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Vol. Ill

ILLINOIS BIOLOGICAL
MONOGRAPHS

October. 1916

No. 2

THE HEAD-CAPSULE AND MOUTH
PARTS OF DIPTERA

WTTir TWENTY-FTVn: PI.ATK S

ALVAH PETERSON

PRICE $a.oo

Published by the University of Illinois
Under the Auspices of the Graduate School
Urbana, Illinois

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ILLINOIS BIOLOGICAL
MONOGRAPHS

Vol. Ill October, 1916 No. 2

Editorial Committee

Stephen Alfred Forbes William Trelease

Henry Baldwin Ward

Published under the

Auspices of the Graduate School by

THE University of Illinois

\THE HEAD-CAPSULE AND
MOUTH-PARTS OF DIPTERA

WITH TWENTY-FIVE PLATES

ALVAH PETERSON

MAY 15 1924

\'^^f.r.\ 'S^^

Contributions from the
Entomological Laboratories of the University of Illinois No. 52

THESIS

Submitted in Partial Fulfillment of the Requirements tor the

Degree of Doctor of Philosophy in Entomology

in the Graduate School of the

University of Illinois

191S

TABLE OF CONTENTS

PAGE

Introduction 7

Methods 8

Acknowledgments 9

Materials 9

Fixed Parts of the Head 13

Epicranial Suture 14

Fronto-clypeus 17

Tormae 19

Ptilinum 20

Labrum 20

Vertex _ 21

Compound Eyes and Ocelli 22

Occiput and Postgenae 2$

Tentorium 26

Movable Parts of the Head 32

Antennae 33

Mandibles 34

Maxillae 36

Labium 41

Epipharynx and Hypopharynx ; 49

Summary _ 54

Bibliography 57

Explanation of Plates 61

177] HEAD OF DIPTERA — PETERSON

INTRODUCTION

The head and mouth-parts of Diptera offer a rich field for research.
A number of excellent studies have been made by several investigators
and they deserve careful consideration. A review of practically all the
literature shows that a majority of the workers have examined only one
or a few species. Meinert (1881) and Hansen (1883), however, studied
a number of forms, but they were mostly specialized species ; while an
important study by Kellogg (1899) deals only with the families of the
Nematocera. Becher (1882) is the only investigator who has studied a
large series of generalized and specialized species. I have made a special
effort to secure as many generalized and specialized species as possible,
since it is highly desirable and essential in homologizing structures to
have at hand a wide range of species.

Extensive studies have not heretofore been made, so far as I know,
on the head-capsule ; consequently the important relationship which ex-
ists between the mouth-parts and the head-capsule in generalized insects
has not been traced in Diptera. This relationship is just as significant
in ascertaining the correct interpretation of the mouth-parts of Diptera
as it is in other orders. Its importance is illustrated by a study of the
head and mouth-parts of the Thysanoptera (Peterson, 1915).

A review of the literature, Dimmock (1881) or Hansen (1883),
discloses the many and varied interpretations that have been given to
the mouth-parts of Diptera. To arrive at a correct interpretation of the
fixed and movable parts of the head, the head-capsule and mouth-parts
of all the species studied, irrespective of the established systematic
position of the species, have been carefully compared with the head and
mouth-parts of generalized insects. On the basis of this comparison,
generalized, hypothetical types have been constructed for each fixed
and movable part. Each hypothetical type is made up by an accumu-
lation of all the generalized characters found among the Diptera, and
should show an intermediate stage between generalized insects and Dip-
tera. The use of such a hypothetical type is a great aid not only in
showing how the dipterous type has been developed, but also in deter-
mining the homology of the parts.

The scope of this investigation makes it necessary to limit the dis-
•cussions to the general subject of homology; consequently many details

8 ILLINOIS BIOLOGICAL MONOGRAPHS [178

of structure and other interesting modifications, shown in the figures
but without direct bearing on the subject of homology, are necessarily
disregarded. The fixed and various movable parts of the head are dis-
cussed separately, as developed from the hypothetical types, the discus-
sions in every case proceeding from the generalized to the specialized.

All the general conclusions pertaining to the head and mouth-parts
presented in the following pages are based entirely on a study of the
species listed under "materials", unless otherwise stated. General
statements in respect to the mouth-parts are true only for species having
them well developed.

The names here adopted for the sclerites of the head and mouth-
parts have been made to agree, so far as possible, with the terms now
in common use for the same parts in generalized insects. The terms
most commonly used thruout the literature for structures peculiar to
this order have been adopted unless clearly unsuitable ; and new terms
have been applied only to structures described here for the first time
and to parts to which the current names are inappropriate.

METHODS

The greater part of this study was made from dried specimens that
had been soaked from two to twenty-four hours in a 10% solution of
potassium hydroxide. The sclerites of weakly chitinized forms show
more clearly when they have been soaked for only a short time. After
soaking, the heads were washed in distilled water to remove the potas-
sium hydroxide and then preserved in 70% alcohol.

All dissections were made under a binocular microscope in 70%
alcohol in deep watch-glasses or in carbol-aniline oil. Studies and
figures were largely made from dissected parts in alcohol. Cleared
preparations mounted in balsam were also found useful. In making
such preparations the parts were dissected, stained, and cleared in
carbol-aniline oil. This oil evaporates slowly, will mix readily with
safranin or orange G dissolved in 95% alcohol, and will clear from
any grade of alcohol above 50%. The staining of material with safranin
before mounting proved to be very useful in diiferentiating the almost
colorless parts of some species. When using aniline oil it is necessary
to remove as much as possible of the oil before mounting, otherwise the
balsam will eventually darken.

The material for sections was fixed with hot (80° C.) corrosive
sublimate (saturated corrosive sublimate in 35% alcohol plus 2% of
glacial acetic acid) for fifteen minutes to two hours. This was replaced
by 70 %> alcohol containing a few drops of iodine, and the material was
allowed to remain in this for twenty-four or more hours. Paraffin hav-

179] HEAD OF DIPTERA— PETERSON 9

iug a melting point of 62-64 C. was a sufficiently firm medium in which
to cut sections as thin as eight microns. Specimens stained in toto gave
the best results. Delafield's haematoxylin required 24—48 hours, and
borax carmine 3-7 days.

ACKNOWLEDGMENTS

This investigation was carried on under the supervision of Dr.
A. D. MacGillivray, and to him I am greatly indebted for the sincere
interest shown and the many valuable suggestions received. Many speci-
mens, unobtainable in this vicinity, were secured from the collections
of the Illinois State Laboratory of Natural History, and for these I am
indebted to Professor S. A. Forbes. I am indebted to the Graduate
School of the University of Illinois for funds used in purchasing speci-
mens. I am also indebted to Mr. J. R. Malloch, of the Illinois State
Laboratory of Natural History, for the identification of all my material
and for specimens and many suggestions ; to Mr. J. M. Aldrich for
species of Diopsidae, Phycodromidae, and Blepharoceridae ; to Professor
A. L. Melander for a species of Cyrtidae ; to Mr. 0. S. Westcott for a
species of Phycodromidae ; to Dr. P. S. Welch for a species of Simulii-
dae ; and to Dr. 0. A. Johannsen for species of Dixidae and Blepha-
roceridae. I am also indebted to many others who furnished me with
unnamed material.

MATERIALS

The following list of insects includes all of the identified forms
studied. The families of Diptera to which these species belong are
arranged according to Aldrich 's "Catalogue of North American Dip-
tera". The generic and specific names of all but a few species may
likewise be found in this catalog.

Aldrich lists fifty-nine families ; of these, one or more representa-
tives of fifty-three families have been studied. The following are not
represented : Orphnephilidae, Acanthomeridae, Nemestrinidae, Apio-
ceridae, Rhopalomeridae, and Nycteribiidae. The male and female of
each species have been observed except in a few cases ; in these the word
"male" or "female" after the species name indicates which sex has
been seen. Excepting one or two forms, the male and female have both
been drawn if they were decidedly difi'erent. If the two sexes are
similar, the figures were mostly made from the female. An asterisk
before the name of a species indicates that this form has been embedded,
sectioned, and studied. The figures following the various species refer
to the drawings made of the same.

10 ILLINOIS BIOLOGICAL MONOGRAPHS [180

DiPTERA

Suborder Proboscidea

Orthorrhapha-Nemocera.

Tipulidae.— *Tipula bicornis (Fig. 18, 95, 178, 277, 383, 384, 388,
and 503), Tipula cunctans, Tipula abdominalis, Limnobia im-
matura, female (Fig. 93, 386, and 507), Helobia punetipen-
nis, female (Fig. 385), Trichocera bimacula, male (Fig. 16, 78,
158, 200, 260, 311, 365, 499, and 500), Geranomyia canadensis,
male (Fig. 382 and 506), Ptyclioptera rufocincta (Fig. 15),
and Bittacomorpha clavipes, male (Fig. 85 and 389).

Dixidae.— Dixa clavata (Fig. 19, 79, 163, 199, 262, 375, 387, 501,
and 502), and Dixa modesta (Fig. 254).

Psychodidae.— Psychoda albipennis (Fig. 8, 82, 166, 202, 263, 318,
372, 529, and 530), and Psychoda sp.

Chironomidae. — Chironomus ferugineovittatus (Fig. 12, 88, 89, 152,
206, 207, 270, 312, 371, 531, and 532), Culicoicles sanguisugus
(Fig, 253, 265, and 521), and Forcipomyia cilipes.

Culicidae.— Psorophora ciliata (Fig. 10, 26, 96, 159, 210, 211, 251,
266, 373, 380, 381, 504, and 505), Anopheles sp., and *Culex sp.

Mycetophilidae.— Sciara varians (Fig. 17, 81, 150, 205, 267, 314,
360, 512, and 513), Mycetobia divergens (Fig. 7, 90, and 161),
Mycetophila punctata (Fig. 11 and 87), and Leia oblectabilis
(Fig. 368).

Cecidomyiidae. — Eabdophaga strobiloides (Fig. 6, 86, 170, 201, 268,
313, 367, 510, and 511), and Cecidomyia sp.

Bibionidae.— Bibio femoratus (Fig. 13, 14, 91, 92, 153, 154, 208,
264, 315, 364, 522, and 523), and Bibio albipennis.

Simuliidae.— Simulium venustum, female (Fig. 2, 77, 144, 204, 250,
258, 316, 366, 489, 497, and 498), Simulium johannseni (Fig.
3 and 252), Simulium pecuarum, and Simulium jenningsi.

Blepharoceridae. — Bibiocephala elegantula (Fig. 4, 5, 76, 83, 155,
156, 203, 256, 269, 399, 526, and 527), and Blepharocera sp.

Ehyphidae.— Khyphus punctatus (Fig. 9, 80, 157, 209, 261, 321,
374, 508, and 509).
Orthorrhapha-Brachycera.

Stratiomyiidae.— Stratiomyia apicula (Fig. 27, 28, 104, 160, 213,
273, 331, 395, 396, 545, and 546), and Stratiomyia meigeni.

Tabanidae.— Tabanus giganteus (Fig. 20, 21, 74, 75, 142, 143, 214,
255, 259, 283, 317, 390-392, and 494-496), Tabanus sulcifrons,
Tabanus atratus, Tabanus trimaculata, and Chrysops striatus.

Leptidae.— Leptis vertebrata (Fig. 34, 35, 103, 145, 218, 275, 323, 369,

181] HEAD OF DIPTERA— PETERSON U

370, 520, and 525), Clirysopila proxima, Chrysopila thoracica,

Chrysopila quadrata, and Chrysopila velutina.
Cyrtidae.— Oncodes costatus (Fig. 53, 105, 109, 220, 486, and 487),

Eulonchus tristis (Fig. 284a, 364a, 425a, 425b, and 543), and

Pterodontia flavipes.
Bombyliidae.— Exoprosopa fasciata (Fig. 29, 98, 162, 216, 285, 361-

426-429, 549, and 550), Systoechus vulgaris, Lepidophora sp.,

and Bombylius major (Fig. 482).
Therevidae. — Psilocephala liaemorrhoidalis (Fig. 33, 36, 100, 173,

281, 324, 402, 403, 533, and 534).

Scenopinidae. — Scenopinus fenestralis (Fig. 41, 42, 107, 149, 219,

282, 325, 400, 401, 537, and 538).

Mydaidae.— Mydas clavatus (Fig. 30, 99, 146, 212, 271, 319, 397,

398, 535, and 536).
Asilidae. — Promachus vertebratus (Fig. 22, 84, 147, 148, 217, 276,

322, 376-379, and 517-519), Asilus notatus, and Deromyia um-

brina.
Dolichopodidae.— Dolichopus bifractus (Fig. 43, 112, 168, 226, 284,

432-434, 524, and 528), Dolichopus sp. (Fig. 108), Psilopodi-

nus sipho, and Sympycnus lineatus.
Empididae.— *Empis clausa (Fig. 26, 40, 97, 164, 215, 274, 352,

421-423, 547, and 548), Rhamphomyia glabra (Fig. 424 and

425), and Euhybus sp.
Lonchopteridae.— Lonchoptera lutea (Fig. 37, 102, 177, 223, 280,

320, 406-408, 539, and 541).
Phoridae.— Aphiochaeta agarici (Fig. 31, 111, 174, 224, 278, 335,

393, 394, 540, and 544), Metopina sp., and Dohrniphora con-

cinna.
Cyelorrhapha-Athericera.

Platypezidae.— Platypeza velutina (Fig. 32, 110, 165, 222, 272, 326,

415, 416, 542, and 542a).
Pipunculidae. — Pipunculus cingulatus (Fig. 38, 39, 106, 151, 243,

279, 327, 435, 436, 561, and 562).
Syrphidae.— Eristalis tenax (Fig. 23-25, 113, 167, 232, 286, 328,

441-443, 587, and 588), Syritta pipiens, and *Allograpta ob-

liqua.
Conopidae. — Conops brachyrhynchus (Fig. 67, 117, 186, 221, 305,

356, 417-420, 591, and 592), Stylogaster biannulata (Fig. 359),

and Physocephala tibialis.
Cyelorrhapha-Calyptratae.

Oestridae.— Gastrophilus equi (Fig. 54, 138, 239, and 490-492).
Tachinidae.— Arehytas analis (Fig. 68, 124, 197, 247, 309, 353, 468,

469, 604, and 605), Siphona geniculata (Fig. 355 and 458),

12 ILLINOIS BIOLOGICAL MONOGRAPHS [182

Gonia capitata, Ocyptera carolinae, and Gymnosoma fuliginosa.
Dexiidae.— Thelaira leucozona (Fig. 65, 128, 196, 230, 301, 346, 473,

474, 595, and 596).
Sarcopliagidae. — Sarcophaga haemorrhoidalis (Fig. 66, 130, 191,

244, 310, 350, 477, 478, 602, and 603).
Muscidae.— *Musca domestica (Fig. 71, 72, 133, 194, 242, 304, 351,

465-467, 600, and 601), Calliphora vomitoria (Fig. 484 and

485), *Stomoxys calcitrans (Fig. 354, 479, 480, and 599), Myios-

pila meditabunda (Fig, 120), Pollenia rudis, Lucilia caesar,

and Calliphora erythrocephala.
Anthomyiidae.— Hydrotaea dentipes (Fig. 69, 70, 127, 195, 241, 308,

349, 475, 476, 597, and 598), Lispa nasoni (Fig. 116 and 481),

Dexiopsis lacteipennis, Coenosia aurifrons, and Cliortophila sp.
Cy clorrhapha- Acaly ptratae .

Scatophagidae. — Seatophaga furcata (Fig. 62, 135, 193, 246, 307,

357, 470-472, 593, and 594).
Heteroneuridae.— Heteroneura flaviseta (Fig. 49, 126, 176, 229, 298,

340, 459, 460, 589, and 590).

Helomyzidae.— Oecothea fenestralis (Fig. 48, 137, 192, 227, 290, 332,

452, 453, 580, and 581).
Borboridae.— Borborus equiniis (Fig. 63, 136, 188, 231, 294, 342,

437, 438, and 565-567), Limosina ferruginata, and Sphaerocera

pusilla.
Phycodromidae.— Coelopa vanduzeii (Fig. 58, 121, 182, 288, 337,

448, 449, 559, and 560).
Sciomyzidae.— Tetanocera plumosa (Fig. 55, 119, 180, 225, 302, 344,

463, 464, 584, and 586), and Sepedon fuscipennis.
Sapromyzidae. — Sapromyza vulgaris (Fig. 60, 115, 171, 248, 289,

329, 409, 410, 553, and 554), Sapromyza bispina, Minettia lupu-

lina, and Lonchaea polita.
Ortalididae. — Chrysomyza demandata (Fig. 64, 134, 181, 245, 295,

341, 456, 457, 557, and 558), Tritoxa incurva, Chaetopsis aenea,
Camptoneura picta, Pyrgota sp., and Eiimetopia sp.

Trypetidae.— Enaresta aequalis (Fig. 61, 131, 175, 240, 292, 347,

413, 414, 572, and 573), Trypeta alba, and Straussia longipen-

nis.
Micropezidae.— Calobata univitta (Fig. 44, 114, 183, 236, 296, 348,

446, 447, 551, and 552).
Sepsidae.— Sepsis violacea (Fig. 46, 118, 184, 234, 287, 334, 439, 440,

582, and 583), and Proehyliza xanthostoraa.
Psilidae.— Loxocera pectoralis (Fig. 59, 123, 169, 235, 300, 339, 461,

462, 570, and 571).

183] HEAD OF DIPTERA — PETERSON 13

Diopsidae.— Sphyracephala bicornis (Fig. 52, 94, 190, 293, 338, 450,

451, and 585).
Ephydridae.— Ochthera mantis (Fig. 56, 101, 187, 237, 297, 336,

444, 445, 483, and 574-577), Paralimna appendiculata, and

Parydra bituberculata.
Oscinidae.— Chloropisca glabra (Fig. 51, 132, 189, 306, 345, 430, 431,

555, and 556), Siphonella abdoniinalis, and Hij^pelates flavipes.
Drosophilidae. — Drosophila ampelophila (Fig. 45, 125, 172, 238, 291,

343, 454, 455, 563, and 564).
Geomyzidae.— Chyromya concolor (Fig. 50, 122, 179, 233, 299, 333,

411, 412, 568, and 569).
Agromyzidae. — Desmometopa latipes (Fig. 47, 129, 185, 228, 303,

330, 404, 405, 578, and 579).

Suborder Eproboscidea

Hippoboscidae.— Olfersia ardeae (Fig. 57, 139, 198, 249, 358, 488,
and 606), and Melophagus oviniis.

Orthoptera

Periplaneta orientalis (Fig. 514),
Melanoplus differentialis (Fig. 515).
Gryllus pennsylvanicus (Fig. 516).

Hypothetical and typical figures (Fig. 1, 73, 140, 141, 199h, 256h,
257, 362, 363, and 493).

FIXED PARTS OF THE HEAD

A hypothetical head-capsule of Diptera (Fig. 1) has a dorso-ventral
extension. The epicranial suture (e. s) is present on the meson, and
extends from the occipital foramen (o. f ) to a point on the cephalic
aspect ventrad of the antennae. At this point it bifurcates and the two
arms continue to the invaginations of the anterior arms of the tentorium
(i. a), which are situated at the dorso-lateral angles of the clypeus (c).
The three unpaired sclerites included within, or ventrad of, the fork of
the epicranial suture are the front (fr), clypeus (c), and labrum (1).
The fronto-clypeal suture is represented by a dotted line in the figure.
The vertex (v) includes all of the dorsal and cephalic aspects of the
epicranium except the front (fr), while the genae (ge) are the regions
of the vertex ventrad and mesad of the compound eyes. Two large
compound eyes (c. e) cover the lateral portions of the cephalic aspect.
Three ocelli (oc) are situated on the vertex. The occiput (occ) and
postgenae (po) constitute the caudal aspect of the head-capsule.

14 ILLINOIS BIOLOGICAL MONOGRAPHS [184

The tentorium (t) of the hypothetical head-capsule has three pairs
of invaginations, homologous with the invaginations in generalized in-
sects. The invaginations of the posterior arms (i.p) of the tentorium
are situated ventrad of the occipital foramen at the distal ends of chitin-
ized thickenings. The invaginations of the dorsal arms of the tento-
rium (i.d) are on the cephalic aspect near the antennae and adjacent
to the epicranial suture, while the invaginations of the anterior arms
of the tentorium (i.a) are situated in the epicranial suture and adjacent
to the dorso-lateral angles of the clypeus.

The heads of all Diptera have a dorso-ventral extension, and in this
resp(^t resemble the heads of many generalized insects. Some of the
primary sutures, sclerites, and invaginations of the head of such an
insect are present in a number of the Nematocera and in a few of the
Brachycera. The hypothetical head-capsule has been constructed from
these forms. The heads of the Acalyptratae and the Calyptratae are
highly specialized by the modification, union, reduction, and membra-
nous development of parts, consequently very few if any primary char-
acters remain which can be homologized with these structures. The
membranous development of areas has been the most important process
of specialization. The stippled areas on the figures show the extent
of the membrane. The various parts of the head-capsule are discussed
individually and in the order in which they were described for the
hypothetical type. The heads of Diptera naturally fall into two groups
according to the presence or absence of a frontal suture (fr.s) and a
ptilinum (pt). The forms without a frontal suture are the more gen-
eralized.

Epicranial Suture. — The epicranial suture of all insects originates
in the embryo. The stem of the suture on the dorso-meson represents
the line along which the paired parts of the head meet, while the arms
of the suture (a. e. s) represent the place of contact between the paired
sclerites of the head and the mesal unpaired sclerites. The epicranial
suture (e. s) of a hypothetical dipterous head corresponds to the above
description, and is homologous with the epicranial suture found
in the heads of generalized immature and adult insects of the more com-
mon orders. The following examples illustrate the homology between
the hypothetical type and other insects. The epicranial suture in the
larva of Corydalis, and in the generalized larvae of the Coleoptera, Lepi-
doptera, and certain Hymenoptera, is complete, and its two arms join
with the margins of the clypeus, as in the hypothetical type.

