparently
ing blood. The above-mentioned facts serrate at the tips. Each maxilla is would indicate a constant outpouring of thicker near the inner edge. the thick- some sort of poisonous fluid during the eniug being formed by a solid chitinous bloodsucking process, and would news- shaft. which is fixed longitudinally upon &itate a tube or channel 1'or its conduc- the upper side. (See 'fig. 5 and 8, via.) tion. Now no other channel exists The bases of the maxillae join the stouter



================================================================================

maxillary palpi just before passing under the clypens, said immediately afterwards they join the labium, and become im-
bedded, with the mandibles, in conuce-
tive tissue. (See fig. 9, mx. j Their
continuations in the bend are two delicate chitin-eapports, 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 infraoesophagea.1 ganglion, and has
its origin in the posterior basal part of the head. The maxillae probably have
no protractor muscle, their forward mo-
tion being h e to the elusticity of the
chifciii 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 del- icate feathering, or corrugation, of chitin to the edge of the most transparent por- tion of each maxilla, as seen upon the
basal portion of fig. 5, mx. The tip of
the maxillae (fig. 5. mx) is very acute, has uone of the before-mentioned c'hiti- nous corrugations, hut, iu their place,
near the outer edge, is row of papillae, which have their tips slightly recurved
toward the head, and consequently ap-
pear serrate. These papillae are upon
the upper surface of the maxillae, as
can be readily seen, by preparing the
month-part8 by lateral pressure, as in
fig. 1.
The maxillary palpi (fp. 1, 2, and
9, mp) are four-jointed in some spe-
cies of Culex, five-jointed iu others.
At first sight they appear to be three-
jointed, hiit more careful examinatiou
serves to show that the apparent basal
joint is made up of two joints, and
oftentimes to reveal a very short, knob- like joint at the extremity of what ap-
pears to be, at first, the apical joint. At their base the maxillary palpi join
the masillae just before the latter paaa beneath the dypew, and, with the max-
illae, join the other month-parts, as
shown, h section, by fig. 9.
The function of the maxillae is, prob-
ably, to draw the other mouth-pa$s into
the skin, when Culex bites, for if one
watches the maxillary palpi
of Cidex,
while the setae are entering the skin,
the setae seem. to pierce the skin, and. enter it with a slow gliding motion, as if drawn from below, instead of pressed.
from above ; meanwhile, if one observes
carefully, with a lens, the maxillary palpi can be seen to be in an alternating mo-
tion, as if the maxillae to which they are attached, pressed, first one then the
other, into the skin. and then pulled the other parts after them. The muscles,
retractores maxillaruin, already de-
scribed, lend weight to this view of the functions of the barbed maxillae.
The labium (figs, I, -2, and 3, l), the
largest of the mouth-parts of Culew, and the only one of them, helping form the
proboscis, which contains muscles, forms a sheath opening along the upper side,
and receiving in its channel the other
mouth-parts (excepting the maxillary
palpi), as seen in cross-section in fig. 8 ; it tapers from base to tip. ie flexible, has a delicately annuiated structure.
and is clothed with hair and scales. At
its base it unites with the maxillae,
mandibles, and hypopharynx, and con-




================================================================================

Throughout its length it contains, on
much as a carpenter guides his bit with
each side, muscles, which have their his fingers, while boring a piece of plank origin in the base of the head and serve When the setae of Cdex have entered
to control the motions of the labium.
the skin to nearly their full length the (See @s. 8 and 9, ml.) At the sides of
labium is bent double beneath the body
the tip of the labium are attached two
of the insect, the labellac still holding Iobiform appendages, the labelhe, which
the base of the setae at the point where are seen at % in fig. 3 with the tme tip they enter the skin. When the mos- of the labium proper between them. quito wishes to withdraw the setae it These terminal lobes are jointed to the probably first withdraws the two barbed labium, a little distance behind its tip, maxillae beyond the other setae, that as can be seen in fig. 7, which is a cross- is, so that their barbs, or papillae, will section of the labiom a trifle anterior to .be kept out of action by the mandibles the actual centre of motion of these and hypopharyiis; then it readily with- joints. The section of that portion of draws the setae, perhaps aiding their the labium which extends forward to withdrawal by the muscles of the labium, form ita tip is seen in the middle of the for, during the process of extracting the figure, just below the section of the eetae from the skin, while they are slow- maxillae (mx).
Outeide the section of . ly sinking back into the groove upon
each lobe is seen the section of a portion the upper eide of the straightening la-
of the exterior edge of the labium itself, bium, the mosquito keeps the labellae which here forms a double socket, or presaedfirmly upon the skin. pair of acetabula, into which the heada The mouth-parts of &dux, as above of the two labellae are set.
Each of the
described, are suspended under a cly-
lobes of the labium, - the labellae, - pem, or epistom, which is figured from is provided with an extensor aud flexor the side in fig. 1, c; from above in fig.