The epicranial suture of the adults of the Orthoptera, Hemiptera^
and Hymenoptera also resembles this suture in the hypothetical head,
providing the following interpretation of this suture is accepted. In

185] HEAD OF DIPTERA— PETERSON 15

the adults of Gryllus and Periplaneta it is complete and similar to that
of Corydalis except that a small portion of each arm is wanting about
the antennae and the lateral ocelli. The ventral ends of the arms are
commonly called the fronto-genal sutures, and they join with the clypeus
as in Corydalis. All insects that have a sucking type of mouth, such
as the Hemiptera and Hymenoptera, usually show no signs of the stem
of the epicranial suture. The arms, however, are distinct and form the
lateral and dorsal boundaries of the large mesal piece commonly called
the clypeus. A large number of the Diptera possess an epicranial suture
which closely resembles that of the Hemiptera and the Hymenoptera.
On the basis of the above interpretation of the epicranial suture it has
been possible to homologize the sutures and sclerites, and the invagina-
tions of the tentorium on the cephalic aspect. No other interpretation
gave satisfactory results.

The epicranial suture (e. s) in Mycetophila (Fig. 11) is complete
and closely resembles the hypothetical type. In Leia it closely resem-
bles that of Mycetophila except for the stem of the suture, which is
wanting dorsad of the median ocellus. The stem of the epicranial suture
in Psorophora (Fig. 10 and 26) and Chironomus (Fig. 12) is repre-
sented by a distinct suture in a deep fold on the meson. Other forms,
such as E/habdophaga (Fig. 6), Mycetobia (Fig. 7), and Tabanus (Fig.
20), show depressions or thickenings along the meson. These marks
may have no significance. Outside of the above-mentioned forms, the
stem of the epicranial suture is wanting.

The arms of the epicranial suture (a. e. s) are present in many
Diptera. This is the case in all but a few of the Nematocera, in a ma-
jority of the Brachycera, and in many of the families of the Cyclorrha-
pha. These resemble, therefore, the adults of the Hemiptera and Hy-
menoptera. The arms are present as definite sutures between two
chitinized areas in Tabanus (Fig. 20 and 21) and Leptis (Fig. 35),
and in the female of Simulium (Fig. 2). The epicranial suture is ap-
parently wanting in the male of Simulium (Fig. 3) unless the lateral
margins of the convex area represent it. In many genera the epicranial
suture is represented by the edge of a chitinized sclerite. This is the
case in Chironomus (Fig. 12), Trichocera (Fig. 16), Psorophora (Fig.
10), Mycetobia (Fig. 7), and Dixa (Fig. 19). The vertex in the genera
just named is membranous between the antennal fossae and the epicra-
nial suture. Sciara (Fig. 17 ) , Khabdophaga (Fig. 6), Bibiocephala (Fig.
4 and 5), and possibly Rhyphus (Fig. 9) and Bibio (Fig. 14), have
the arms of the epicranial suture represented by the chitinized margin
of the vertex, which is adjacent to the membranous portion of the
fronto-clypeus. The location of the invaginations of the arms of the

16 ILLINOIS BIOLOGICAL MONOGRAPHS [186

tentorium usually helps to determine the location of the epicranial su-
ture. In Ptychoptera (Fig. 15) the invaginations of the anterior arms
of the tentorium are located in the distinct V-shaped depression on the
chitinized area ventrad of the antennae. Undoubtedly this depression
marks the position of the epicranial suture. Tipula (Fig. 18) has a
very specialized head and shows no epicranial suture or tentorium.

Only the arms of the epicranial sutures are present in the Brachyc-
era. On the whole these sutures are not as well developed in the
Brachycera as in the Nematocera. When present (a. e. s) they are long
and slit-like in all the genera except Tabanus. This condition is due
to the fusion of the invaginations of the dorsal arms and the anterior
arms of the tentorium along each suture. The arms of this suture in
Tabanus (Fig. 20 and 21) unite the invaginations on each lateral half
of the head, but they are not decidedly slit-like.

The arms of the epicranial suture (a. e. s) in Tabanus (Fig. 20)
have the usual inverted-u shape and their ventral ends terminate at the
ventral margin of the head. The arms are indistinct ventrad of the
invaginations of the anterior arms of the tentorium. The invaginations
(i. a) in Promachus (Fig. 22) are slit-like and situated near the ventro-
lateral angles of the compound eyes. The epicranial suture is wanting
dorsad and ventrad of the invaginations of the anterior arms, and in
this respect Promachus differs from Leptis and Tabanus. From Leptis
(Fig. 35) it is possible to homologize the arms of the epicranial suture
of all the Brachycera and those of the Cyclorrhapha. The arms of the
suture in Leptis are long and slit-like and coincide with the invagina-
tions of the tentorium on the cephalic aspect of the head. They extend
dorsad from the ventral margin of the head to a point ventrad of the
antennae, where they unite and enclose a convex mesal area called the
fronto-clypeus (fr. c). This suture (a. e. s) in Platypeza (Fig. 32)
closely resembles that of Leptis. The dorsal ends of the arms of the
epicranial suture are wanting in Psilocephala (Fig. 36), My das (Fig.
80), Exoprosopa (Fig. 29), Eristalis (Fig. 23 and 25), and Scenopinus
(Fig. 41 and 42), and in other forms. Scenopinus shows a striking
variation in that the vertex is membranous between the antennae and
the fronto-clypeus, and no epicranial suture can be traced thru the
membrane. Stratiomyia (Fig. 27) shows a unique development of the
slits in that they extend mesad rather than dorsad. This condition is
undoubtedly a secondary development. The epicranial suture of Lon-
choptera, Aphiochaeta, Pipunculus, and Empis is discussed under fronto-
clypeus.

No epicranial suture or slit-like invaginations are present in any
dipteron that has a frontal suture (fr. s) or a ptilinum (pt). Since

187] HEAD OF DIPTERA— PETERSON 17

the tentorium on the cephalic aspect and the arms of the epicranial
suture are usually closely associated in insects, there is every reason to
believe that the tentorial thickenings (t. th) mark the course of the
suture (a. e. s). Furthermore, the location of the thickenings o'f the
tentorium is very similar to the location of the slit-like invaginations
of Leptis (Fig, 35). These thickenings (t. th) have been considered as
marking the course of the arms of the epicranial suture. The extent
of the tentorial thickenings varies considerably, as shown in the figures.
In Tetanocera (Fig. 55), Chloropisca (Fig. 51), Heteroneura (Fig. 49),
and others, the tentorial thickenings extend to the antennal fossae (a. f).
No sutures are present between the dorsal ends of these thickenings.

Fronto-clypeus. — The front (fr) and clypeus (c) of all insects are
unpaired sclerites located between the arms of the epicranial suture
(a. e. s). The labrum (1) is also an unpaired sclerite attached typically
to the ventral margin of the clypeus. These three sclerites and their
parts are not always distinguishable. This is particularly true of the
front and clypeus in Diptera. The dotted, transverse line uniting the
invaginations of the anterior arms of the tentorium (i. a) in the hypo-
thetical head indicates the position of the fronto-clypeal suture. In a
few of the Orthorrhapha, suture-like marks, depressions, or thickenings
extend across the chitinized portion of the fronto-clypeus. These marks
in Chironomus (Fig. 12), Mycetophila (Fig. 11), and Rhabdophaga
(Fig. 6) resemble the fronto-clypeal suture as indicated in the hypo-
thetical type. It is possible that they are remnants of this suture.
Excepting in the forms named, one can not be sure of the presence of
a fronto-clypeal suture ; consequently the entire area between the labrum
and the arms of the epicranial suture has been designated as the fronto-
clypeus (fr. c). The absence of the fronto-clypeal suture in Diptera
is not unusual, since it is wanting in many generalized insects. For
those who may wish to divide the fronto-clypeus into two areas, the
dorsal half would be the front and the ventral half the clypeus. A
large portion of the fronto-clypeus is membranous in Rhabdophaga (Fig.
6), Rhyphus (Fig. 9), and Sciara (Fig. 17), and the chitinized part
is greatly reduced. The variations found in the Nematocera are rep-
resented in the figures.

The Brachj'cera show two lines of development in the modification
of the area enclosed by the arms of the epicranial suture. Both of these
started from a form which possessed an epicranial suture similar to that
of Leptis (Fig. 35). The line of development seen in Psilocephala,
Platypeza, Scenopinus, Lonchoptera, and Aphiochaeta is considered first.
The chitinized fronto-clypeus of Leptis resembles the fronto-clypeus of
a number of the Nematocera, as Sciara (Fig. 17). From this simple

18 ILLINOIS BIOLOGICAL MONOGRAPHS [188

condition it is possible to develop the type of fronto-clypeiis found in
Psilocepliala (Fig. 33 and 36). This came about by a membranous
development on the meson and on the lateral margins of the fronto-
clypeus and the loss of the arms of the epicranial suture directly ven-
trad of the antennae. The membranous development of the fronto-
clypeus of Platypeza (Fig. 32) resembles that of Psilocepliala. Sceno-
pinus (Fig. 41 and 42) belongs to this same line, but in this genus the
antennae are adjacent to the fronto-clypeus and no portion of the
chitinized vertex exists between them. The form of the chitinized
portion of the fronto-clypeus resembles closely that of Platypeza (Fig.
32). Aphiochaeta (Fig. 31) and Lonchoptera (Fig. 37) apparently
belong to this same series. If such is the case, the arms of the epicranial
suture do not project dorsad but are represented by the nearly straight
ventral margin of the cephalic aspect. This condition must have come
about by the straightening out of the usual u-shaped depression, and
the chitinized part of the fronto-clypeus is located ventrad of the mar-
gin of the head. The tentorial thickenings along the ventral margin
of the head in Lonchoptera afford evidence favorable to the above inter-
pretation. A similar type of development occurs in Bibio (Fig. 14),
in which the invaginations for the anterior arms of the tentorium are
located on the ventral margin of the head-capsule latero-ventrad of
the antennal fossae. All the other Brachycera and Cyclorrhapha figured,
show the presence of sclerites designated as the tormae and located
ventrad of the fronto-clypeus, and this fact places them in the line of
specialization which leads toward a muscid type.

The fronto-clypeus (fr. c) is present in all Diptera and constitutes
a prominent portion of the head-capsule. In Tabanus (Fig. 20 and
21) the fronto-clypeus is the entire area ventrad of the epicranial suture
and outside of the tormae and the labrum. The sutures separating the
fronto-clypeus from the genae (ge) are very indistinct. No arms of
the epicranial suture are present in Promachus (Fig. 22), Empis (Fig.
40), and Pipunculus (Fig. 38) ; consequently the dorsal extent of the
fronto-clypeus can not be determined, and the area ventrad of the
antennae is considered as the fronto-clypeus. The fronto-clypeus of
Mydas (Fig. 30) resembles that of Leptis, and from a type similar to
Mydas it is possible to develop the fronto-clypeus of Exoprosopa (Fig.
29), Eristalis (Fig. 25), and probably Stratiom.yia (Fig. 27). The
fronto-clypeus of Mydas closely resembles that of the Acalyptratae and
the Calyptratae, as will be seen by comparing Mydas with Tetanocera
(Fig. 55), Chloropisca (Fig. 51), Chyromya (Fig. 50), and Musca (Fig.
72). It is not a completely chitinized area in all of the genera studied,
and the significance of this mesal membranous area in Sepsis, Oecothea,.
and Calobata has been suggested in the discussion on the ptilinum.

189] HEAD OF DIPTERA— PETERSON 19

Torniae. — The tormae (to) in generalized insects are chitinized
pieces which belong to the lateral portions of the epipharynx in the
region of the clypeo-labral suture and connect with the clypeus or la-
brum at the lateral ends of the suture. These are well illustrated in such
Orthoptera as Periplaneta (Fig. 514), Melanoplus (Fig. 515), and
Gryllus (Fig. 516).

The tormae of generalized Diptera also connect with the inner sur-
face of the ventral portion of the fronto-clypeus. They are not well-
developed structures or readily distinguishable from the fronto-clypeus
in a number of species of the Nematocera. This seems to be due to the
decidedly convex nature of the fronto-clypeus and the close proximity
of its lateral portions to the lateral margins of the epipharynx. The
tormae of Leptis (Fig. 520), Psilocephala (Fig. 36 and 533), Scenopi-
nus (Fig. 41 and 538), Aphiochaeta (Fig. 31 and 544) Lonchoptera
(Fig. 37 and 539), and Platypeza (Fig. 32 and 543) connect with the
fronto-clypeus and thus resemble the Nematocera and the hypothetical
type. In Tabanus, the tormae (Fig. 494) resemble the above genera in
their connection with the fronto-clypeus, but they have been enlarged
ventrad until they are exposed between the clypeus and the labrum
(Fig. 20 and 494). The exposed portions of the tormae resemble two
small, triangular sclerites with their pointed ends meeting on the meson.
This condition is not unusual since they resemble closely the exposed
portions of the tormae located at the lateral ends of the clypeo-labral
suture in Gryllus (Fig. 516). Simulium (Fig. 2 and 489) also shows
exposed portions of the tormae at the ventro-lateral angles of the fronto-
clypeus (fr. c).

The inverted chitinized V-shaped piece ventrad of the fronto-
clypeus in My das (Fig. 30) has undoubtedly been derived from the fusion
of the tormae of some form resembling Tabanus (Fig. 20). The tor-
mae are adjacent to the fronto-clypeus in Mydas, but they are not con-
nected with the same as in Tabanus. From the type of tormae found
in Mydas it is possible to develop the tormae of all other genera. The
tormae vary in shape and position as seen in the cephalic views of the
head. In Exoprosopa (Fig. 29), Eristalis (Fig. 25), and Stratiomyia
(Fig. 27) they show a striking development in that they are located
within deep emarginations of the ventral margin of the fronto-clypeus.
The tormae of Empis (Fig. 40) closely resemble those of Mydas and
belong to the same line of development. In Pipunculus (Fig. 38) the
tormae resemble the fronto-clypeus of Sciara (Fig. 17), but as a matter
of fact the fronto-clypeus is the area ventrad of the antennae, as shown
by the location (Fig. 151) of the dorsal arms of the tentorium (d. a).
The tormae of the Acalyptratae are usually crescent-shape, while in the
CJalyptratae they resemble the type found in Mydas.

20 ILLINOIS BIOLOGICAL MONOGRAPHS [190

Ptilinum. — A deep, inverted U-shaped groove is present in the
heads of all the Calyptratae and the Acalyptratae dorsad of the anten-
nae. This groove is called the frontal suture (fr. s) and marks the line
of invagination of the large membranous pouch, the ptilinum (pt). In
Sphyracephala (Fig. 52) the frontal suture is V-shaped, owing to the
peculiar development of the head. The extent of the invagination of
the ptilinum (pt) is indicated by a dot-and-dash line in the drawings
of the cephalic and lateral views of the head-capsule.

The origin of the ptilinum has been a mystery to morphologists.
After a careful examination of the heads of the Brachycera and the
Cyclorrhapha, no definite data were found which would throw any light
on its origin. A few forms, however, suggested a possible way in which
it might have been developed. The frontal suture and the ptilinum
are comparatively small in Tetanocera (Fig. 55), Saprorayza (Fig. 60),
Conops (Fig. 67), Ochthera (Fig. 56), and Chloropisca (Fig. 51).
These genera gave no clue to the early stages of its development unless
the thinly chitinized condition of the fronto-clypeus of Chloropisca has
some significance. It seems evident that the frontal suture was once a
membranous area which became invaginated to form a membranous
pouch or ptilinum. If this is the case, the mesal membranous area of
the fronto-clypeus of Sepsis (Fig. 46), Oecothea (Fig. 48), Calobata
(Fig. 44), and Desmometopa (Fig. 47) would be very significant. The
ptilinum might possibly have originated from some form similar to
Scenopinus (Fig. 41), in which the ventral margin of the chitinized
vertex is located dorsad and laterad of the antennae. It seems quite
possible that the membrane along this margin became invaginated in
the early stages of the development of the ptilinum. The above con-
jectures may or may not be correct. A real solution of the problem will
undoubtedly require a careful study of the pupal development.

Lahrum. — The labrum (1) of a hypothetical dipterous head (Fig.
1, 140, and 493) is a distinct, chitinized, tongue-like structure connected
with the ventral margin of the clypeus. The shape and size of the
labrum are identical with the shape and size of the epipharynx, which
is located on its caudal aspect. The labrum (1) and epipharynx (ep)
are joined together by a membrane along their lateral margins. These
two structures thus act as one organ and they have rightly been called
the labrum-epipharynx (1. ep). The above relation of the labrum to
the epipharynx and the fronto-clypeus resembles that in the Orthoptera.

In a general way the labrum of all the genera studied resembles the
hypothetical type described above. It varies, however, in shape and
in degree of chitinization. In Promachus (Fig. 22), in Psorophora (Fig.
10 and 26), and in the female of Tabanus (Fig. 20) it is completely

191] HEAD OF DIPTERA — PETERSON 21

chitinized and separated from the fronto-clypeus by a suture. In all
other genera there is a distinct membranous area present between the
fronto-clypeus and the labrum. This area is very extensive in the
Cyelorrhapha and includes the ectal exposure of the tormae. The la-
brum of a few scattered g6nera, such as Rhabdophaga (Fig. 6), Myceto-
bia (Fig. 7), Chironomus (Fig. 12), Scenopinus (Fig. 41), and others,
is completely membranous, while in still others it is nearly so, as in
My das (Fig. 30). The figures of the cephalic aspect of the head and
the lateral views of the epipharynx and the hypopharynx show the
shape and extent of the chitinization of the labrum.

The labrum of Dixa (Fig. 501), Trichocera (Fig. 499), Sciara
(Fig. 513), Bibio (Fig. 523), Simulium (Fig. 497), Culicoides (Fig.
521), Tabanus (Fig. 20), and Dolichopus (Fig. 528) is distinctly sepa-
rated from the epipharynx (ep) by a membrane. This condition is
best seen in a lateral view. A majority of the forms studied have little
or no membrane between the labrum and epipharynx. This is particu-
larly true of the Cyelorrhapha. The surface of the labrum of all Dip-
tera is more or less convex. In a large number of the genera the con-
vexity is very decided and of such a nature as to surround the cephalic
and lateral aspects of the epipharynx. The epipharynx in these forms
can only be seen in a caudal view. In the Calyptratae, the labrum and
epipharynx are firmly united in one piece.

The labrum of Simulium (Fig. 2 and 489) is unique in that the
chitinized part consists of a narrow mesal piece which bifurcates at its
distal end. These bifurcations give rise to special small hook-like struc-
tures (h) which have been incorrectly interpreted as mandibles (Smith,
1890). The labrum and epipharynx of Psorophora (Fig. 504) fit to-
gether very closel}^ By careful dissection they may be separated, as
seen in the drawing. So far as observed, no membrane is present be-
tween them. The proximal end of the labrum is crook-like in form,
and muscles connect with this portion.

Vertex. — The vertex (v) of a hypothetical head (Fig. 1) consists
of the paired continuous areas on the cephalic aspect of the epicranium.
It is interpreted as including all the cephalic and dorsal aspects of the
epicranium except the front. In a number of the Diptera, as heretofore
described, the stem of the epicranial suture (s. e. s) is present and marks
the line of fusion of the two halves of the vertex, upon which the ocelli
and the antennae are located. The shape and size of the chitinized
portion of the vertex is largely determined by the size of the compound
eyes, the location and extent of the membranous area about the base
of the antennae, and the location of the arms of the epicranial suture.
The variations in the size and shape of the vertex are shown in the figures
of the cephalic aspect of the head.

22 ILLINOIS BIOLOGICAL MONOGRAPHS [192

The region of the vertex ventrad and mesad of each compound
eye is a gena. The size of the genae (ge) is dependent upon the location
of the compound eyes and the ventral extension of tiie head-capsule.
The figures show considerable variation in these respects.

Compound Eyes and Ocelli. — The compound eyes (c. e) of a hypo-
thetical head are large oval structures located on the cephalo-lateral
aspects of the head-capsule. They cover from one-half to two-thirds
of the entire cephalic aspect and their caudal margins are adjacent to
the lateral margins of the head. The compound eyes of a majority of
the Diptera resemble in general the hypothetical type. The shape and
size vary considerably with the different species. Variations are most
prevalent in the families of the Orthorrhapha. This variability agrees
with the decided variability of other parts. In such genera as Tipula
(Fig. 95), Psorophora (Fig. 96), and Limnobia (Fig. 93) the compound
eyes are exceptional in that they extend onto the caudal aspect of the
head. The variations in shape are well illustrated by the numerous
figures.

The compound eyes show secondary characters in a greater number
of species than any other fixed or movable part. This sexual variation
is most prevalent among the Nematocera and the Brachycera, and was
not observed in the Acalyptratae. Among the Calyptratae, slight
differences occur in Musca (Fig. 71 and 72) and Hydrotaea (Fig. 69
and 70). When sexual variation occurs, the eyes of the male are larger
than those of the female, and they are usually adjacent along a portion
of their mesal margins. Such species are said to be holoptic ; while all
the females, and some of the males, having the eyes distinctly separated,
are dichoptic. The extent of the holoptic condition depends upon the
size of the eyes and the location of the antennal fossae, as in Simulium
(Fig. 2 and 3) and Bibio (Fig. 13 and 14). In the male of Bibio the
compound eyes are adjacent along their mesal margin and the antennal
fossae (a. f ) are located ventrad of the eyes. The extent and nature
of the sexual variation is shown in the figures. Except in the case of
Empis the heads of the male and female have both been drawn when
decided differences are present.

The facets or ommatidia of the compound eyes vary in number,
form, and size thruout the order. In the Nematocera they are usually
large and not as closely compacted as in the Cyclorrhapha. An inter-
esting variation occurs in the male of Simulium, the facets (fa) of the
ventral half of the eye being smaller than those of the dorsal half. This
difference is also found in the female of Bibiocephala (Fig. 5). In the
male of Bibio (Fig. 154) the facets (fa) in the ventro-caudal portions
of the eyes are smaller than the others. The compound eyes of Bibio-
cephala and Blepharocera are divided into a dorsal and a ventral por-

193] HEAD OF DIPTERA— PETERSON 23

tion by a transverse constriction (cli), where the ommatidia are wanting.
This constriction is also present in Bibio, but in this form it is confined
to the caudo-ventral portion of the eye.

The drawings of the lateral aspects of some heads show a line of
dashes or a solid line around the margins of the compound eyes. This
line indicates the extent of the infolding of the head-capsule adjacent
to the compound eye. This infolding, or ocular sclerite (o. s), is figured
only for those species in which it is closely related to the external mark-
ings found on the caudal aspect dorsad of the occipital foramen. The
influence of this invaginated edge will be more fully discussed later.

The three ocelli (oc) of the hypothetical head-capsule (Fig. 1) are
arranged in the form of a triangle and located on the cephalo-dorsal
aspect of the vertex. The median ocellus is in the epicranial suture,
somewhat ventrad of the lateral ocelli. In Leia it is in this suture
somewhat dorsad of the bifurcation, and the other two ocelli are some-
what laterad of it. This location of the ocelli in the Diptera agrees
with Comstock's idea concerning the caudal migration of the ocelli in
specialized insects. In generalized insects all three ocelli may be on the
front or two on the vertex while the median ocellus is on the front.
The ocelli in the Hymenoptera and Hemiptera are similar in location to
those of the Diptera.

Leia is the only form studied which has ocelli and a well-marked
stem of the epicranial suture. The chitinized, secondary, Y-shaped
thickenings on the ocellar triangle of Rhyphus (Fig. 9) and Mycetobia
(Fig. 7) should not be confused with the epicranial suture. Three ocelli
are present in all other genera of Diptera examined except Oncodes ( Fig.
53) and Mycetophila, in which there are only two. The median ocellus
is wanting in Mycetophila, while the lateral ocelli are small inconspicuous
bodies, adjacent to the dorso-mesal margin of the compound eyes (not
shown in the figure). The figures show such variations as occur in the
various ocellar groups.

Occiput and Postgenae. — No sutures occur on the caudal aspect of
the hypothetical head-capsule (Fig. 73) except the epicranial suture
(e. s). This absence of sutures makes it impossible to locate definitely
the boundaries of the occiput and the postgenae. The following in-
terpretation is based upon a study of the occiput and postgenae of
generalized insects, such as the Orthoptera. The occiput comprises all
the area dorsad of an imaginary transverse line drawn thru the middle
of the centrally located occipital foramen. The areas ventrad of this
line and laterad of the mesal membranous areas are the postgenae. The
occiput (occ) undergoes a secondary development about tlie margin of

24 ILLINOIS BIOLOGICAL MONOGRAPHS [194

the occipital foramen. The structures pertaining to this modification
have been designated as the parocciput (pocc). Each postgena (po)
is also secondarily differentiated along its mesal margin by a chitinized
thickening which extends between the occipital foramen and the invagi-
nations of the posterior arms of the tentorium. This thickening has
been designated as the parapostgenal thickening, while the area mesad
of it is the parapostgena (ppo). The two mesal projections of the
parocciput on the lateral margin of the occipital foramen serve as points
for the articulation of neck sclerites and mark the ventral boundary of
the occiput.

The occipital foramen (o. f ) is centrally situated in all but a few
genera, such as Tipula (Fig. 95), Limnobia (Fig. 93), Psorophora (Fig.
96), and Bibio (Fig. 92), in which it is near the dorsal margin. The
size of the occipital foramen is more or less constant thruout the order,
but in Psychoda (Fig. 82) and Promachus (Fig. 84) it is comparatively
much larger than in Pipunculus (Fig. 106) and Exoprosopa (Fig. 98).
The shape of the occipital foramen varies somewhat, but usually it is
in the form of a figure eight. The constrictions in the lateral margins
are generally due to the mesal projections of the parocciput, which
vary to some extent in their situation. The projections in Exoprosopa
(Fig. 98), Pipunculus (Fig. 106), and Mydas (Fig. 99) meet on the
meson and completely divide the occipital foramen into two openings.
The neck sclerites (n. s) always articulate with these mesal projections
and are represented in a number of the figures.

The occiput (occ) of all genera figured resembles in general the
occiput of the hypothetical head, since no sutures separate the vertex,
the occiput, and the postgenae. The position of the occipital foramen
and the contour of the caudal surface determine the amount of variation
in the occiput as well as in the postgenae. In some genera, Empis (Fig.
164) and Bibiocephala (Fig. 156), the caudal aspect is convex; while
in others, Exoprosopa (Fig. 98) and Pipunculus (Fig. 106), it is de-
cidedly concave. Suture-like markings or depressions are present near
the dorsal margin of the caudal aspect in the heads of Tabanus (Fig.
74), Stratiomyia (Fig. 104), Bibio (Fig. 91), Bibiocephala (Fig. 83),
Leptis (Fig. 103), Psilocephala (Fig. 100), and others. These depres-
sions mark the place of contact of the mesal portions of the ocular
sclerites with the head-capsule, and are in no way homologous with the
sutures about the occiput in generalized insects.

The area about the dorsal and lateral margin of the occipital fora-
men, the parocciput (pocc), is more or less differentiated from the re-
mainder of the occiput in all the species studied. In the more generalized
forms, Bibiocephala (Fig. 83), Trichocera (Fig. 78), Tipula (Fig. 95),

195] HEAD OF DIPTERA— PETERSON 25

Sciara (Fig. 81), and Bittacomorpha (Fig. 85), it is only a thickened
edge ; but in a large number of species thruout the order it is a clearly-
defined piece, set off from the occiput proper by a secondary suture.
The indefiniteness of this piece in a large number of the generalized
Diptera and the want of an homologous part in generalized insects
support the view that it is only a secondary modification of the occiput.

The parocciput (poce), in most genera, occurs as a narrow piece
about the dorsal and lateral margin of the occipital foramen, and its
ventral ends project mesad. In the heads of the Cyclorrhapha three
secondarily developed, chitinized thickenings (th) arise from the ental
surface of the parocciput; two of these project dorso-laterad from the
lateral portions of the parocciput, and the third is on the meson. These
thickenings are also present in some of the Brachycera, such as Dolicho-
pus (Fig. 112). Their greatest development is found in Eristalis (Fig,
113), where two dorso-lateral thickenings (th) extend to the caudal
margins of the compound eyes and a third thickening, on the meson,
bifurcates a short distance dorsad of the occipital foramen, the two arms
connecting with the dorso-mesal angles of the compound eyes. In the
genera figured, the dorso-lateral thickenings are, on the whole, better
developed than the thickening on the meson. In Thelaira (Fig. 128)
and Musca (Fig, 133) the dorso-lateral thickenings project dorsad to
the margin of the head. The area included between them is called by
several writers the epicephalon, or the occiput; and tho it is entirely
different in origin from similarly situated areas in Tabanus (Fig. 74)
and other genera, the same name is applied in the different cases. These
names and others used by systematists have no morphological signifi-
cance for they can not be homologized with the primary sclerites of a
generalized insect.

The postgenae (po) of the hypothetical dipterous head have been
carefully compared with those of the heads of such generalized insects
as the Orthoptera. The mesal membranous area between the postgenae
is homologous with the membrane of the neck and with the membrane
surrounding the proximal ends of the maxillae and the labium. There
are no sutures or sclerites along the mesal portions of the postgenae in
such generalized insects as the Orthoptera ; consequently the parapost-
genae (ppo) described above can not be homologous with any primary
sclerite. In Diptera the parapostgenae are undoubtedly special modi-
fications of the postgenae.

The postgenae and the parapostgenae of a majoritj^ of the Nematoc-
era resemble those of the hypothetical head. In Chironomus (Fig,
88) and Trichocera (Fig, 78) the parapostgenal thickenings are want-
ing. The invaginations for the posterior arms of the tentorium in

26 ILLINOIS BIOLOGICAL MONOGRAPHS [196

Simulium (Fig. 77) are adjacent to the occipital foramen, consequently
the parapostgenae are confined to the lateral margins of the occipital
foramen. In Tabanus also the invaginations are adjacent to the occipi-
tal foramen, and the postgenae are connected ventrad of the occipital
foramen in the male and by a narrow strip in the female.

The area ventrad of the occipital foramen is a continuous chitinized
piece in all of the Cyclorrhapha and the Orthorrhapha. There is only
one probable explanation of the origin of this area. It has been derived
from the fusion of the mesal margins of the postgenae. The evidence
for this interpretation is found in a number of the Nematocera. The
mesal margins of the postgenae in Trichocera (Fig. 78) and Sciara
(Fig. 81) are curved mesad and in some cases actually join, as in the
female of Bibiocephala (Fig. 83). The peculiar elongated heads of
Limnobia (Fig. 93), Tipula (Fig. 95), and Psorophora (Fig. 96) show
a distinct depressed line on the meson along which the postgenae have
joined. In a number of the genera of the Orthorrhapha and the Cy-
clorrhapha the ventral margin of the caudal aspect is decidedly concave.
This condition may be due to a former stage in the development of the
fused postgenae. In all cases where the area ventrad of the occipital
foramen is chitinized, the invaginations of the posterior arms of the
tentorium are somewhat adjacent to the occipital foramen and the
attachments of the maxillae are removed to or beyond the ventral mar-
gin of the head. Sciara (Fig. 81) is a good example of an early stage
in the development of the above relationship. The variations in the
shape and extent of the postgenae and the parapostgenae are well illus-
trated by the figures.

Tentorium. — There is present within the head of generalized insects
a definite arrangement of chitinized rods and plate-like structures which
go to support the internal organs and furnish places for the attachment
of muscles. These rods or plates arise from three pairs of openings on
the head known as the invaginations of the anterior arms, dorsal arms,
and posterior arms of the tentorium. The invaginations of the anterior
arms are usually associated with the lateral margins of the clypeus,
with one of the points of articulation of the mandibles, and frequently
with the ventral ends of the arms of the epicranial suture. The invagi-
nations of the dorsal arms are associated with the points of attachment
of the antennae and near the dorsal portions of the arms of the epi-
cranial suture. The invaginations of the posterior arms are associated
with the occipital foramen and the points of attachment of the maxillae.
The three pairs of arms unite within the head ; the small dorsal arms
unite with the larger anterior arms, and these, in turn, join with the
posterior arms, which are confined to the caudal portion of the head-

197] HEAD OF DIPTERA — PETERSON 27

capsule. The free ends of the posterior arms are fused and form the
body of the tentorium.

The tentorium undergoes a considerable amount of variation in
the different orders, but so far as observed the above associations be-
tween the invaginations and the fixed and movable parts of the head
are always retained by the more generalized members of each order.
This is also true for a generalized hpothetical dipterous head. The
tentorium (t) of such a head (Fig. 140 and 141) is considerably modi-
fied when compared with the tentorium of a generalized insect. Two
pairs of invaginations are present on the cephalic aspect of the head
(Fig. 1). The dorsal, indistinct pair (i. d), just ventrad of the anten-
nae, are homologous with the invaginations of the dorsal arms of the
tentorium, while the prominent pair (i. a) of invaginations ventrad of
these and located in the arms of the epicranial suture (a. e. s) and
adjacent to the lateral ends of the fronto-clypeal suture are the invagi-
nations of the anterior arms of the tentorium. One pair of invagina-
tions (i. p) is present on the caudal aspect of the head-capsule (Fig.
73) somewhat ventrad of the ventro-lateral margins of the occipital
foramen. These are the invaginations of the posterior arms of the
tentorium. Each lateral half of the tentorium is Y-shaped (Fig. 141),
the stem of the Y arising from the invaginations on the caudal aspect,
its caudal portion being a part of the posterior arms (p. a) of the tento-
rium. The large ventral arm of the Y and the cephalic portion of its
stem, constitute the anterior arm (a. a), and the small dorsal arm of
the Y is the dorsal arm (d. a) of the tentorium. These two arms con-
nect with their respective invaginations on the cephalic aspect. The
body of the tentorium (b. t) is apparently represented by a small, rudi-
mentary, mesal projection arising from the posterior arms near the
caudal portion of the stem of the Y.

The association between the movable appendages and the invagi-
nations of the tentorium is discussed under the respective appendages.
From this point, the tentorial structures as they occur in the various
genera are compared with the hypothetical type and the line of speciali-
zation noted. The forms without a ptilinum are considered first. The
parts of the free tentorium, not completely fused with the head-capsule,
are indicated in the figures by dotted lines.

The tentorium of Tabanus (Fig. 142 and 143) is generalized and
closely resembles the hypothetical type ; consequently it furnishes a
good starting point for a discussion. Two pairs of invaginations are
present on the cephalic aspect (Fig. 20) ; of these the invaginations for
the anterior arms (i. a) are the more prominent. The dorsal arms
(i. d) arise from the head-capsule just ventro-laterad of the antennae

28 ILLINOIS BIOLOGICAL MONOGRAPHS [198

and connect with the arms of the epicranial suture (a. e. s). The in-
vaginations of the anterior arms are situated near the ventral ends of
the arms of the epicranial suture. The invaginations on each lateral
half of the head are joined together by the arms of the epicranial suture
and resemble the hypothetical type. Two pairs of invaginations are also
present on the cephalic aspect of Simulium (Fig. 2 and 3), but in this
genus they are not as prominent as in Tabanus. They are situated on
the vertex (v), adjacent to the compound eyes. In the female the arms
of the epicranial suture are well defined and the invaginations are
closely adjacent to them, while in the male the sutures are wanting.
Tabanus and Simulium are the only forms figured which show two
distinct pairs of invaginations on the cephalic aspect. All other genera
have only one pair and these are of two types. They are either long
and slit-like or they resemble small pits or darkened spots on the ectal
surface. The long slit-like invaginations found in Leptis (Fig. 35),
Psilocephala (Fig. 36), Platypeza (Fig. 32), Scenopinus (Fig. 41),
Exoprosopa (Fig. 29), Stratiomyia (Fig. 27), Mydas (Fig. 30), Erista-
lis (Fig. 25), and other genera have a special significance which will
be more fully discussed later. The small, pit-like invaginations are
present in the Nematocera and in Pipunculus (Fig. 38) and Empis
(Fig. 40). These are situated on the chitinized area of the vertex; or
on the fronto-clypeus, adjacent to the arms of the epicranial suture and
usually close to the compound eyes. Their position and structure indi-
cate that they are the invaginations of the anterior arms of the tento-
rium. In a few of the genera of the Orthorrhapha and in some others,
as Lonchoptera (Fig. 37), Tipula (Fig. 18), and Aphiochaeta (Fig.
31), no invaginations are present on the cephalic aspect of the head.

One pair of invaginations, that for the posterior arms (i. p) of
the tentorium, is present on the caudal aspect of the heads of all genera
examined except Oncodes (Fig. 105), Olfersia (Fig. 139), Tipula (Fig.
95), and perhaps a few species of other genera in which it is difficult
to be sure of their presence. These invaginations in Bibiocephala (Fig.
83), Trichocera (Fig. 76), Dixa (Fig. J9), Rhyphus (Fig. 80), Sciara
(Fig. 81), Psychoda (Fig. 82), Rhabdophaga (Fig. 86), Chironomus
(Fig. 88), Bittacomorpha (Fig. 85), Mycetophila (Fig. 87), and Myce-
tobia (Fig. 90) are decidedly ventrad of the occipital foramen and
adjacent to the proximal ends of the maxillae. They are connected
with the lateral margins of the occipital foramen by means of the para-
postgenal thickenings except in Chironomus and Trichocera. The above-
named forms closely resemble the hypothetical type. In a few genera
of the Nematocera, such as Psorophora (Fig. 96) and Simulium (Fig.
77), the invaginations are adjacent to the occipital foramen. This

199] HEAD OF DIPTERA—PETERSON 29

position is characteristic of these invaginations in the Brachycera, and
the figures show the details of the variations in the position of the
invaginations on the posterior arms of the tentorium.

Two lines of specialization appear in the tentorium of the Diptera,
one in the reduction of the dorsal arms and the other in the union of the
dorsal arms with the anterior arms. The two types of invaginations
described for the cephalic aspect of the head bear directly upon this
problem. The most important evidence in proof of these two types of
development is found in the structure of the arms.

In Seiara (Fig. 150), Bibio (Fig. 153 and 154), Psorophora (Fig.
159), Trichocera (Fig. 158), Bibiocephala (Fig. 155), Dixa (Fig. 163),
and others, two long narrow rods extend on each side between the
invaginations on the caudal aspect and the invaginations on the cephalic
aspect. These rods are composed of the posterior arms (p. a) and the
anterior arms (a. a) of the tentorium. The dorsal arms are completely
reduced in these forms. Other genera show completely developed dorsal
arms or rudiments of the same. The dorsal arms (d. a) are distinct
and free in Pipunculus (Fig. 151). They arise from the anterior arms
and project cephalad to the cephalic aspect of the head, where they
connect with small but distinct ental projections adjacent to the anten-
nae. The cephalic ends of the dorsal arms are very delicate and easily
broken in dissecting. There are no invaginations on the ectal surface.
In Chironomus (Fig. 152) the tentorial arms are swollen near the mid-
dle of their length, and the distinct humps on the dorsal side are
interpreted as rudiments of the dorsal arms. Promachus (Fig. 147)
has two long, free, finger-like projections, arising from the ocular
sclerite near the antennae, which project toward the tentorium proper.
These projections are apparently dorsal arms of the tentorium, or
derivatives of the same that have retained their connection with the
ocular sclerite near the mesal margin of the compound eye but have lost
their connection with the tentorium proper. A similar relationship
exists between the dorsal arms and the ocular sclerite in Tabanus (Fig.
22). If the above structures in Promachus are dorsal arms, then the
anterior arms are large (Fig. 148) and the slit-like invaginations on the
cephalic aspect are only the invaginations of the anterior arms of the
tentorium.

The tentoria of the Nematocera above described are in the ventral
half of the head-cavity and their situation is dependent upon the posi-
tion of the invaginations. Usually the invaginations of the anterior
arms are ventrad of the invaginations of the posterior arms ; but Bibio-
cephala (Fig. 155) is an exception to this rule if the tentorium in this
genus is composed of only the anterior and posterior arms — and there

30 ILLINOIS BIOLOGICAL MONOGRAPHS [200

is no evidence to the contrary. In some genera, as in Lonchoptera
(Fig. 177), Ehabdophaga (Fig. 170), and Empis (Fig, 164), the tento-
ria are not free rods extending thru the head cavity, but are completely
united with the ventral margin of the head, or nearly so. The tentorium
of Aphiochaeta (Fig. 174) is reduced to two small ental projections
adjacent to the occipital foramen, while in Tipula (Fig. 178) the ten-
torium is apparently wanting.

In a majority of the Brachycera the tentorial arms are specialized
by fusion, and Tabanus (Fig. 143) illustrates an early stage in this
development. The principal difference between the tentorium of Taba-
nus and the hypothetical type is the presence of a thin chitinized plate
in the V-shaped opening between the anterior and dorsal arms. Simu-
lium (Fig. 144), of the Nematocera, has a similar plate, and these two
genera clearly demonstrate the first stage in the fusion of these two
arms. The cephalic end of the tentorium in Mydas (Fig. 146), Leptis
(Fig. 145), Scenopinus (Fig. 149), and Exoprosopa (Fig. 162) is a
broad uniformly chitinized triangular area. This condition is accounted
for on the basis of the union of the anterior and dorsal arms. The
invaginations on the cephalic aspect of these forms agree in all respects
with this interpretation. In Tabanus (Fig. 20) the invaginations on
each side are joined together by the epicranial suture, while in the
above forms the invaginations are slit-like and occupy the greater part
of the arms of the epicranial suture. The slit-like invaginations are
easily explained if the anterior and dorsal arms are considered as united.

The posterior arms of the tentoria of the Nematocera and the
Brachycera vary in shape, size, and location. The anterior and posterior
arms are united within the head and no sharp line can be drawn be-
tween them. The body of the tentorium (b. t) is represented by small
projections on the mesal surface of the posterior arms of most genera.

Many interesting features occur in the modifications of the tentoria
of this group. In Dolichopus (Fig. 43 and 168) it appears to be fused
with the dorsal margin of the slit-like openings on each side between
the mesal margin of the compound eye and the fronto-clypeus. The
tentorium of Mydas (Fig. 146) is large and tubular, and it is possible
to push a good-sized needle thru the opening on the cephalic aspect to
the opening of the posterior arms on the caudal aspect.

The tentoria of the genera possessing a ptilinum differ principally
from the foregoing in the degree of fusion with the head-capsule. In
most genera of this group the tentorium is completely united with the
head, but in a number of the Acalyptratae the tentorial arms arise as
free rods from the invaginations on the caudal aspect and project to
the latero-ventral margins of the head-capsule, with wliich they unite

201] HEAD OF DIPTERA— PETERSON 31

and continue cephalad as thickenings adjacent to the ventral margin
of the head, as in Sapromyza (Fig, 171), Loxocera (Fig. 169), Euaresta
(Fig. 175), Calobata (Fig. 183), Chrysomyza (Fig. 181), Drosophila
(Fig. 172), Chyromya (Fig. 179), Heteroneura (Fig. 176), and Teta-"
nocera (Fig. 180). In those forms where the tentorium is completely
fused with the head, as in Sepsis (Fig. 184), Chloropisca (Fig. 189),
Coelopa (Fig. 182), and Borborus (Fig. 188), it is a continuous thick-
ening from the latero-ventral angle of the occipital foramen to the
cephalo-ventral aspect of the head-capsule. The tentorium between the
invaginations for the posterior arms and the ventro-lateral margins of
the head-capsule is apparently wanting in Musca (Fig. 194), Thelaira
(Fig. 196), Archytas (Fig. 197), and some other genera; in one or
two cases it is possible to trace a faint mark which would indicate the
line of connection. The tentoria of some of the genera of the Acalyp-
tratae and the Calyptratae show an unusual development of the tento-
rial thickenings (t. th) in that they extend about the entire caudal part
of the ventral margin of the head. In some cases these tentorial thick-
enings reach the occipital foramen, as in Calobata (Fig. 114), Scatoph-
aga (Fig. 135), Heteroneura (Fig. 126), Lispa (Fig. 116), and Myios-
pila (Fig. 120), while in Musca (Fig. 133), Coelopa (Fig. 121),
Hydrotaea (Fig. 127), and other genera, there is no such connection.

The invaginations of the posterior arms of the tentorium of the
Acalyptratae and the Calyptratae are situated laterad or latero-ventrad
of, and adjacent to, the occipital foramen. In many of the species
figured the invaginations are merely long, heavily chitinized furrows
extending latero-ventrad from the occipital foramen, and very often
it is difficult to locate them definitely.

Two mesal projections arise from the proximal portions of the
posterior arms in a majority of the Cyclorrhapha. In some species
these structures are well developed, and their mesal ends apparently
join on the meson, cephalad of the occipital foramen. These structures
are similar to those described for the Brachycera and are rudiments of
the body of the tentorium.

No invaginations of the tentorium occur on the cephalic aspect in
any of the forms which possess a ptilinum. On account of the decided
specialization of this aspect, it is very difficult to know just what has
happened. The tentorium is represented by thickenings which extend
from the ventral to the cephalic aspect of the head. The extent of
these thickenings varies; in some genera they continue to the antennal
fossae, while in others they are practically wanting.

32 ILLINOIS BIOLOGICAL MONOGRAPHS [202

MOVABLE PARTS OF THE HEAD

In arrangement and structure the movable parts of the head of
the generalized Diptera are homologous with the movable appendages
of other generalized insects. In the Cyclorrhapha the parts retain their
relative position, but structurally they undergo striking modifications
and in some cases almost complete reduction.

To make clear the use of a number of terms found in the following
discussions, the mouth-parts as a whole will be considered at this point.
The appendages of the mouth of the generalized Diptera are free, inde-
pendent structures, with their proximal ends adjacent to the head-cap-
sule. The cardines and stipites of the maxillae are exceptions to the
above statement, in that they are embedded in the mesal membranous
area of the caudal aspect of the head. The mouth-parts, the labrum-
epipharynx, and the hypopharynx constitute in the Calyptratae a single
complex mouth-appendage designated as the proboscis. The chitinized
parts of the proboscis are far removed from the head-capsule, but in
this projection of the parts, the proximal ends of the chitinized ap-
pendages are joined together and have the same relationship with each
other as in generalized insects.

The term proboscis is most applicable among the Cyclorrhapha to
those whose mouth-parts resemble those of Musca. The proboscis is
naturally divided into three areas by the two bends which it makes as
it is withdrawn into the oral cavity. The parts of the proboscis have
been given varied and confusing names. Hewitt divides it into two
general areas — the rostrum and the proboscis proper. He says: "The
proboscis consists of two parts, a proximal membranous conical por-
tion, the rostrum, and a distal half, the proboscis proper, which bears
the oral lobes. The term haustellum is also used for this distal half
(minus the oral lobes) and as a name it is probably more convenient,
as the term proboscis is used for the whole structure, — rostrum, haustel-
lum and oral lobes".

The terms rostrum and haustellum have been used in various ways
by numerous workers in different orders; consequently the parts which
they designate are by no means homologous. A more comprehensive
set of terms based upon the word proboscis has been used by a few
workers, who divide the proboscis into basiproboscis, mediproboscis, and

203] HEAD OF DIPTERA— PETERSON 33

distiproboscis. These terms have here been adopted. The basiproboscis
(bpr) is equivalent to the rostrum, and may be defined as the mem-
branous, cone-shaped area between the ventral margin of the head-
capsule and the proximal end of the theca. The tormae, labrum-
epipharynx, hypopharynx, and maxillae are parts of the basiproboscis.
The mediproboscis (mpr) is the median section of the proboscis and
includes the theca and the chitinized cephalic groove of the labium. It
is equivalent to the haustellum of most authors. The distiproboscis
(dpr), the enlarged dilated lobes at the distal end of the proboscis, is
composed of the paraglossae, with their pseudotracheal areas, and the
glossae. The distiproboscis is equivalent to the oral lobes, or labellae.
The movable appendages of the head are discussed in the following
order: antennae, mandibles, maxillae, and labium.

Antennae. — The antenna of a generalized hypothetical dipterous
head (Fig. 199h) is many-segmented and of a filiform type. All the
segments are similar excepting the two large proximal ones known as
the scape (sc) and the pedicel (pd). The scape articulates with the
chitinized antennal sclerite (a. s) which bounds the periphery of the
antenual fossa (a. f ) that is situated on the vertex dorsad of the arms
of the epicranial suture. The antennae of the hypothetical type resem-
ble the antennae of many generalized insects.

The antennae of a majority of the Nematocera resemble the hypo-
thetical type, and on the whole resemble each other. The variations in
shape and size can be seen in the figures. Secondary sexual variation
occurs in a few of the Nematocera, in which the antennae of the male,
illustrated by Chironomus (Fig. 207) and Psorophora (Fig. 211), bear
long flexible setae while those of the female are almost bare.

The antennae of the Brachycera show a wide range of development,
but in a majority of the genera figured the main line of specialization
is toward the type found in Lonchoptera (Fig. 223) and Dolichopus
(Fig. 226). One of the striking exceptions to this general line of de-
velopment occurs in the geniculate type found in Stratiomyia (Fig.
213). The antennae of the Brachycera have, as a rule, fewer segments
than the Nematocera. The scape and pedicel undergo only a slight
change, in this group, but the flagellum (fl) is greatly modified. The
proximal segment of the flagellum, or the third segment of the antenna,
is enlarged, while the remaining segments are so reduced in size as to
resemble the lash of a whip. The lash-like portion of the antenna is
called the arista (ar). The following genera suggest the various stages
thru which the antennae have passed in attaining the muscid type of
development. In Tabanus (Fig. 214), Empis (Fig. 215), Exoprosopa
(Fig. 216), Promachus (Fig. 217), and Leptis (Fig. 218) the flagellum

34 ILLINOIS BIOLOGICAL MONOGRAPHS [204

is stylate, and the third segment is large and conical, with one or more
segments at its distal end. The antennae of Platypeza (Fig. 222),
Lonchoptera (Fig. 223), Aphiochaeta (Fig. 224), Oecothea (Fig. 227),
and Dolichopus (Fig. 226) show an advanced stage of development in
which the third segment is large and round and the remaining segments
are lash-like and situated toward one side of the third segment. All
but a few of the antennae of the Cyclorrhapha have apparently devel-
oped from a type similar to the last-mentioned genera. The principal
differences between the antennae of this group are in the length and
breadth of the third segment and in the modification of the arista. The
antennae of Olfersia (Fig. 249) are of a reduced muscid type, and are
inserted in deep cavities on the cephalic aspect of the head ; the scape
and pedicel are greatly reduced, and the arista is merely a small pro-
jection on the lateral aspect of the large segment.

Antennal sclerites (a. s) are present only in Chironomus (Fig. 12
and 206) and Psorophora (Fig. 10 and 26). In these genera it is a
distinct chitinized ring about the proximal end of the scape. The extent
and place of the membrane with which the antennae are connected
vary considerably. In Trichocera (Fig. 16), Chironomus (Fig. 12),
Psorophora (Fig. 26), Mycetobia (Fig. 7), and some other genera it is
very extensive.

A general survey of the antennae of the Diptera shows that in the
Nematocera they are generalized and on the whole resemble each other.
The specialized antennae of the Cyclorrhapha in all but a very few
genera are of a muscid type, and also quite similar in form. The
antennae of the Brachycera present a few specialized types, but the
majority of them show intermediate stages between the forms found
in the Nematocera and those of the Cyclorrhapha.

Mandibles. — Only a few of the generalized Diptera possess mandi-
bles. They are present in the females of Simulium (Fig. 2 and 250),
Tabanus (Fig. 255 and 317), Psorophora (Fig. 159 and 251), Culicoides
(Fig. 253), Dixa (Fig. 254), and Bibiocephala (Fig. 155 and 256), but
wanting in the males of all the species examined except Simulium (Fig.
3 and 252). The males of Simulium johannseni and 8. jenningsi have
distinct mandibles. No other males of Simulium were examined. So
far as known this is the first record of a male dipteron possessing true
mandibles.

The hypothetical mandibles (Fig. 256h) of a dipteron are long,
thin, sword-shaped structures fitted for piercing. They thus resemble
the mandibles (md) of Tabanus (Fig. 255) and Culicoides (Fig. 253).
Tliey are situated between the clypeus, labrum-epipharynx, and max-
illae, and are closely associated with the invaginations of the anterior

205] HEAD OF DIPTERA— PETERSON 35

arms of the tentorium. Structurally the hypothetical mandibles do not
resemble the biting mandibles of the Orthoptera, but their situation
and their association with the invaginations of the anterior arms of the
tentorium are the same, which is far more important in determining
their homology than any particular form they may assume.

The mandibles vary in their structure. In Psorophora (Fig. 251)
they are long and needle-like, while in Tabanus, Culicoides, and the
male of Simulium (Fig. 252) they are sword-shaped, and in Dixa (Fig.
254) spindle-like. The mandibles in the females of all species of Simu-
lium (Fig. 250) examined are a trifle longer than those in the males
(Fig. 252) and much broader at their distal ends. The greatest spe-
cialization in structure and point of attachment with the head occurs
in the long, thin, saw-like mandibles of Bibiocephala (Fig. 256) and
Blepharocera. In these forms they are longer than the labium, blunt
at the end, and toothed along the mesal margin, fitting against a similar
edge on the lateral margin of the hypopharynx.

All mandibles (md) of the Diptera are connected with the head-
capsule cephalad of the maxillae (mx) and caudad of the labrum-
epipharynx (1. ep) and the fronto-clypeus (fr. c). In this respect they
resemble the hypothetical type. In Psorophora, Dixa, Simulium, and
Tabanus they are associated with the invaginations of the anterior arms
of the tentorium. The proximal ends of the mandibles of Psorophora
(Fig. 159) are bent cephalad, and articulate with the head-capsule at
the distal ends of the crescent-shaped tentorial thickenings (t. th) which
arise from the margins of the invaginations of the anterior arms of the
tentorium. In Dixa (Fig. 254) the mandibles connect with the head-
capsule at the ventro-caudal angles of the clypeus. An indistinct thick-
ening extends dorsad from the point of articulation of each of the man-
dibles toward the invaginations of the anterior arms of the tentorium.
The mandibles of Simulium (Fig. 250 and 252) and Tabanus (Fig.
317) connect with the head-capsule directly ventrad of the invagina-
tions of the anterior arms of the tentorium, but no direct connection
occurs between them. In the female of Simulium the mandibles artic-
ulate with a hook-shaped projection of the vertex. The mandibles of
Tabanus (Fig. 255) are bifurcate at their proximal end and the lateral
bifurcation articulates with the head. The location of the mandibles of
Bibiocephala (Fig. 155) and Blepharocera is generalized with respect
to their position between the maxillae and the fronto-clypeus, but their
point of attachment with the head-capsule is decidedly specialized.
They unite with ehitinized pillars (Fig. 83) on the caudal aspect
ventro-laterad of the invaginations of the posterior arms of the tento-
rium. The proximal portion of eacb mandible is a long ehitinized strip

Z6 ILLINOIS BIOLOGICAL MONOGRAPHS [206

embedded in the membrane. These strips extend cephalad from their
caudal connection to the cephalic margin of the membrane about the
mouth-parts. At this point, where distinct tendons are attached, they
turn abruptly ventrad and become free appendages. All connection
between the mandibles and the invaginations of the anterior arms of
the tentorium is lost. The relationship between the tentorium and the
mandibles has not been observed in Culicoides for the lack of material.
No other families of the Diptera outside of those to which the above-
named genera belong, so far as observed, possess true mandibles or
rudiments of the same. When mandibles are present, they are always
of considerable size and probably functional.

A number of investigators have described mandibles for many
species not included in the above families. Langhoffer (1901) describes
mandibles for the Doliehopodidae which are shown in this paper to be
modifications of the epipharynx (Fig. 524 and 528). The apodemes
of the muscids (Fig. 304, 308, and others) have been called mandibular
tendons by MacCloskie and others. This is incorrect as shown by the
figures and in the discussion of the maxillae. A number of workers
(e.g., Wesche, 1909) believe that the mandibles have united with the
labium and exist as chitinized strips on the cephalic aspect of the
labium or as thickenings on the meson of the theca. Neither of these
interpretations can be accepted when one takes into consideration the
relative position of these so-called mandibles and the manner of devel-
opment of the proboscis of the Calyptratae. The chitinized thickenings
on the cephalic aspect of the labium are located caudad of the maxillae
and the hypopharynx. This does not agree with the position of the
mandibles of other insects. Furthermore, these thickenings are present
in Tabanus where true mandibles occur. The chitinized thickenings
on the meson of the theca in some of the Diptera can not be considered
as rudiments of mandibles for many reasons. The most conclusive
objection to this interpretation lies in the fact that these thickenings
are very prominent in Simulium which has distinct mandibles in both
sexes.

When interpreting mouth-appendages, it is always necessary to
take into consideration the generalized relationship between the mouth-
parts and their association with the invaginations of the tentorium.
It is also very desirable to observe a large series of forms before attempt-
ing to homologize the parts. The above interpretations were apparently
not made from either of these vantage-points.

Maxillae. — All Diptera having functional mouth-parts have max-
illae. They are, however, greatly reduced and modified in some genera,
and at first glance bear little or no relation to the structure or location

207] HEAD OF DIPTERA — PETERSON ^7

of the maxillae of generalized Diptera or other insects. Numerous
intermediate stages of maxillary development are present in the various
species; consequently it is possible, and in fact comparatively easy, to
trace thruout the order the main line of specialization and several side
lines.

The hypothetical maxillae of the Diptera (Fig. 257) resemble the
maxillae of a generalized insect in their homologous sclerites, their posi-
tion between the mandibles and the labium, and their close association
with the invaginations of the posterior arms of the tentorium. Struc-
turally they are composed of small triangular cardines (ca), long
stipites (st), five-segmented palpi (mx.pl), needle-like galeae (g), and
short laciniae (la). The cardines and stipites differ from those of gen-
eralized insects in that they are embedded in the mesal membranous
area ventrad of the occipital foramen. The palpi, galeae, and laciniae
are free appendages. The proximal ends of the cardines are adjacent
to the invaginations of the posterior arms of the tentorium. The struc-
ture and position of the various parts of the hypothetical type have
been traced thruout the order. The species in which the ptilinum is
wanting are considered first.

The cardines (ca) are small distinct triangular selerites in Trichoc-
era (Fig, 260), Khyphus (Fig. 261), Dixa (Fig. 262), and the female
of Tabanus (Fig. 259). In these genera they are adjacent to the invagi-
nations of the posterior arms of the tentorium. The cardines of Simu-
lium (Fig. 258), in both males and females, differ from those of the
above genera in that they are large and occupy nearly all of the mem-
branous area between the postgenae dorsad of the stipites. Their
margins are also somewhat indistinct. No other forms figured have
distinct sclerites that are homologous with the cardines of the hypo-
thetical type. The maxillae of Rhabdophaga (Fig. 268), Bibiocephala
(Fig. 269), and Chironomus (Fig. 270) connect with the invaginations
of the posterior arms by means of narrow chitinized processes which
arise from the stipites proper. Undoubtedly these pieces are reduced
cardines which have lost the suture that separates them from the
stipites. The presence of this suture is suggested hy the suture-like
depression in the male of Bibiocephala (Fig. 76). Excepting Proraachus
.(Fig. 276) and the above forms, the cardo is wanting in all the maxillae
figured. The maxillae of Psychoda (Fig. 263) and Sciara (Fig. 267)
closely resemble some of the above maxillae, but the cardines as chi-
tinized pieces are apparently wanting. There is a distinct membranous
area between the proximal ends of the stipites and the invaginations
of the posterior arms of the tentorium. From forms such as these it is
concluded that the cardines have been lost as chitinized areas. No
other interpretation seems possible with the evidence at hand.

38 ILLINOIS BIOLOGICAL MONOGRAPHS [208

The stipites (st) are of various shapes and sizes as can be seen in
the figures. In Ehabdophaga (Fig. 268), Bibiocephala (Fig. 269),
Chironomus (Fig. 270), and possibly Myeetobia (Fig. 90), they have
united to form a chitinized strip or plate in the membranous area dorsad
of the labium. This piece should not be confused with the submentum
of the labium. In all species in which the postgenae have not united
ventrad of the occipital foramen, the proximal ends of the stipites are
near the invaginations of the posterior arms of the tentorium. In all
species where the postgenae form a continuous plate, the stipites are
reduced in size and situated at or beyond the ventral margin of the
head, as in Mydas (Fig. 319) and Eristalis (Fig. 328). In other words,
the usual association between the maxillae and the invaginations of the
posterior arms has been lost. Psilocephala (Fig. 281) and Psorophora
(Fig. 96) are exceptions to the last statement. In Psilocephala chi-
tinized thickenings (ch. th) are present on the ental surface of the
postgenae ventrad of the occipital foramen, and these are undoubtedly
rudiments of the stipites. The stipites of Psorophora (Fig. 266 and
96) are long, free rod-like structures located entad of the postgenae.
They extend between the occipital foramen and the ventral margin of
the head. The stipites of Geranomyia (Fig. 382) and Limnobia (Fig.
386) are also entad of the postgenae. In these genera their proximal
ends are united and they have no connection with the head-capsule.
The stipites of Tipula (Fig. 277) resemble those of Geranomyia and
Limnobia, but there is greater reduction in size, and they are completely
united along their mesal margins, thus forming a single median piece. '

The maxillae of Promachus (Fig. 84) differ from those of all other
genera in that the stipites and the cardines are united on the meson
and continuous with the postgenae near the occipital foramen. Narrow
membranous areas separate the maxillae from the postgenae near the
ventral margin of the head. This unique modification of the maxillae
agrees with the striking modifications in the other mouth-parts.

The figures show the variations in other genera belonging to this
group. In general it can be said that the stipites have been modified
by reduction and by removal to the ventral margin of the head and in
some cases are even located on the basiproboscis.

The maxillary palpi (mx. pi) of the Nematocera figured have from
two segments — Geranomyia (Fig. 382) and the female of Psorophora
(Fig. 266) — to five segments. The usual number is four or five. In
the Brachycera only one articulating segment is present. This segment
in Tabanus (Fig. 259) connects with an elongated portion of the stipes
which is called the palpifer by some. In this study the palpifer is
considered as wanting, since no palpus of the Diptera possesses over

209] HEAD OF DIPTERA— PETERSON 39

five segments and furthermore no piece is present at the base of any
generalized palpus which can be homologized with the palpifer of gen-
eralized insects. The greatest reduction in the palpus of the Nematocera
occurs in Geranomyia (Fig. 382), while in the Brachycera the palpus
of Mydas (Fig, 271) is a mere lobe.

A small finger-like structure arises from the ventro-mesal margin
of each stipes and projects mesad to the caudal aspect of the hypo-
pharynx in Tabanus (Fig. 259) and Simulium (Fig. 258). These pieces
are apparently homologous with the laciniae (la) of generalized insects.
The distal ends of these projections articulate against the caudal aspect
of the hypopharynx (Fig. 496 and 497), and in this respect they differ
from the laciniae of generalized insects. These pieces in Tabanus have
been described as laciniae by Patton and Cragg (1913).

A distinct lobe is present mesad of the palpus in the majority of
the Diptera that do not have a ptilinum. This structure is unquestion-
ably the galea (g), for in specialized insects which possess a distinct
galea the lacinia is generally reduced in size and in some cases wanting.
This tendency of development prevails in the Diptera. If the above
pieces in Tabanus and Simulium which are described as laciniae are
truly such, there can be no question regarding this interpretation of
the lobe adjacent to the palpus. The galeae vary considerably in size
and shape. They are long and needle-like in Tabanus (Fig. 259), in
the female of Psorophora (Fig. 266), and in Empis (Fig. 274), Exo-
prosopa (Fig. 285), and Eulonchus (Fig. 284a); while in Trichocera
(Fig. 260), Dixa (Fig. 262), Sciara (Fig. 267), Bittacomorpha, Chi-
ronomus (Fig. 270), Lonchoptera (Fig. 280), Scenopinus (Fig. 282),
and the male of Psorophora (Fig. 266) they are greatly reduced. In
Bibio (Fig. 264) and Geranomyia (Fig. 382) they are mere rudiments.
They are wanting in Ehabdophaga (Fig. 268), Tipula (Fig. 277),
Helobia (Fig. 385), Aphiochaeta (Fig. 278), Pipunculus (Fig. 279),
Platypeza (Fig. 272), and Dolichopus (Fig. 284).

The development of the maxillae of the genera possessing a ptilinum
will now be considered. No cardines or laciniae are present in this
group. The maxillary palpi are one-segmented and are present in all
forms except Conops (Fig. 305). The palpi interpreted liere as maxil-
lary palpi have been called labial palpi by some (e.g., Wesche, 1909).
The stipites and galeae are present in all the species studied, and they
undergo decided morphological changes. All connection or association
between the maxillae and the invaginations of the posterior arms of the
tentorium has been lost. This loss is even more pronounced than in
the Brachycera, since in all but a few species figured the maxillae are
far removed from the head and situated near the distal end of the

40 ILLINOIS BIOLOGICAL MONOGRAPHS [210

well-developed basiproboscis. This migration of the maxillae in the
Cyclorrhapha has not altered their generalized position between the
labrum-epipharynx and the labium.

The stipites of genera having a ptilinum show all stages of in-
growth from a turned-in free edge or end (st-e), to forms- in which it
is entirely entad of the membrane of the basiproboscis, as in Musca.
Eristalis (Fig. 286), Eulonchus (Fig. 284a), and Exoprosopa (Fig.
285) are the only forms without a ptilinum which show an ental growth
of the stipites. These genera make a good starting point for explaining
the characteristic development found in the Acalyptratae and the Calyp-
tratae. The following scheme of lines and dots has been adopted on
the drawings in order to show the degree of ingrowth of the stipes. A
continuous solid line on the stipes indicates a definite ectal boundary
which connects with the membrane of the basiproboscis. A broken line
indicates an ental edge or end which is free of the membrane between
it and the observer. The membrane is represented by stippling. For
convenience of description and homology the following division of the
stipes has been made : st represents the ectal portion of the stipes and
st-e the ental portion; and st is further divided into st-1 and st-2 as
seen in Coelopa (Fig. 288).

In Exoprosopa (Fig. 285) and Eulonchus (Fig. 284a) the proximal
end of the stipes is free and entad of the membrane, while the cephalic
edge and the dorsal end are entad in Eristalis (Fig. 286). From a form
similar to Eristalis it is possible to develop a stipes which would resem-
ble that of Sepsis (Fig. 287), Coelopa (Fig. 288), and Calobata (Fig.
296). In Sepsis the palpus is greatly reduced, but it connects with an
ectal portion of the stipes (st) which in turn gives rise to the free ental
portion (st-e). The free ental part extends ventrad and is continuous
with the galea, which emerges from the membrane near the base of the
labrum as a free appendage. The stipes of Coelopa (Fig. 288), Sapro-
myza (Fig. 289), and Sphyracephala (Fig. 293) is similar to that of
Sepsis, but in these forms the palpus arises from the cephalic margin
of the basiproboscis. The palpus is connected with the stipes proper
by means of a long chitinized strip (st-1) which is usually covered with
setae. This ectal portion of the stipes (st-1) is present in all but a few
genera, such as Chloropisca (Fig. 306), Heteroneura (Fig. 298), Chyro-
mya (Fig. 299), Loxocera (Fig. 300), and Euaresta (Fig. 292). In
a number of forms, particularly in the Calyptratae, a small chitinized
area is present ventrad of the palpus. This is regarded as a secondary
chitinization. The ectal portion of the stipes (st-2) is present in a
majority of the Acalyptratae and in one or two of the Calyptratae.

The ental portion of the stipes (st-e) is always present in the
members of this group. In Desmometopa (Fig. 303), Chloropisca (Fig..

211] HEAD OF DIPTERA— PETERSON 41

306), Conops (Fig. 305), and the Calyptratae it has no connection with
the ectal portion of the stipes (st-2) or the membrane, and by many
writers is commonly called the apodeme. The free so-called apodeme
is unquestionably derived from the ental ingrowth of the stipes, as
illustrated by the modifications found in the following genera : Coelopa
(Fig. 288), Sapromyza (Fig. 289), Tetanocera (Fig. 297), Arehytas
(Fig. 309), Musca (Fig. 304), and others.

The development of the galea (g) may be traced thruout the Cy-
clorrhapha in a manner similar to that of the stipes. In Eristalis
(Fig. 286) the galea is a long free appendage arising from the ventral
end of the stipes near the proximal end of the labrum-epipharynx. Its
length and size are greatly reduced in Sepsis (Fig. 287), but its position
is identical with that of Eristalis. Thruout the majority of the Acalyp-
tratae the position of the galea resembles that of Sepsis. Its size and
form undergo some change, as can be seen in the figures. In the Calyp-
tratae and some of the Acalyptratae the galea articulates with the
proximal end of the labrum and is more or less firmly connected with
the same. The ectal exposure of the galea is very small in these forms.
The large galea of the Acalyptratae has been considered as the maxillary
palpus by Wesche (1902). This interpretation is highly improbable.

LaMum. — The labium is the most specialized and characteristic
appendage of the mouth of Diptera. Its structural modifications are
very striking among the specialized genera, such as the Cyelorrhapha.
These modifications are largely due to the reduction of the parts and
the excessive development of membranous areas, and they agree with
similar types of modification in other head- and mouth-parts.

To explain the unique development of the labium of Diptera, it
has been necessary to make a critical study of the generalized condition
of this appendage as it occurs in the Nematocera and to compare it
carefully with the labia of more generalized insects. As is well known,
the labium of a generalized insect is the posterior, independent, flap-
like mouth-part, made up of a submentum, mentum, and ligula. The
ligula is further divided into palpigers, palpi, paraglossae, and glossae.
The labium of a generalized dipteron resembles that of a generalized
insect in its caudal position and in its independent condition, but it is
very different in structure. It is more or less enlarged and not flat
and flap-like, and the palpi and palpigers are always wanting, so far
as observed. Since the position of the palpi and the palpigers is very
useful in orienting the sclerites of the labium of generalized insects,
their absence in Diptera makes it exceedingly difficult to homologize cor-
rectly and locate the submentum, mentum, and the parts of the ligula.
The membranous condition of the labium also adds to this difficulty.

42 ILLINOIS BIOLOGICAL MONOGRAPHS [212

In order to get some light on this problem, a study was made of
the labium, particularly the submeutum and mentum, of a number of
generalized insects of the more common orders. The literature of this
subject was examined, but no satisfactory results were obtained from
this source. After a careful study of a number of labia, the following
general characteristics which bear upon the labium of Diptera, were
noted. The submentum is the large proximal segment, while the mentum
is usually small and in some cases very thinly chitinized and almost
obsolete. The sutures separating the mentum from the submentum
and the ligula are only represented by small remnants in Melanoplus.
The ligula, so far as observed, comprises the movable parts of the labium,
while the mentum and submentum are more or less firmly united with
the head-capsule. The proximal part of the ligula is usually well de-
veloped and gives rise to the palpigers, palpi, paraglossae, and glossae.
The glossae are located between the paraglossae, and in a number of
forms a distinct depression or thickening extends proximad between the
glossae and the proximal margin of the ligula.

"With these observations as a basis for comparison, the labium of
such generalized Diptera as Chironomus (Fig. 371), Simulium (Fig,
366), Trichocera (Fig. 365), Dixa (Fig. 375), and others may be inter-
preted as follows. The mesal membranous area of the caudal aspect
of the head, which is bounded by the postgenae (po), the occipital
foramen (o. f), and the proximal chitinized piece of the labium (the),
is made up of the submentum, mentum (su. me), and the cardines (ca)
and stipites (st) of the maxillae (mx). Since this area is largely mem-
branous, it is impossible to determine the boundaries of these sclerites.
The areas laterad of the cardines and the stipites apparently belong to
the maxillae, while the area mesad of these parts is made up of the
submentum and mentum (su. me). The important feature concerning
this mesal membranous area is the fact that the maxillae and the
labium both play a part in its formation. This undoubtedly indicates
that the submentum and mentum, of a more or less fixed nature in
generalized insects, have been more extensively fixed in the Diptera,
and that the submentum and mentum are included in the membrane
developed from the stipites and cardines. Such an interpretation is
altogether possible, since the proximal portions of the maxillae are adja-
cent to the submentum and mentum in generalized insects.

The ligula (Ig) of the generalized Diptera agrees with the ligula
of generalized insects in that it is the movable part of the labium.
Structurally it is composed of a well-developed proximal area which
gives rise to two large bulb-like paraglossae (pgl) and to two small

213] HEAD OF DIPTERA — PETERSON 43

membranous glossae (gl) which are located between the paraglossae.
The palpigers and labial palpi are wanting, but if in the future some
form is discovered wiiich shows these structures, they will undoubtedly
be found on the area here described as the ligula. The proximal portion
of the ligula has a decided furrow or thickening on its caudal aspect
along the meson. This thickening is characteristic of a number of
Diptera and resembles the proximal portion of the ligula of a number
of generalized insects. This mesal thickening marks the line of fusion
of the two parts of the labium during embryonic development.

The above interpretation of the labium is on the whole very satis-
factory for the numerous modified types found in the various families
of the Diptera, and with this interpretation it is possible to formulate a
hypothetical labium. This has been done in this study; but there have
been added to this labium the early stages of development of the more
important secondary structures wiiich are characteristic of the labia of
Diptera. It will therefore be advisable to call such a hypothetical labium
a typical labium in order to distinguish it from the true hypothetical
type of other parts of this study.

A typical labium of the Diptera (Fig. 1, 73, 140, 362, and 363) is
made up of a submentum, mentum, and ligula. The submentum
and mentum (su. me) are firmly united with the head and constitute
the greater portion of the mesal membranous area of the caudal aspect
of the head. The ligula (Ig) is the large swollen and movable portion
of the labium and consists of the mediproboscis (mpr) and the disti-
proboscis (dpr). The mediproboscis has a chitinized area on its caudal
aspect which is commonly called the theca (the). The distiproboscis is
composed of two large membranous bulb-like paraglossae (pgl) and two
small membranous glossae (gl) which are located between the proximal
parts of the paraglossae. The important and characteristic features of
a typical labium are the chitinized pieces on the caudal and lateral as-
pects of the paraglossae and the trachea-like structures on the mesal
aspects. The details of the various parts will be more fully discussed
as each part is considered and its modification traced thruout the order.

The submentum and mentum (su. me) are present as a membranous
area in a majority of the Nematocera and in the females of Tabanus
(Fig. 74). This area undergoes considerable modification, as was seen
in the discussion of the maxillae and postgenae, and is illustrated by
the figures. Rhyphus (Fig. 80 and 374) is apparently the only genus
which has within this area a chitinization which can not be considered
as a modification of the maxillae or of the postgenae. This piece is a
more or less distinctly chitinized, inverted-flask-shaped area between
the maxillae. If this is a primary chitinization, it is probably a rem-

44 ILLINOIS BIOLOGICAL MONOGRAPHS [214

nant of the submentum. A similarly situated area found in Mycetobia
has been homologized by some writers with that of Rhyphus. This
interpretation is undoubtedly incorrect, since this area in Mycetobia
(Fig. 90) gives rise to chitinized projections at its ventro-lateral angles
and these in turn connect with the maxillary palpi and the galeae.
Furthermore, the relationship which this piece bears to the proximal
end of the theca (the) would tend to disprove such an interpretation.
This piece in Mycetobia is undoubtedly a specialization of the maxillae
similar to the modifications found in Bibiocephala (Fig. 83) and Rhab-
dophaga (Fig. 86). In all genera where the postgenae have grown
together on the meson the submentum and mentum have been elimi-
nated, unless one regards the area between the ventral margin of the
head and the theca as derived from these areas. This area, as already
described for the Cyclorrhapha, is very extensive and forms the caudal
portion of the basiproboscis (bpr).

The proximal portion of the ligula or mediproboscis (mpr) of the
typical labium is largely membranous, but it has on its caudal aspect
a distinctly chitinized area, the theca (the), which has a distinct furrow
on its meson. The shape, size, and degree of chitinization of the theca
vary greatly, as can be seen in Bibio (Fig. 364), Trichocera (Fig.
365), Rhyphus (Fig. 374), Promachus (Fig. 376), Tabanus (Fig. 391),
Chyromya (Fig. 411), Conops (Fig. 420), Rhamphomyia (Fig. 424), and
Musca (Fig. 466). There is a distinct furrow or thickening on the
meson of the majority of the Nematocera and the Brachycera, and rem-
nants of these thickenings occur also among the Cyclorrhapha. In some
of the Diptera the structural condition of the meson has a marked influ-
ence on the shape of the dorsal and ventral margins of the theca. The
cephalic aspect of the proximal portion of the ligula of a typical labium
is concave and membranous and connects with the proximal part of the
lance-like portion of the hypopharynx. In the Nematocera the cephalic
aspect resembles the typical labium, and in the Brachycera and in a
majority of the Cyclorrhapha it has a distinctly chitinized groove. This
is well illustrated by Tabanus (Fig. 392), Eristalis (Fig. 441), and a
majority of the Calyptratae. The degree of chitinization varies con-
siderably, and in some forms heavy, chitinized, cord-like pieces extend
along the sides of the groove from the glossae to the proximal end of
the labium.

The distiproboscis of the typical labium is composed of two large
independent, highly membranous, bulb-like paraglossae (pgl), usually
called oral lobes or labellae, and two small membranous glossae (gl).
Each paraglossa has on its lateral and caudal aspects a Y-shaped chi-
tinized support which has been commonly called the furca. For con-

215] HEAD OF DIPTERA— PETERSON 45

venience in description and as an aid in tracing the development of the
parts of the furca thruout the order, it has been divided into furca-1,
which is the stem of the Y, furca-2, which is the dorsal arm of the Y,
and furea-3, which is the ventral arm. The furca articulates with a
small sclerite which is located between the proximal end of furca-1 and
the distal end of the chitinized furrow on the meson of the theca. This
piece has been called the sigma (si). Another small, independent
sclerite is located in the membrane just laterad of the sigma and this
may be known as kappa (k). Each paraglossa has on its mesal aspect
two trachea-like structures which arise from the proximal portion of
the glossa. These structures are commonly called pseudotracheae (ps).
A general survey of the characteristics of the paraglossae of the
various labia shows that they are usually bulb-like, membranous, and
somewhat flexible. In these respects they differ decidedly from the
firmly chitinized, flap-like labia of many generalized insects. Their size
and shape vary greatly, as can be seen in Bibio (Fig. 364), Leia (Fig.
368), Promachus (Fig. 376), Geranomyia (Fig. 382), Tipula (Fig. 384),
Tabanus (Fig. 390), Conops (Fig. 417), Empis (Fig. 421), Siphona
(Fig. 458), Musca (Fig. 467), Stomoxys (Fig. 479), and Olfersia (Fig.
488). The use to which the labia are put seems to have some influence
on their form. The main line of development thruout the genera figured
is toward the type found among the Calyptratae, in which the labia
are usually large, decidedly membranous, and joined together on the
dorso-caudal areas, as in Hydrotaea (Fig. 475), Sarcophaga (Fig. 477),
Sepsis (Fig. 439), Loxocera (Fig. 461), Tetanocera (Fig. 463), and
many other genera.

The membranous development of the paraglossae is not always a
good indication of the main line of specialization. In a number of
scattered genera, Chironomus, Rliyphus, Aphiochaeta, Chloropisca,
Platypeza, Leptis, Psilocephala, and Lonchoptera, it is next to impossi-
ble to make out the chitinized pieces, such as kappa, sigma, and furca,
because of the membranous condition of the entire labium. Outside of
the above-named forms, the chitinized pieces of the paraglossae are
usually distinct when present. These supports may be secondary in
origin or they may be remnants of former chitinized parts of the para-
glossae. It is possible to show how the various chitinized pieces of the
majority of the labia may have been developed from the typical form.

The sclerite designated as kappa (k) on the typical labium is only
present in Tabanus (Fig. 390 and 391), Tipula (Fig. 388), and Bitta-
comorpha (Fig. 85). No other dipteron gives any evidence whatever
of such a sclerite. In the above-mentioned genera the pieces are em-
bedded in the membrane laterad of the ventral ends of the theca. Some

46 ILLINOIS BIOLOGICAL MONOGRAPHS [216

one has iuterpreted these pieces as rudimentary palpigers or palpi. This
may or may not be correct. It is possible for palpi to be in such a
position ; but since no other genera have similar pieces, and since they
are so decidedly dissimilar to the labial palpi and palpigers of general-
ized insects, they are here regarded as secondary sclerites.

The sclerite designated as sigma (si) is present as a chitinized thick-
ening at the ventral end of the theca, as in Eristalis (Fig. 443), or as
a distinct piece, as in a majority of the Brachycera and the Cyclorrha-
jDha. In all genera it is situated between the ventral margin of the
theca and the furca. Only a few genera of the Nematocera, such as
Tipula (Fig. 388) and Psorophora (Fig. 380), have these sclerites. They
undergo some modification in size and structure as can be seen in the
following genera: Tabanus (Fig. 391), Mydas (Fig. 397), Conops (Fig.
418), Borborus (Fig. 437), Eristalis (Fig. 443), Coelopa (Fig. 448),
and Scatophaga (Fig. 470).

The furca of Bibio (Fig. 315) and that of Tabanus (Fig. 317)
closely resemble the typical form. In Bibio, furca-1 (f-1) and furea-2
(f-2) are one continuous piece, while furca-3 (f-3) is a distinct arm.
In Tabanus, furca-2 and furca-3 are distinctly chitinized areas arising
from the distal end of furca-1. Only one chitinized support is present
in Sciara (Fig. 314), Ehabdophaga (Fig. 313), Psychoda (Fig. 318),
Stratiomyia (Fig. 331), and Trichocera (Fig. 311). In Trichocera this
support has a decided dorsal bend near the constriction of the para-
glossae. This bend is also present in Psychoda and Stratiomyia, but
the constriction is wanting. The distal portion of the furca beyond the
bend is homologous with furca-2, and furca-3 is wanting in these forms.
Furca-2 is present and furca-3 is wanting in Scenopinus (Fig. 325) ;
furca-3, however, is present in more species than furca-2. Such is the
case with Borborus (Fig. 342), Chrysomyza (Fig. 341), Coelopa (Fig.
337), Tetanocera (Fig. 344), Scatophaga (Fig. 357), Musca (Fig. 351),
and Thelaira (Fig. 346).

Furca-1 (f-1) varies considerably thruout the order. In general-
ized forms where the dorso-caudal portions of the paraglossae are not
joined together the furcae are always well separated. They are also
separated in some forms where the paraglossae are joined, as in Mydas
(Fig. 397) and Eristalis (Fig. 443). In Chyromya (Fig. 411), Dro-
sophila (Fig. 454), Tetanocera (Fig. 463), and Sepsis (Fig. 439), an
intermediate piece joins the mesal ends of furcae-1 while in Sarcophaga
(Fig. 477), Musca (Fig. 466), Coelopa (Fig. 448), Sapromyza (Fig.
409), Chrysomj^za (Fig. 457), Heteroueura (Fig. 459), and Oecothea
(Fig. 452) furcae-1 are united and form one continuous U-shaped piece.
This type of furcae is present among the Calyptratae. The furcae of

217] HEAD OF DIPTERA — PETERSON A7

specialized forms, such as Olfersia (Fig. 488), Conops (Fig. 418),
Siphona (Fig. 355), Empis (Fig. 421), and others, are not differen-
tiated, since the greater part of the lateral aspects of the paraglossae is.
chitinized.

In the typical labium two simple trachea-like structures, commonly-
known as pseudotracheae (ps), arise from the proximal part of each
glossa and extend onto the mesal membranous aspect of each paraglossa.
These trachea-like structures are in reality small chitinized troughs,
which serve as conduits for the liquid food. Pseudotracheae are unique-
structures and peculiar to Diptera, so far as known. They are present
in only a few generalized forms, but from these genera it is possible
to develop the pseudotracheal arrangement and structure of the more
specialized Diptera. It is consequently assumed that the pseudotracheae
have probably arisen only once within the order, and that this happened
some time after the group as a whole was set off as a distinct order.

The psedotracheae (ps) of Tipula (Fig. 383) resemble those of the
typical labium in that the two main pseudotracheae arise from each
glossa and extend over the mesal membranous area of the paraglossa,
one of the pseudotracheae extending caudad and the other cephalad.
These ducts are secondarily branched and resemble a fern. The pseudo-
tracheae of Mycetophila (Fig. 11) and Leia (Fig. 368) are reduced and
only the caudal pseudotracheae extend over the paraglossae. The para-
glossae in these genera are united along the meson and form a single
large lobe. The cephalic pseudotracheae are indicated by small rudiments
in Mycetophila (Fig. 11). The pseudotracheae in these forms resemble
the typical labium in that they are simple, unbranched, chitinized
troughs. From the typical labium, or from the pseudotracheae as they
occur in Tipula, it is possible to derive the arrangement and structure
of the pseudotracheae as they are found in Tabanus (Fig. 390) and
similar forms, where two long pseudotracheal trunks (m. ps) extend
cephalad and caudad from the glossae (gl) and give rise to many
branches on their ventral side. These branches extend ventrad over
the entire mesal area of the paraglossa (pgl). The arrangement of the
pseudotracheae of most Diptera is readily derived from a form similar
to Tabanus. The arrangement in Scenopinus (Fig. 400), Psiloeephala
(Fig. 403), and many of the Calyptratae resembles that in Tabanus.
In such genera as Stratiomyia (Fig. 396), Oecothea (Fig. 453), Coelopa
(Fig. 449), and Heteroneura (Fig. 460) no main collecting ducts
(m. ps) extend beyond the glossae. In many genera, such as Chloro-
pisca (Fig. 431) and Chyromya (Fig. 412), no line of demarkation
can be drawn between the proximal ends of the pseudotracheae and the
glossae.

48 ILLINOIS BIOLOGICAL MONOGRAPHS [218

U-shaped or open ring-like thickenings are present in the pseudo-
tracheae of the more specialized Diptera. They do not occur in the
simple pseudotracheae of Mycetophila or in some of the highly special-
ized forms. The histological structure of a pseudotrachea has been
clearly demonstrated by several workers. According to Dimmock, "The
pseudotracheae on the inner surfaces of the labellae of Musca are cylin-
drical channels, sunk more or less deeply into the surfaces of the labellae
according to the amount that that surface is inflated, and they open on
the surface in zig-zag slits. These channels are held open by partial
rings, more strongly chitinized than the rest of the membrane of the
cylinder. As seen from above in Musca, [Fig. 485], the pseudotracheae
appear to be supported by partial rings, one end of each of which is

forked The pseudotracheae of Eristalis are so nearly like

those of Musca [Calliphora] vomitoria that I have not figured those
of the former." All my observations of the histological structure of
pseudotracheae agree with those made by Dimmock. Tho no attempt
was made to work out the detail of the histological structure in the
various genera studied, a number of interesting facts were observed.
The chitinized, taenidia-like thickenings (ps. th) in Ochthera (Fig. 445
and 483) are large U-shaped structures which are partially embedded
in the membrane. The ends of these thickenings project considerably
beyond the surface of the membrane and resemble these structures in
Bombylius major (Fig. 482), as figured by Dimmock. The pseudo-
Iracheae of Calobata (Fig, 446) have developed into rows of small chi-
tinized teeth (tee).

The pseudotracheal area of the paraglossae undergoes its greatest
specialization in forms in which the paraglossae assume a biting func-
tion. This biting type is brought about by the development of distinct
chitinized teeth arising between the proximal ends of the pseudotracheae.
Rudimentary or well-developed teeth occur in Musca (Fig. 467), Sar-
cophaga (Fig. 478), Scatophaga (Fig. 472), Lispa (Fig. 481), and
Stomoxys (Fig. 480). In Musca the small, chitinized, so-called pre-
stomal teeth (tee) are present between the proximal ends of the pseudo-
tracheae. In Scatophaga and Lispa these teeth are large and distinct.
Their greatest development occurs in Stomoxys, and so far as observed
pseudotracheae are wanting in this form. An extensive discussion of
the development and the structure of the chitinized teeth of the para-
glossae has been given by Patton and Cragg (1913).

The glossae (gl) of a typical labium (Fig. 1 and 73) are two small
lobes located between the proximal portions of the paraglossae distad
of the furrow on the theca and at the distal end of the cephalic groove.
Thruout the order the glossae are between the paraglossae and at the

219] HEAD OF DIPTERA— PETERSON 49

distal end of the cephalic groove. They are not well-defined structures
in all labia. In Chironomus (Fig. 371), they are two small membranous
lobes, while in Simulium (Fig. 366), Rhabdophaga (Fig. 367), Bibio
(Fig. 364), and Rhyphus (Fig. 374) they have the form of a single
median membranous lobe. The glossae of Simulium are of particular
interest since they have a great number of minute chitinized thickenings
which radiate from the proximal end. So far as known these thicken-
ings bear no relation to the psedotracheae of the paraglossae. The
glossae of Tabanus (Fig. 391) are united and form a chitinized triden-
tate piece with the median tooth the longest. The glossae of Lonchop-
tera (Fig. 407) illustrate a form intermediate between a median spine,
such as occurs in Psorophora (Fig. 381), Aphiochaeta (Fig. 393), Empis
(Fig. 422), and Exoprosopa (Fig. 426), and the U-shaped structure
characteristic of the Cyclorrhapha. The glossae of the Calyptratae re-
semble in general the glossae of Musca (Fig. 465). In the genera of
this group the cephalic ends of the U-shaped piece are free and project
cephalad from the point of attachment of the pseudotracheae. The
glossae are not well defined in a few genera, Sapromyza (Fig. 410),
Chyromya (Fig. 412), and Chloropisca (Fig. 431), for example, and
it is impossible to differentiate the glossae from the chitinized groove
of the mediproboscis and the proximal ends of the pseudotracheae. The
glossae of Promachus (Fig. 379) are specialized in that they give rise
to two thickenings which extend dorsad in the groove of the labium
and serve as guides for the hypopharynx and galeae.

EPIPHARYNX AND HYPOPHARYNX

The anterior end of the alimentary canal of the Orthoptera and
of insects in general is divided transversely into two parts, one forming
the cuticular lining of the clypeus and labrum and the other the lining
of the opposite side of the mouth cavity. The portion lining the clypeus
and labrum is known as the epipharynx (ep), and that of the opposite
side as the hypophar^aix (hp). Each lining may be subdivided into
several parts. These are of particular significance in a study of the
epipharynx, which has a distinct chitinized mesal piece, and two lateral
chitinized pieces which are situated near the clypeo-labral suture. These
lateral pieces, which have been designated as tormae (to), and, so far
as I know, are described here for the first time, project cephalad toward
the clypeo-labral suture in Melanoplus (Fig. 515) and Gryllus (Fig.
516) and connect with both the labrum and clypeus. In Gryllus they
are interpolated between the clypeus and the labrum and appear as
small triangular sclerites on the cephalic aspect. The tormae of Peri-
planeta (Fig. 514) are not as well developed as in the above-named

so ILLINOIS BIOLOGICAL MONOGRAPHS [220

genera, but they are present and project toward the cephalo-lateral
corners of the labrum. The caudal end of the epipharynx in many in-
sects gives rise to long chitinized arms which have been called cornua
(cu). The hypopharynx may be subdivided into a distal, unpaired, me-
dian piece, which is usually called the hypopharynx, and a proximal
paired area.

The chitinized portion of the anterior end of the alimentary canal
of Diptera can be homologized with the epipharynx and the hypophar-
ynx of generalized insects. The following hypothetical epipharynx
and hypopharynx (Fig. 493) and their closely associated parts have
been constructed for Diptera. In the figures of the lateral views of the
hypothetical type an enlarged, three-sided, chitinized tube extends cau-
dad from the dorsal end of the hypopharynx and epipharynx. It has
been called the oesophageal pump (oe. p). This is not a part of the
epipharynx or of the hypopharynx, but is a modification of the pharynx,
a portion of the alimentary canal. All of the chitinized parts ventrad
of the membranous area at the cephalic end of the oesophageal pump
belong to the epipharynx and the hypopharynx. The dorsal ends of
the epipharynx and the hypopharynx are united and form a single chi-
tinized tube, and this has been called the basipharynx (bph). Except
for this union, the epipharynx and the hypopharynx are continuous
chitinized pieces with lance-like distal ends. The distal portion of the
epipharynx is joined to the labrum by a membrane along its lateral
margin. The tormae in the hypothetical type project from th'C lateral
margins of the epipharynx and unite with the latero-ventral portions
of the fronto-clypeus (fr. c). Two projections occur at the dorsal end
of the basipharynx, and these are considered homologous with the cor-
nua (cu) of the epipharynx of generalized insects. The distal end of
the hypopharynx is a free lance-like organ, and a salivary duct (s. d)
enters its proximal end just dorsad of the place where it joins the
labium (li). The salivary duct extends thru the hypopharynx to its
distal end.

The oesophageal pump of the alimentary canal is closely associated
with the epipharynx and hypopharynx in all the Nematocera and in
Promachus (Fig. 517), Tabanus (Fig. 494), Leptis (Fig. 520), and
Psilocephala (Fig. 533) of the Brachycera. In a majority of the above
forms, the oesophageal pump is an elastic, semi-chitinized, three-sided
tube with muscles connecting with each of its surfaces. A contraction
of these muscles expands the tube, which upon their relaxation assumes
its normal shape. In some forms, as Tabanus and Promachus, there
is only one chitinized elastic surface. In a number of genera, as Chi-
ronomus (Fig. 531), Psychoda (Fig. 529), and Leptis (Fig. 520), the

221] HEAD OF DIPTERA— PETERSON 51

tube is more or less membranous and not distinctly three-sided. The
oesophageal pump is wanting in all the Diptera except those named,
and the membranous oesophagus connects directly with the basipharynx.
The oesophageal pump shows considerable variation in its shape, posi-
tion, and size, as can be seen in the figures of Bibio (Fig. 523), Rhyphus
(Fig. 508) and others.

The basipharynx (bph) is interpreted as including all of the united
portions of the epipharynx and the hypopharynx, but the extent of
this union varies somewhat in the different genera. In a majority of
the Nematocera no sutures or constrictions occur between the basiphar-
ynx and the lance-like portions of the epipharynx and the hypophar-
ynx. Such constrictions and secondary sutures do occur in a majority
of the Brachycera, as in Leptis (Fig. 520) and Promachus (Fig. 517),
and in all of the Cyclorrhapha. The basipharynx (bph) varies in size
and shape, as can be seen in the figures. Muscles connect with the
cephalic and caudal aspects of the basipharynx, those on the cephalic
aspect expanding the basipharynx and thus producing suction. This
sucking apparatus is well developed in all forms which have no oesophag-
eal pump. The chitinized projections at the dorsal end of the basiphar-
ynx, called the cornua (cu), vary in shape and size. Some are blunt,
others long and narrow, as in Leptis and the Calyptratae, and still
others are disk-shaped, as in Promachus (Fig. 517).

Distinct tormae (to) are present in Diptera except in a few species
of the Nematocera. In all the Nematocera and in Leptis (Fig. 520),
Psilocephala (Fig. 533), Platypeza (Fig. 543), Aphiochaeta (Fig. 544),
Lonchoptera (Fig. 539), and Scenopinus (Fig. 538), they resemble the
hypothetical type in that they join with the fronto-clypeus. In other
genera the tormae have an exposed portion located ventrad of the
fronto-clypeus and all connection between the fronto-clypeus and the
tormae is lost, except in Simulium (Fig. 497) and Tabanus. The
variations in the shape and the extent of the tormae is well illustrated
by the numerous figures. The so-called fulcrum described by numerous
morphologists for the Calyptratae is composed of the tormae and the
basipharynx. A more or less distinct secondary suture (s. s) is shown
in the drawings as separating the tormae from the basipharynx, and
the broken line on the tormae indicates the place of connection of the
membrane of the basiproboscis with the tormae. In figures of the
Nematocera and of forms in which the tormae connect with the fronto-
clypeus the broken line indicates the place of union between these parts.

The epipharynx (ep) is present and closely associated with the
labrum in all Diptera having functional mouth-parts. The interrela-
tionship between the epipharynx and the labrum has been discussed

52 ILLINOIS BIOLOGICAL MONOGRAPHS [222

under the heading labrum. The epipharynx in a number of generalized
Diptera, such as Tabanus (Fig. 494), Simulium (Fig. 497), Dixa (Fig.
501), Limnobia (Fig. 507), and Sciara (Fig. 513), resembles the hypo-
thetical type. In the majority of the Diptera it differs from the hypo-
thetical type in that it is completely separated from the basipharynx
by a constriction or a secondary suture. This hinge in the epipharynx
permits the proboscis to bend at this point when it is withdrawn into
the oral cavity. The lance-like portion of the epipharynx in the Calyp-
tratae and some other forms is completely separated from the basiphar-
ynx by the development of a special piece which is commonly called
the hyoid (hy). The lance-like portion of the hypopharynx also articu-
lates against the hyoid. The hyoid is a secondary sclerite which origi-
nated from the epipharynx or the hypopharynx and serves the purpose
of keeping open the alimentary canal, which passes thru it. A structure
similar to the hyoid of Musca (Fig. 600) is found in Stomoxys (Fig.
599 ) , where a large and strong trachea-like tube extends between the
dorsal ends of the lance-like portions of the epipharynx, the hypophar-
ynx, and the basipharynx.

In size and shape the epipharynx agrees more or less closely with
the labrum. The epipharynx in sucking Diptera is, as a rule, long and
needle-like, while in other forms it is usually short and blunt. In many
genera of the Acalyptratae it has a secondary transverse suture near its
distal end, as shown in Sepsis (Fig. 583) and Eristalis (Fig. 588).

A few genera show special modifications of the epipharynx. This
is particularly true of Dolichopus (Fig. 524 and 528). In this genus^
the epipharynx closely resembles the hypothetical type in the presence
of a distinct membrane between the labrum (1) and the epipharynx
(ep). The specialization of the epipharynx consists in the bifurcation
of its distal end and in the presence of a long club-shaped piece which
projects from its meson dorsad into the cavity formed by the basiphar-
jmx, the tormae, and the fronto-clypeus. These modifications are
peculiar to species of the Dolichopodidae. The bifurcations at the distal
end are of particular interest, since they have been interpreted as man-
dibles by Langhoffer (1888). They are much longer in some of the
genera of the family than in others. The lateral and caudal views of
the epipharynx and the hypopharynx of Dolichopus show clearly the
relation these projections have to the other parts, and justify the inter-
pretation here given.

The single, median, distal, lance-like portion of the hypopharynx
is present in all but a few of the genera studied. The cephalic portion
of the labium usually connects with the lance-like portion of the hy-
popharynx just ventrad of the point of entrance of the salivary duct.

223] HEAD OF DIPTERA— PETERSON 53

In a few cases, as in Borborus (Fig. 565 and 587), the hypopharynx is
completely fused with the labium, while in others, as in Euaresta (Fig.
572), it is nearly so. In a majority of the genera the secondary separa-
tion of the lance-like portion of the hypopharynx from the basipharynx
corresponds with the similar separation in the epipharynx. The shape
and size of the hypopharynx also vary considerably, as can be seen in
the figures. In mouth-parts fitted for sucking and piercing, the hy-
popharynx is usually long and needle-like ; while in licking forms (most
Calyptratae ) , it is greatly reduced.

The salivary duct (s. d) enters the proximal portion of the lance-
iike part of the hypopharynx and in most cases it is carried as a duct
or groove along the cephalic surface of that organ to the distal end.
The course of this duct or groove is indicated by broken lines in the
figiires of the caudal aspect of the hypopharynx. The salivary duct
before entering the hypopharynx is enlarged and bulb-like in many
species. In Tabanus (Fig. 494) the salivary bulb (s. b) is a chitinized
structure continuous with the hypopharynx, while in Promachus (Fig.
517) it is chitinized, but separated from the hypopharynx. A chitinized
bulb and an enlarged membranous swelling are both present in Dolicho-
pus (Fig. 528).

The peculiar epipharynx and hypopharynx of Olfersia (Fig. 606)
can be homologized with the more common types found thruout the
order. The principal difference is in the shape and position of the
basipharynx, the tormae, and the hyoid. The two lance-like structures
embedded in the deep membranous depression about the oral cavity
are the labrum-epipharynx and the lance-like part of the hypopharynx.
The long, crescent-shaped piece which extends cephalad from the proxi-
mal end of the labrum-epipharynx to the pear-shaped piece, is homolo-
gous with the hyoid (hy), and the pear-shaped piece with which the
hyoid connects is composed of the tormae (to) and the basipharynx
(bph). The exposed parts of the tormae in the membrane ventrad of
the head are very small in this genus.

Only rudiments of mouth-parts are found in the head of Gastrophi-
lus (Fig. 490 and 492). The anterior end of the alimentary canal is a
simple chitinized tube which leads to the small opening on the ventral
aspect of the head. This tube undoubtedly originated from the epiphar-
ynx and the hypopharynx. The mouth-parts are greatly reduced or
wanting. It is possible that the small bulb-like structures located
latero-caudad of the opening are remnants of the labium. It is impos-
sible to homologize the other minute modifications surrounding the
mouth-opening.

In the Cyrtidae, as Oncodes (Fig. 109, 486, and 487), the mouth-

54 ILLINOIS BIOLOGICAL MONOGRAPHS [224

parts show a greater reduction than in Gastrophilus, while in species
of Eulonchus (Fig. 364a) they are well developed. In Oncodes a chi-
tinized ring is present in the membrane which covers the oral cavity,
and a broad plate extends dorsad from its caudal margin, giving rise
to a small membranous tube, the oesophagus, which has no opening to
the exterior as far as could be determined. It is impossible to homolo-
gize the parts within the oral cavity. The ental plate which gives rise
to the oesophagus, may be homologous with the basal portion of the
epipharynx and the hypopharynx.

A general survey of the epipharynx and hypopharynx shows that
the relationship between these parts and the head-capsule corresponds
with the relationship between the mouth-parts and the head. Since the
epipharynx and the hypopharynx are always connected with the labrum
and the proximal part of the labium, they are projected ventrad when
the labrum and labium are extruded. The interrelation of the mouth-
parts and the epipharynx and hypopharynx is fixed, never changing thru-
out the order, no matter what specialization may take place. The espe-
cially striking feature of the epipharynx and the hpopharynx in various
genera which have functional mouth-parts, is the decided similarity of
the two thruout the order, as shown by the various figures. The parts
undergo secondary changes in their size and shape, but in no case where
the mouth-parts are functional is there an entire loss of a part, which,
however, happens in many cases with the mouth-appendages. The epi-
pharynx and hpopharynx of the Calyptratae in particular show a devel-
opment of joints, secondary sclerites, and membranous areas, which
permit a considerable amount of flexibility.

SUMMAEY

This investigation deals with the homology of all the sclerites of
the fixed and movable parts of the head of one or more representatives
of fifty-three of the fifty-nine families of the Diptera of North America
as listed by Aldrich. With this large series it has been possible to
make clear a number of little-understood relationships and structural
modifications in the head and mouth-parts, and also to point out their
homology with the corresponding parts and areas in insects of other
orders. The six hundred and more figures show the form and structure
of all the parts for each of the families studied.

Modifications of the fixed and movable parts usually take the form
of reduction, change of shape, loss of chitinization, or expansion of the
membranous areas. The different parts have been discussed separately,
and a hypothetical or typical form has been constructed for each part.

225] HEAD OF DIPTERA— PETERSON 55

One of the most important conclusions concerning the generalized
head-capsule relates to the position of the epicranial suture. The stem
of this suture along the dorso-meson represents the line of fusion of
the paired sclerites of the head, while the arms of the suture ventrad
of the antennal fossae enclose the unpaired sclerites of the head. This
suture resembles the epicranial suture in the immature stages and the
adult forms of all the generalized members of the more common orders.

Two unpaired sclerites, front and clypeus, are enclosed by the fork
of the epicranial suture, and in all but one or two genera form a con-
tinuous area called the fronto-clypeus.

The labrum is an unpaired, distinct, tongue-like structure situated
ventrad of the fronto-clypeus. It is joined to the epipharynx and the
resulting structure is known as the labrum-epipharynx.

The tormae are chitinized lateral pieces of the epipharynx which
project cephalad and unite with the fronto-clypeus in generalized Dip-
tera. They are also present in such generalized insects as the Orthop-
tera. In the more specialized Diptera the tormae are interpolated be-
tween the fronto-clypeus and the labrum, and in all but a few genera
lose all connection with the chitinized portions of the fronto-clypeus.
Their exposed surface is best seen from a cephalic view.

The crescent-shaped frontal suture dorsad of the antennal fossae
marks the line of invagination of the ptilinum. The origin of the
ptilinum has not been determined.

The vertex is the paired continuous area on the cephalic aspect of
the head, and the region of the vertex ventrad and mesad of each com-
pound eye is a gena.

The compound eyes are usually large and located on the cephalo-
lateral aspects of the head. They show secondary sexual characters in
a greater number of species than do any other of the fixed and movable
parts. The three ocelli are arranged in the form of a triangle and
located on the vertex dorsad of the bifurcation of the arms of the epi-
cranial suture.

The occiput and postgenae are continuous areas of the caudal sur-
face. The former occupies the dorsal portion and is secondarily modified
about the occipital foramen to form the parocciput. The postgenae are
the two areas of the ventral half, separated by a membrane in gener-
alized forms and united ventrad of the occipital foramen in all the
Brachycera and the Cyclorrhapha. They are also secondarily divided
into parapostgenae along the mesal membrane.

The tentorium of generalized Diptera is represented by the usual
three pairs of arms and a rudimentary body. It undergoes striking
modifications, and influences to a considerable extent the detailed struc-

56 ILLINOIS BIOLOGICAL MONOGRAPHS [226

ture of the head. The relation between the invaginations of the ten-
torium and the movable appendages of the mouth, which is so important
a feature of all generalized insects, is also characteristic of the members
of this order.

The development of the antennae from a generalized filiform type
to that found among the Cyclorrhapha can be traced on the figures.

Only a few generalized Diptera have mandibles. These are only
present in the females except in Simulium, in which they are well
developed in both sexes.

All Diptera having functional mouth-parts have maxillae. The
maxillae of generalized Diptera resemble the maxillae of generalized
insects except for the absence of palpifers and the fusion of the cardines
and stipites with the head-capsule. The maxillae undergo considerable
modification, and are reduced to a mere ental rod and a palpus in the
Calyptratae.

The labium is the most characteristic and specialized appendage of
the mouth, and shows modifications due to reduction and membranous
development. The palpigers and labial palpi are always wanting. The
submentum and mentum are represented by a membranous area of the
caudal surface of the head. The ligula, or the movable portion of the
labium, has a basal part which usually gives rise to two large bulb-like
paraglossae and to glossae situated between them. The paraglossae are
specialized, and have chitinized areas on their lateral and caudal sur-
faces and pseudotracheae on their mesal surface.

The parts of the epipharynx and the hypopharynx can be homolo-
gized with the corresponding parts in generalized insects. There is a
great similarity in the form of the epipharynx and hypopharynx of all
Diptera, which is especially striking when considered in connection with
the modifications that have taken place in all other parts.

The various mouth-parts show striking modifications thruout the
order, but all, including the epipharynx and the hypopharynx, retain
their relative positions, even tho they may be extruded from the head-
capsule for a considerable distance, as in some of the Calyptratae. The
proboscis of the Cyclorrhapha is composed of the labium, maxillae,
hypopharynx, labrum-epipharynx, and tormae. The paraglossae of the
labium form the large lobes, or labellae, at its distal end.

The mouth-parts of Oncodes and Gastrophilus are not functional,
and are so greatly reduced that it is difficult to homologize their parts^

227] HEAD OF DIPTERA— PETERSON 57

BIBLIOGRAPHY*

Becher, E.

1882. Zur Kenntnis der Mundtheile der Dipteren. Denkschr. k. Akad.
Wissensch., Wien, math.-natiirw. CI., 45:123-162; 4 pi.

1883. Zur Abwehr. Zool. Anz., 6:88-89.
Berlese, a.

1909. Gli Insetti loro organizzazione, sviluppo abitudini e rapporti coH'umo.,
I :i54-i59.
Blanch ARD^ E.

1850. De la Composition de la Bouche dans les Insectes de I'ordre des
Dipteres. Compt. rend. Acad. Sci. Paris, 31 :424-427.
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1880. Sur la Constitution de I'Armature Buccale des Tabanides. Bull, de
la Soc. Philom., 4, No. 8:104.

Christophers, S. R.

*i90i. The Anatomy and Histology of the Adult Female Mosquito. Reports
to the Malarial Committee of the Roy. Soc. (4) , 20 pp. ; 6 pi. London
(Harrison and Sons).
CoMSTOCH, J. H., and Kochi, C.

1902. The Skeleton of the Heads of Insects. Am. Nat., 36:13-45; 29 fig.
Cragg, F. W.

*I9I2. Studies on the Mouth-parts and Sucking Apparatus in the Blood-
sucking Diptera. No. i. Philaematomyia insignis Austen. Sci. Mem. Med.
Ind., No. 54; 15 pp.; 5 pi. Calcutta.

DiMMOCK, G.

1881. The Anatomy of the Mouth-parts and of the Sucking Apparatus of
some Diptera. Dissertation. 50 pp.; 4 pi. Boston.

1882. Anatomy of the Mouth-parts and of the Suctorial Apparatus of Culex.
Psyche, 3:231-241.

Frey, R.

1913. tJber die Mundteile der Mycetophiliden, Sciariden, und Cecidomyiiden.
Acta Soc. Fauna Flora Fenn., 37, No. 2. 54 pp. ; 4 pi., i fig.
Gerstfeldt, G.

*i853. tJber die Mundteile der saugenden Insekten. Dissertation. 121 pp. ;
4 pi. Dorpat.
Giles, G. M.

♦1905. Mouth-parts of the Biting Flies. — Preliminary Note. Jour. Trop.
Med., 8:363-364. London.

*An asterisk indicates publications that have not been seen by the author.

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1906. Mouth-parts of the Biting Flies of the Genera Stomoxys and Glossina.
Jour. Trop. Med., 9:99-102, 153-156, 169-173, 182-186, 198-202, 217-219, 235-
236. London.
Grunberg, K.

1906. tJber blutsaugende Musciden. Zool. Anz., 30:78-93; 15 fig.

1907. Die blutsaugenden Dipteren. Leitfaden. Jena (Fischer).
Hammond, A.

1874. The Mouth of the Crane-fly. Sci. -Gossip, 1874:155-160; fig. 97-113.
Hansen, H. J.

1883. Fabrica oris dipterorum : Dipterernes Mund i anatomisk og sys-
tematisk Henseende. Kjobenhavn. pp. 1-220; pi. 5.
Harris, W. H.

1902. The Dentition of the Diptera. JoMr. Quek. Micr. Club (.2), 8:389-
398; pi. 19, 6 fig.
Hewitt, C. G.

1907. The Structure, Development and Bionomics of the House-fly, Musca
domestica, Linn. Part L — Anatomy of the Fly. Quart. Jour. Micr. Sci.,
51:395-448; pi. 22-26.
Hunt, G.

1856. The Proboscis of the Blow-fly. Quart. Jour. Micr. Sci.. 4:238-239;
2 fig.
Kellogg, V. L.

1899. The Mouth Parts of the Nematocerous Diptera. Psyche, 8:303-306,

327-32,0, 346-348, 355-359, 363-365; n fig.
1902. The Development and Homologies of the Mouth Parts of Insects.
Am. Nat, 36:683-706; 26 fig.
Kolbe, H. J.

1893. Insektenkunde. 8°, 724 pp. Berlin.
Kbaepelin, K.

1882. liber die Mundwerkzeuge der saugenden Insecten. Vorlaufige Mitthei-
lung. Zool. Anz., 5 :574-579 ; 3 fig-

1883. Zur Anatomic und Physiologic des Riissels von Musca. Zeitschr. wiss.
Zool., 39:683-719; pi. 40-41.

Kulagin, N.

1905. Der Kopfbau bei Culex und Anopheles. Zeitschr. wiss. Zool., 83 :285-

335 ; 3 pl-
Langhoffer, a. ,

1888. Beitrag zur Kenntnis der Mundteile der Dipteren. Dissertation. 32

pp. Jena.
1901. Mandibulae Dolichopodidarum. Verhandl. Internat. Zoologen-Con-
gress, Berlin, 5:840-846; 4 fig.
Leon, N.

1904. Vorlaufige Mitteilung iiber den Saugrussel der Anopheliden. Zool.
Anz., 27:730-732; I fig.
Lowne, B. T.

1870. The Anatomy and Physiology of the Blow-fly (Musca vomitoria,
Linn.). 121 pp.; 10 pl.

229] HEAD OF DIPTERA — PETERSON ' 59

1893. A Reply to some Observations on the Mouth-organs of the Diptera.

Ann. Mag. Nat. Hist. (6), 11:182-184.
1890-95. The Anatomy, Physiology, Morphology and Development of the

Blow-fly (Calliphora crythrocephala). 778 pp.; 52 pi. London (R. H.

Porter).
MacCloskie, G.

1880. The Proboscis of the House-fly. Am. Nat, 14:153-161; 3 fig.
1884. Kracpelin's Proboscis of Musca. Am. Nat, 18:1234-1244; 12 fig.
1888. The Poison-Apparatus of the Mosquito. Am. Nat., 22:884-888; 2 fig.

Marlatt, C. L.

1896. The Mouth-parts of Insects, with particular Reference to the Diptera
and Hemiptera. Abstract, Proc. A. A. A. S., 44:154-155.
Meinert, F.

1880. Sur la Conformation de la Tete et sur ITnterpretation des Organes
buccaux chez les Insectes ainsi que sur la Systematique de cet Ordre.
Entom. Tidskrift, i :i47-i5o.

1880a. Sur la Constitution des Organes buccaux chez les Dipteres. Entom.
Tidskrift., i :I50-I53.

1881. Fluernes Munddele Trophi Dipterorum. 91 pp.; 6 pi. Kjobenhavn.

1882. Die Mundtheile der Dipteren. Zool. Anz., 5 :570-574, 599-603.
Menzbier_, M. a.

*i88o. tJber der Kopfskelett und die Mundteile der Zweifliigler. Bull. Soc.
Imp. Nat Moscou, 55 :8-7i ; 2 pi.

MtJGGENBURG, F. H.

1892. Der Riissel der Diptera pupipara. Arch. Naturg., 58 :287-332 ; 2 pi.
Packard, A. S.

1903. A Textbook of Entomology. 8°, 715 pp. New York.
Patton, W. S., and Cragg, F. W.

1913. A Textbook of Medical Entomology. London, Madras, and Calcutta
(Christian Literature Society for India).
Pazos y Caballera, F. H.

1903. Del exterior e interior del Mosquito. Apuntes sobre la Anatomie y
Morfologia. Rev. Trop. Med., 4 :209-2i8 ; 4 pi.
Peterson, Alvah

1915. Morphological Studies on the Head and Mouth-parts of the Thy-
sanoptera. Ann. Ent. Soc. Amer., 8:20-67; 7 pl-
Smith, J. B.

1890. A Contribution to a Knowledge of the Mouth Parts of the Diptera.
Trans. Am. Ent Soc, 17:319-339; 22 fig.
Stephens, J. W. W., and Newstead, R.

♦1907. The Anatomy of the Proboscis of Biting Flies. Ann. Trop. Med.,
1:171-198; 8 pl. Liverpool.
Steinheil, a. p.

1896. Trophi of Tabanus. Studies from the Lab. Zool., Dipt, Imp. Univ.
Warsaw, 1896:247-250; 2 fig.

60 ILLINOIS BIOLOGICAL MONOGRAPHS [230

Suffolk, W. T.

1869. On the Proboscis of the Blow-fly. Monthly Micr. Jour., 1:331-342;

4 pl-
Wateehouse, C. O.

♦1893. Some Observations on the Mouth-organs of Diptera. Ann. Mag. Nat
Hist. (6), 11:45-46.
Wesch6, W,

1902. Undescribed Palpi on the Proboscis of some Dipterous Flies, with
Remarks on the Mouth-parts in several Families. Jour. Roy. Micr. Soc,
1902:412-416; 2 pl.
♦1903. The Mouth-parts of the Tsetse-fly. Knowledge, 26:116-117; i fig.
1904. The Labial and Maxillary Palpi in Diptera. Trans. Linn. Soc. Lon-
don, 9:219-230.
1906. The Genitalia of both Sexes in Diptera and their Relation to the
Armature of the Mouth. Trans. Linn. Soc. London, 9:339-386; 8 pl.

1908. The Proboscis of the Blow-fly, Calliphora erythrocephala. A Study
in Evolution. Jour. Quek, Micr. Club (2), 10:283-295; 2 pl.

1909. The Mouth-parts of the Nemocera and their Relations to the other
Families in Diptera. Corrections and Additions to the Paper published in
1904. Jour. Roy. Micr. Soc, 1909:1-16; pl. 1-4.

1912. The Phylogeny of the Nemocera, with Notes on the Leg Bristles,
Hairs and certain Mouth Glands of Diptera. Biol. Bull., 23:250-270; i pl.

231]

HEAD OF DIPTERA— PETERSON

EXPLANATION OF PLATES

ABBREVIATIONS USED

a.a

Anterior arms of the tentorium

i.a.d

Invagination of the anterior and

a.e.s

Arms of the epicranial suture

dorsal arms of the tentorium

a.f

Antennal fossa

i.d

Invagination of the dorsal arm

al.c

Alimentary canal

of the tentorium

ant

Antenna

i.p

Invagination of the posterior

Arista

arm of the tentorium

a.s

Antennal sclerite

Kappa (sclerite)

bph

Basipharynx

Labrum

bpr

Basiproboscis

Lacinia

b.t

Body of the tentorium

Labella

Clypeus

l.ep

Labrum epipharynx

Cardo

Ligula

c.e

Compound eye

Labium

Chitinized

Membrane

ch.th

Chitinized thickening

Mandible

c.l.s

Clypeo-labral suture

Mentum

Cornu

mpr

Mediproboscis

d.a

Dorsal arms of the tentorium

m.ps

Main pseudotracheae

Depression

Maxilla

dpr

Distiproboscis

mx.pl

Maxillary palpus

Epipharynx

n.s

Neck sclerite

e.s

Epicranial suture

Ocellus

Furca, also f-i, f-2, and f-3

oca

Ocellar area

Facet

occ

Occiput

Flagellum

Oesophagus

Front

oe.p

Oesophageal pump

fr.c

Fronto-clypeus

o.f

Occipital foramen

fr.s

Frontal suture

0.1

Oral lobe

Galea

o.s

Ocular sclerite

Gena

p.a

Posterior arms of the tentorium

Glossa

Pedicel

Hook

Pgl

Paraglossa

Hypopharynx

Postgena

Hyoid

pocc

Parocciput

i.a

Invagination of the anterior arm

ppo

Parapostgena

of the tentorium

Proboscis

ILLINOIS BIOLOGICAL MONOGRAPHS

[232

ps Pseudotrachea

ps.th Pseudotracheal thickening

pt Ptilinum

r.d.a Rudimentary dorsal arms of the

tentorium

r.p.a Rudimentary posterior arms of

the tentorium

s Suture

s.b Salivary bulb

sc Scape

s.d Salivary duct

s.e.s Stem of the epicranial suture

si Sigma (sclerite)

so Sense organ

s.s Secondary suture

st Stipes, st-i and st-2 ectal part,

st-e ental part

su Submentum

su.me Submentum and mentum

t Tentorium

tee Teeth-like structures

th Thickening

the Theca

to Torma or tormae

t.th Tentorial thickening

V Vertex

2^^] HEAD OF DIPTERA—PETERSON 63

PLATE I

64 ILLINOIS BIOLOGICAL MONOGRAPHS [234

EXPLANATION OF PLATE
Cephalic Aspect of the Head and Mouth-parts

Hypothetical head.
Siinuliuin vcnnstiiin , female.
Siuniliuni johannseni, male.
Bibiocephala clcgaiitiila, male.
Bibiocephala elegantula, female.
Rhabdophaga strobiloides.
Mycctobia divcrgcns.
Psychoda albipennis.
Rhyphns punctatns.
Psorophora ciliata, female.
Mycetophila punctata, female.
Chiro)ioi)!us ferrugincovittatus, female.
Bibio fcinoratus, male.
Bibio femoratus, female.
Ptychoptcra rufocincta.
Trichocera bimacula.
Sciara varians.
Tiptila bicornis.

Fig.

10.

Fig.

II.

Fig.

12.

Fig.

13-

Fig.

14-

Fig.

15-

Fig.

i6.

Fig.

17-

Fig.

i8.

ILLIXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE I

235] HEAD OF DIPTERA— PETERSON 65

PLATE II

ILLINOIS BIOLOGICAL MONOGRAPHS

[236

EXPLANATION OF PLATE

Cephalic aspect of the Head

Fig.

19.

Fig.

20.

Fig.

22.

Fig.

23-

Fig.

24.

Fig.

25-

Fig.

27-

Fig.

29.

Fig.

31-

Fig.

37-

Fig.

Di.ra clavata.

Tabanns giganteus, female.

Tab anus giganteus, male.

Promachiis vcrtehratus.

Eristalis tcnax, female.

Eristalis tcnax, dorsal end of the tormae.

Eristalis tenax, male.

Psorophora ciliata, male.

Strationiyia apicula, male.

Stratio)nyia apicula, female.

Exoprosopa fasciata.

Mydas clavattis.

Aphiochaeta agarici.

Platypeca velutina.

Psiloccphala hacinorrlwidalis, male.

Leptis vertebrata, female.

Lcptis vertebrata, male.

Psiloccphala haeniorrhoidalis, female.

Lonchoptera lutea, female.

Pipunculus ciiigulatus, female.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Pipunculus 9

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE H

237] HEAD OF DIPTERA — PETERSON 67

PLATE III

ILLINOIS BIOLOGICAL MONOGRAPHS [238

Fig.

39-

Fig.

40.

Fig.

41.

Fig.

42.

Fig.

43.

Fig.

44-

Fig.

45-

Fig.

46.

Fig.

47-

Fig.

48.

Fig.

49.

Fig.

50.

Fig.

51-

Fig.

52.

Fig.

53-

Fig.

54-

Fig.

55-

Fig.

56.

Fig.

57-

EXPLANATION OF PLATE
Cephalic Aspect of the Head

Pipun cuius cingulatus, male.
Eiiipis clausa, female.
Sccnopinus fenestralis, male.
Scenopinus fenestralis, female.
Dolichopus bifractus.
Calobata univitta.
Drosophila ampelophila.
Sepsis violacea.
Desiitometopa latipes.
Oecothea fenestralis.
Hctcroneura flaviseta.
Chyromya concolor.
Chloropisca glabra.
Sphyracephala brevicornis.
One odes costatus.
Gastrophilus eqiii.
Tetanocera plumosa.
Ochthera mantis.
Olfersia ardeae.

ILLINOIS BIOLOGICAL MOXOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE III

239] HEAD OF DIPTERA — PETERSON 69

PLATE IV

ILLINOIS BIOLOGICAL MONOGRAPHS

[240

Fig

58.

Fig

59-

Fig

60.

Fig

61.

Fig

62.

Fig

63.

Fig

64.

Fig

65.

Fig

66.

Fig

67.

Fig

68.

Fig

69.

Fig

71-

Fig

72.

EXPLANATION OF PLATE

Cephalic Aspect of the Head

Coelopa vanduseii.
Loxocera pectoralis.
Sapromyza vulgaris.
Euaresta acqualis.
Scatophaga furcata.
Borborus cquiniis.
Chrysoiityca deiiiandata.
Thelaira leucozona.
Sarcophaga haemorrhoidalis.
Conops hrachyrhynchus.
Archytas analis.
Hydro taea dentipcs, female.
Hydrotaea dentipes, male.
Musca domestica, female.
Musca domestica, male.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE IV

241] HEAD OF DIPTERA— PETERSON 71

PLATE V

72 ILLINOIS BIOLOGICAL MONOGRAPHS [242

EXPLANATION OF PLATE
Caudal Aspect of the Head

Fig. y^)- Hypothetical head.

Fig. 74. Tahanus giganteus, female.

Fig. 75. Tabanus giganteus, male.

Fig. 76. Bibiocephala elegantula, male.

Fig. 77. SimuUum veiiustuin, female.

Fig. 78. Trichocera biinacula.

Fig. 79. Dixa clavata.

Fig. 80. Rhyphus punctatus.

Fig. 81. Sciara varians.

Fig. 82. Psychoda albipennis.

Fig. 83. Bibiocephala elegantula, female.

Fig. 84. Promachus vcrtebratus.

Fig. 85. Bittaconwrpha elavipes.

Fig. 86. Rhabdopliaga strobiloides.

Fig. 87. Mycetophila punctata.

Fig. 88. Chironomus ferrugineovittatus.

Fig. 89. Chironomus ferrugineovittatus, dorsal aspect.

Fig. 90. Mycetobia divergens.

ILLIXOIS BIOLOGICAL MOXOGRAPHS

VOLUME 3

PETERSON HEAD AXD MOUTH PARTS OE DIPTERA PLATE V

243] HEAD OF DIPTERA— PETERSON 72,

PLATE VI

ILLINOIS BIOLOGICAL MONOGRAPHS

[244

EXPLANATION OF PLATE
Caudal Aspect of the Head

Fig. 91. Bibio femoratus, male.

Fig. 92. Bihio femoratus, female.

Fig. 93. Liiiinobia immatura.

Fig. 94. Sphyracephala brevicornis.

Fig. 95. Tipula bicornis.

Fig. 96. Psorophora cilia ta, female.

Fig. 97. Eiiipis clausa, female.

Fig. 98. Exoprosopa fasciata.

Fig. 99. Mydas clavatus.

Fig. 100. Psilocephala haeniorrhoidalis, female.

Fig. loi. Ochthera mantis.

Fig. 102. Lonchoptera lutea, female.

Fig. 103. Leptis vertebrata, male.

Fig. 104. Stratiomyia apicula, male.

Fig. 105. Oncodes costatus.

Fig. 106. Piptmculus cingulatiis, female.

Fig. 107. Sccnopinns fcncstralis.

Fig. 108. Dolichopus sp.

Fig. 109. Oncodes costatus, ventral aspect.

Fig. no. Platypeza velutina.

Fig. III. Aphiochaeta agarici.

Fig. 112. Dolichopus bifractiis, lateral margins incomplete.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

109 Onccxies

PETERSON HEAD AXD MOUTH PARTS OE DIPTERA PLATE VI

245] HEAD OF DIPTERA — PETERSON 75

PLATE VII

ILLINOIS BIOLOGICAL MONOGRAPHS

[246

EXPLANATION OF PLATE
Caudal Aspect of the Head

Fig.

[13

Eristalis tciiax, female.

Fig.

Calobata imivitta.

Fig. ]

Saproiiiyca vulgaris.

Fig.

[i6

Lispa nasoni, margin incomplete.

Fig.

Conops brachyrhynchus.

Fig.

Sepsis violacea.

Fig.

Tctanoccra pluiiiosa.

Fig. J

Myiospila incditabunda, margin incomplete

Fig.

Coelopa vanduzcii.

Fig.

Chiromya concolor.

Fig. ]

Loxocera pectoralis.

Fig. ]

Archytas analis.

Fig. ]

Drosophila ampclophila.

Fig. 1

Heteroneura flaviseta.

Fig. ]

Hydrotaea dentipes.

Fig. ]

Thelaira leucocona.

Fig. ]

Dcsmoutetopa latipes.

Fig. ]

Sarcophaga Jiaem orrhoidalis.

Fig. ]

Eiiaresta acqnalis.

Fig. ]

Chloropisca glabra.

Fig. ]

2,2

Musca doiiicstica, female.

Fig. ]

Chrysoiiiyca detnaiidata.

Fig. ]

Scatophaga furcata.

Fig. ]

Borborus cqninus.

ILLIXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AXD MOUTH PARTS OF DIPTERA PLATE VH

247] HEAD OF DIPTERA — PETERSON 77

PLATE VIII

ILLINOIS BIOLOGICAL MONOGRAPHS

[248

EXPLANATION OF PLATE
Caudal and Lateral Aspects of the Head and the Tentorium

Oecothea fenestralis, caudal aspect.

Gastrophilus equi, caudal aspect.

Olfersia ardeae, caudal aspect.

Hypothetical head, lateral aspect.

Hypothetical tentorium, lateral aspect.

Tabanus giganteus, female, lateral aspect.

Tabaiius giganteus, lateral aspect of the tentorium.

Siinulium venustum, female, lateral aspect.

Leptis vertebrata, male, lateral aspect.

Mydas clavatus, lateral aspect.

Proviachus vertebratus, lateral aspect.

Promachus vertebratus, lateral aspect of the tentorium.

Scenopiuus fenestralis, female, lateral aspect.

Sciara various, lateral aspect.

Piptmcuhis eiiigulatus, lateral aspect.

Chironomus ferrugineovittatus, lateral aspect.

Bibio fciuoratus, female, lateral aspect.

Bibio feiiwratiis, male, lateral aspect.

Fig.

^37

Fig.

t38

Fig. :

139

Fig.

[40.

Fig.

[41

Fig. ]

42.

Fig.

f43

Fig. ]

44.

Fig.

45-

Fig. ]

46.

Fig. 1

47-

Fig. ]

48.

Fig. ]

49-

Fig. ]

50.

Fig. ]

51.

Fig. ]

52.

Fig. ]

53-

Fig. ]

54-

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Pipunculus

161

PETERSON HEAD AXD MOUTH PARTS OF DIPTERA PLATE VHI

249] HEAD OF DIPTERA — PETERSON

PLATE IX

ILLIXOIS BIOLOGICAL MONOGRAPHS

[2sa

EXPLANATION OF PLATE

Lateral Aspect of the Head showing the Tentorium

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
■^ig.
-""ig-
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

55. Bibioccphala clcgantiila, female.

56. Bibioccphala degantula, male.

57. Rhyphus punctatus.

58. Trichoccra biuiacula.

59. PsoropJiora ciliata, female.

60. Stratiomyia apicitia, male.

61. Mycetobia diver gens.

62. Exoprosopa fascia ta, eye removed.

63. Dixa clavata.

64. Em pis claiisa, female.

65. Plaiypcza vclutina.

66. Psychoda albipcniiis.

67. Eristalis tcua.r, female, eye removed.

68. Dolichopus bifractus. eye removed.

69. Loxoccra pcctoralis.

70. Rhabdophaga strobiloides.

71. Sapromyca vulgaris.

72. Drosophila ampclnphila.

72)- Psilocephala haeiuorrhoidalis, female.

74. Aphiochaeta agarici.

75. Euaresta aequalis.

76. Heteroneura ftaviseta.

77. Lonchoptera lutea.

78. Tipula bicornis.

79. Chyroiiiya concolor.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE IX

251] HEAD OF DIPTERA— PETERSON

PLATE X

ILLINOIS BIOLOGICAL MONOGRAPHS

[252

EXPLANATION OF PLATE
Lateral Aspect of the Head showing the Tentorium

Fig. i8o. Tetanocera plumosa.

Fig. i8i. Chrysoniyza deuiandata.

Fig. 182. Coelopa vanduseii.

Fig. 183. Calobata univitta.

Fig. 184. Sepsis violacea.

Fig. 185. Desiiwinetopa latipcs.

Fig. 186. Conops brachyrhynchus.

Fig. 187. Ochthera mantis.

Fig. 188. Borborus cquiiius.

Fig. 189. Chloropisca glabra.

Fig. iggh. Hypothetical antenna.

Fig. 199. Dixa clavata.

Fig. 200. Trichocera bimacula.

Fig. 201. Rhabdophaga strobiloides.

Fig. 202. Psychoda albipennis.

Fig. 203. Bibiocephala elegantula.

Fig. 204. Siinuliuni venustuin.

Fig. 205. Sciara z'arians.

Fig.

190.

Fig.

191.

Fig.

192.

Fig.

193-

Fig.

194.

Fig.

195-

Fig.

196.

Fig.

197.

Fig.

198.

Antennae

Fig.

206.

Fig.

207.

Fig.

208.

Fig.

209.

Fig.

210.

Fig.

211.

Sphyracephala brevicornis.
Sarcophaga haeiuorrhoidalis.
Oecothea fcnestralis.
Scatophaga furcata.
Musca domestica.
Hydrotaea dentipes.
Thelaira leucocona.
Archytas analis.
Olfersia ardeae.

Chiroiw lints ferrugineovitta-

tiis, female.
Cliiroiioinus ferriigineovitta-

tns, male.
Bibio femoratus, female.
Rhyphus punctatus.
Psorophora ciliata, female.
Psorophora ciliata, male.

ILLIXOIS BIOLOGICAL MOXOGRAPHS

I'OLUME 3

PETERSOX HEAD AXD MOUTH PARTS OF DIPTERA PLATE X

253] HEAD OF DIPTERA — PETERSON

PLATE XI

ILLINOIS BIOLOGICAL MONOGRAPHS

[254

EXPLANATION OF PLATE

Fig. 212.

Fig. 213.
Fig. 214.
Fig. 215.
Fig. 216.
Pig. 217.
Fig. 218.
Fig. 219.
Fig. 220.
Fig. 221.
Fig. 222.
Fig. 223.
Fig. 224.
Fig. 225.
Fig. 226.
Fig. 227.
Fig. 228.
Fig. 229.
Fig. 230.

Fig. 250.
Fig. 251.
Fig. 252.
Fig. 253.

Antennae

Mydas clavatus.

Fig.

231

Stratiomyia apicula.

Fig.

232.

Tabanus giganteus.

Fig.

233-

Ejiipis clausa.

Fig.

234-

Exoprosopa fasciata.

Fig.

235-

Promachus vertebratus.

Fig.

236.

Leptis vertebrata.

Fig.

237-

Scenopinus fenestralis.

Fig.

238

Oncodes costatus.

Fig.

239

Conops brachyrhynchus.

Fig.

240

Platypeca veliitina.

Fig.

241

Lonchoptera lutea.

Fig.

242

Aphiochaeta agarici.

Fig.

243

Tctanocera plumosa.

Fig.

244

Dolichopus bifractus.

Fig.

245

Oecothea fenestralis.

Fig.

246

Desrnonietopa latipes.

Fig.

247

Heteroneura flaviseta.

Fig.

248

Thelaira Icucozona.

Fig.

249

Mandibles

Siitiuliuiii venustuiii, fern

ale.

Fig.

254

Psorophora ciliata, female.

Fig.

255

Siinulium johannseni, ma

le.

Fig.

256

Cidicoides sangiiisugus.

female.

Borborus equinus.
Eristalis tenax.
Chyromya concolor.
Sepsis violacea.
Loxocera pectoralis.
Calobata univitta.
Ochthera mantis.
Drosophila ampelophila.
Gastrophilus equi.
Euaresta aequalis.
Hydrotaea dentipes.
Musca domestica.
Pipunculus cingiUatus.
Sarcophaga hacinorrhoidalis.
Chrysomysa demandata.
Scatophaga furcata.
Archytas analis.
Sapromysa vulgaris.
Olfersia ardeae.

Dixa iiiodesta, female.
Tabanus giganteus, female.
Bibiocephala elegantula,
female.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XI

255] HEAD OF DIPTERA — PETERSOX 85

PLATE XII

86 ILLINOIS BIOLOGICAL MONOGRAPHS [256.

EXPLANATION OF PLATE

Mandible and Maxillae

Fig. 256h. Hypothetical mandible.

Fig. 257. Hypothetical maxillae.

Fig. 258. Siiiiuliuiii venustuin, female, cephalic aspect.

Fig. 259. Tahaniis giganteus, female, caudal aspect.

Fig. 260. Trichocera biinacula, caudal aspect.

Fig. 261. Rhyphus ptinciatus, caudal aspect.

Fig. 262. Dixa clavata, caudal aspect.

Fig. 263. Psychoda albipennis, caudal aspect.

Fig. 264. Bihio feinoratus, caudal aspect.

Fig. 265. CtiUcoides sanguisugns, female, caudal aspect.

Fig. 266. Psorophora ciliata, female and male, caudal aspect.

Fig. 267. Sciara varians, caudal aspect.

Fig. 268. Rhabdophaga strohiloides, caudal aspect.

Fig. 269. Bibiocephala elegantula, female, caudal aspect.

Fig. 270. Chironoiuus ferrngineovittatus, cephalic aspect.

Fig. 271. My das clavatus, lateral aspect.

Fig. 272. Platypcza velutina, lateral aspect.

Fig. 273. Stratiomyia apicula, cephalic aspect.

Fig. 274. Empis clausa, lateral aspect.

Fig. 275. Leptis vertebrata, caudal aspect.

Fig. 276. Promachus vertebratus, caudal aspect.

Fig. 277. Tipula bicortiis, portion of caudal aspect.

Fig. 278. Aphiochacta agarici, lateral aspect.

Fig. 279. Pipimculns cingulatus, lateral aspect.

Fig. 280. Loiichoptera lutea.

Fig. 281. Psiloccphala hacmorrhoidalis, cephalic aspect.

Fig. 282. Scenopinus fenestralis.

Fig. 283. Tabanus giganteus, male, caudal aspect.

Fig. 284. Dolichopus bifractus.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

279 P,pun<4ll,

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XH

257] HEAD OF DIPTERA — PETERSON 87

PLATE XIII

88 ILLINOIS BIOLOGICAL MONOGRAPHS [258

EXPLANATION OF PLATE
Maxillae

Fig. 284a. Eulonchus tristis.

Fig. 285. Exoprosopa fasciata.

Fig. 286. Eristalis tenax.

Fig. 287. Sepsis viola cea.

Fig. 288. Coelopa vanduzeii.

Fig. 289. Sapromysa vulgaris.

Fig. 290. Oecothca fenestralis.

Fig. 291. Drosophila aiiipclophila.

Fig. 292. Euarcsta acquaUs.

Fig. 293. Spliyraccphala brevicornis.

Fig. 294. Borborus cquiiius.

Fig. 295. Chrysoiiiyca dcmandata.

Fig. 296. Calobata univitta.

Fig. 297. Ochthera mantis.

Fig. 298. Heteroneura flaviseta.

Fig. 299. Chyroiuya concolor.

Fig. 300. Loxocera pectoralis.

Fig. 301. Tlielaira leuco::oHa.

Fig. 302. Tctanoccra phimosa.

Fig. 303. Desnioynetopa latipes.

Fig. 304. Musca domestica.

Fig. 305. Conops brachyrhynchus.

Fig. 306. Chloropisca glabra.

Fig. 307. Scatophaga furcata.

Fig. 308. Hydrotaca dcntipes.

Fig. 309. Archytas analis.

Fig. 310. Sarcophaga haeiiwrrhoidalis.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

v:^;:'> <;Ag^. st-e ■':■;: f:*;

PETERSON HEAD AXD MOUTH PARTS OF DIPTERA PLATE XIII

259] HEAD OF DIPTER A— PETERSON 89

PLATE XIV

ILLINOIS BIOLOGICAL MONOGRAPHS

[260

EXPLANATION OF PLATE
Lateral Aspect of the Mouth-parts or Proboscts

Trichocera biniacula.
Chironoiiius ferrugineovittatus.
Rhabdophaga strobiloides.
Sciara varians.
Bibio feiiioratus.
Simulium venustum, female.
Tabanus giganteus, female.
Psychoda albipennis.
Mydas clavatus.
Lonchoptera lutea.
Rhyphus punctatus.
Proniachus vertebratus.
Leptis vertebrata.
Psilocephala haenwrrhoidalis.
Scenopinus fenestralis.
Platypesa velutina.
Pipunculus cingulatus.
Eristalis tenax.
Sapromyza vulgaris.
Desmonietopa latipes.
Stratiomyia apicula.
Oecothea fenestralis.
Chyromya concolor.

Fig.

311-

Fig.

312.

Fig.

313-

Fig.

314-

Fig.

315-

Fig.

316

Fig.

317.

Fig.

318

Fig.

319-

Fig.

320.

Fig.

321.

Fig.

322.

Fig.

323

Fig.

324.

Fig.

325.

Fig.

326

Fig.

327

Fig.

328

Fig.

329.

Fig.

330

Fig.

331

Fig.

332

Fig.

333

ILLIXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

327 P.punculu, 328 Eristalis 329 S.protny;

331 Siraliomyja 333Chyromy.

PETERSON HEAD AXD MOUTH PARTS OF DIPTERA PLATE XIV

.261] HEAD OF DIPTERA— PETERSON 91

PLATE XV

ILLINOIS BIOLOGICAL MONOGRAPHS

[262

EXPLANATION OF PLATE
Lateral Aspect of the Proboscis

Fig. 334
Fig. 335
Fig. 336
Fig. 337
Fig. 338
Fig. 339
Fig. 340
Fig. 341
Fig. 342
Fig. 343
Fig. 344
Fig. 345
Fig. 346
Fig. 347
Fig. 348
Fig. 349

Sepsis violacea.
Aphiochacta agarici.
Ochthera mantis.
Coelopa vanduseii.
Sphyracephala brevicornis.
Loxocera pectoralis.
H eteroneura flaviseta.
Chrysoiiiyca dcinandata.
Borborus equinus.
Drosophila anipclophila.
Tetanocera plumosa.
Chloropisca glabra.
Thelaira leucozona.
Euarcsta aequalis.
Calobata univitta.
Hydrotaea dentipes.

ILLINOIS BIOLOGICAL MOXOGRAPHS

VOLUME 3

347 Euaresia 348 CalobaU

PETERSON HEAD AXD xMOUTH PARTS OF DIPTERA PLATE XV

263] HEAD OF DIPTER A— PETERSON 93

PLATE XVI

ILLINOIS BIOLOGICAL MOXOGRAPHS

[264

Fig. 350
Fig. 351
Fig. 352
Fig. 353
Fig. 354
Fig. 355
Fig. 356
Fig. 357
Fig. 358
Fig. 359
Fig. 360
Fig. 361
Fig. 362
Fig. 363
Fig. 364
Fig. 364a
Fig. 365
Fig. 366.
Fig. 367
Fig. 368
Fig. 369
Fig. 370

EXPLANATION OF PLATE
Mouth-parts

Sarcopliaga haetiwrrhoidalis, lateral aspect.

Miisca doinestica, lateral aspect.

Euipis clausa, lateral aspect.

Archytas analis, lateral aspect.

Stoiiioxys calcitrans, lateral aspect.

Siphona gcnicidata, lateral aspect.

Coiiops hrachyrliynchiis, lateral aspect.

Scatophaga furcata, lateral aspect.

Olfersia ardeae, lateral aspect.

Stylogaster biannulata, caudal aspect.

Sciara varians, maxillae and labium, cephalic aspect.

Exoprosopa fasciata, lateral aspect.

Hypothetical and typical labium, mesal aspect.

Hypothetical mouth-parts, lateral aspect.

Bibio feinoratus, maxillae and labium, cephalic aspect.

Eulonchus tristis, head and mouth-parts, lateral aspect.

Trichocera bimacula, maxillae and labium, cephalic aspect.

Sinmlium venustum, maxillae and labium, cephalic aspect.

Rhabdophaga strobiloidcs, maxillae and labium, caudal aspect

Leia oblcctabilis, maxillae and labium, cephalic aspect.

Leptis vertebrata, mesal aspect of glossa.

Leptis vertebrata, maxillae and labium, caudal aspect.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XVI

265] HEAD OF DIPTERA— PETERSON 95

PLATE XVII

ILLIXOIS BIOLOGICAL MOXOGRAPHS

[266

EXPLANATION OF PLATE

i'ig

371.

Fig

372

Fig

373-

Fig

374

Fig

375-

Fig

3/6

Fig

377-

Fig

378

Fig

379-

Fig

380.

Fig

381.

Fig

382

Fig

383.

Fig

384

Fig

385.

Fig

386.

Fig

387.

Fig

388.

Fig

389.

Fig

390.

Fig

391

Fig

392.

Fig

393

Fig

394-

Maxillae and Labium

CliironoJiius fcrrugincoiittatus, cephalic aspect.
Psychodit albipcnnis, cephalic aspect.

Psoroplwra cilicita, female, portions of mandibles, maxillae, labium, ten-
torium, and head-capsule.
Rhyphus punctatiis, cephalic aspect.
Dixa clavata, cephalic aspect.
Promachus vcrtcbratus, caudal aspect.
Prouiachtis vertebratus, labium, cephalic aspect.
Promachus vertebratus, cross-section of labium, see figure 377.
Promachus vertebratus. distal end of labium, cephalic aspect.
Psorophora ciliata. distal end of labium, caudal aspect.
Psorophora ciliata, distal end of labium, cephalic aspect.
Geranomyia canadensis, cephalic aspect.
Tipula bicornis, distal end of labium, mesal aspect.
Tipiila bicornis, caudal aspect of labium.
Hclobia punctipcnnis, caudal aspect.
Liiimobia iinmattira, caudal aspect.
Dixa clavata, caudal aspect of labium.

Tipula bicornis, sclerites about distal end of theca of labium.
Bittacomorpha clavipcs, distal end of labium, mesal aspect.
Tabanus giganteus, mesal aspect of labium.
Tabanus giganteus, caudal aspect of labium.
Tabanus giganteus, cephalic aspect of labium.
Aphiochaeta agarici, caudal aspect.
Aphiochaeta agarici, distal end of labium, mesal aspect.

ILLIXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XVII

^67] HEAD OF DIPTERA — PETERSOX 97

PLATE XVIII

ILLIXOIS BIOLOGICAL MONOGRAPHS

[268:

EXPLANATION OF PLATE

Fig.

395-

Fig.

396.

Fig.

397-

Fig.

398.

Fig.

399.

Fig.

400.

Fig.

401.

Fig.

402.

Fig.

403.

Fig.

404.

Fig.

405-

Fig.

406.

Fig.

407.

Fig.

408.

Fig.

409.

Fig.

410.

Fig.

411.

Fig.

4I'2.

Fig.

413.

Fig.

414.

Fig.

415-

Fig.

416.

Fig.

417.

Fig.

418.

Fig.

419-

Fig.

420.

Fig.

421.

Fig.

422.

Fig.

423.

Fig.

424.

Fig.

425-

Fig.

42Sa

Fig.

425b

Fig.

426.

Fig.

427.

Fig.

42S.

Fig.

429.

Labium

Stratioiuyia apicula, caudal aspect of proboscis.

Stratiomyia apicula, mesal aspect.

Mydas clavatus, caudal aspect.

Mydas clavaius, cephalic aspect.

Bibiocephala elcgantiila, cephalic aspect.

Sccnopinus fenestralis, mesal aspect.

Scenopinus fenestralis, caudal aspect.

Psilocephala hacniorrhoidalis, caudal aspect.

Psiloccphala haeiiiorrhoidalis, mesal aspect.

Desiiioiiietopa latipes, caudal aspect.

Dcsnwtiietopa latipes, cephalic aspect.

Lonchoptera liitca, caudal aspect.

Louchoptera liitca, cephalic aspect.

Lonchoptera liitca, mesal aspect.

Saproniyca vulgaris, caudal aspect.

Saproiny::a vulgaris, mesal aspect.

Chyroniya concolor, caudal aspect.

CJiyroniya concolor, mesal aspect.

Euaresta aequalis, caudal aspect.

Euaresta aequalis, mesal aspect.

Platypeza velutina, mesal aspect.

Platypcza velutina, caudal aspect.

Conops brachyrhynclius. distal end, caudal aspect.

Conops brachyrhynchus, distal end, lateral aspect.

Conops brachyrhynchus, distal end. cephalic aspect.

Conops brachyrhynchus, caudal aspect.

Enipis clausa, caudal aspect.

Einpis clausa, portion of cephalic aspect.

Eiiipis clausa, cephalic aspect.

Rhaniphoniyia glabra, caudal aspect.

Rhainphoinyia glabra, mesal aspect.

Eulonchus tristis, cephalic aspect.

Eulonchus tristis, distal end, mesal aspect.

Exoprosopa fasciata, distal end, caudal aspect.

Exoprosopa fasciata, cephalic aspect.

Exoprosopa fasciata, distal end, mesal aspect.

Exoprosopa fasciata, caudal aspect.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Cojicps Empi

420 421

E^'P's RhamphoTnyia

423 424 425

xoprosop*

426

Exoproiopa

427 428 4Se

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XVHI

-269] HEAD OF DIPTERA — PETERSOX 99

PLATE XIX

100

ILLINOIS BIOLOGICAL MONOGRAPHS

[270

Fig.

430.

Fig.

431-

Fig.

432.

Fig.

433-

Fig.

434-

Fig.

435-

Fig.

436.

Fig.

437-

Fig.

438.

Fig.

439-

Fig.

440.

Fig.

441-

Fig.

442.

Fig.

443-

Fig.

444.

Fig.

445-

Fig.

446.

Fig.

447-

Fig.

448.

Fig.

449.

Fig.

450.

Fig.

451.

Fig.

452.

Fig.

453-

Fjg.

454-

Fig.

455-

Fig.

456.

Fig.

457-

Fig.

458.

EXPLANATION OF PLATE
Labium

Chloropisca glabra, caudal aspect.

CJiloropisca glabra, cephalic aspect.

Dolichoptis bifractus, mesal aspect.

Dolichopus bifractus, caudal aspect.

Dolichopus bifractus, lateral aspect.

Pipunculus cingulatus, caudal aspect.

Pipunculus cingulatus, cephalic aspect.

Borborus equinus, caudal aspect.

Borborus equinus, mesal aspect.

Sepsis violacea, caudal aspect.

Sepsis violacea, mesal aspect.

Eristalis tenax, mesal aspect.

Eristalis tenax, caudal view.

Eristalis tenax, distal end of theca, caudal aspect.

Ochthera mantis, caudal aspect.

Ochthera mantis, mesal aspect.

Calobata univitta, mesal aspect.

Calobata univitta, caudal aspect.

Coelopa vanduzeii, caudal aspect.

Coclopa vanduzeii, mesal aspect.

Sphyracephala brevicornis, caudal aspect.

Sphyracephala brevicornis, mesal aspect.

Occothca fenestralisf caudal aspect.

Oecothea fenestralis, mesal aspect.

Drosophila anipclophila, caudal aspect.

Drosophila ampelophila, mesal aspect.

Chrysomyza demandata, mesal aspect.

Chrysomyza demandata, caudal aspect.

Siphona geniculata, distal end, cephalic aspect.

ILIJXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Chrysomyza Sipnoni Chrytomyza

456 468 467

rETERSOX MEAD AND Mt)UTll PARTS OE DIPTERA ELATE XE\

271] HEAD OP DIPTER A — PETERSON 101

PLATE XX

102 ILLINOIS BIOLOGICAL MONOGRAPHS [272

EXPLANATION OF PLATE
Labium and other Parts

Fig. 459. Heteroneura flaviseta, caudal aspect.

Fig. 460. Heteroneura flaviseta, mesal aspect.

Fig. 461. Loxocera pectoralis, caudal aspect.

Fig. 462. Loxocera pectoralis, mesal aspect.

Fig. 463. Tetanocera pluuiosa, caudal aspect.

Fig. 464. Tetanocera plumosa, mesal aspect.

Fig. 465. Musca domestica, dorsal aspect of glossae.

Fig. 466. Musca domestica, caudal aspect.

Fig. 467. Musca domestica, mesal aspect.

Fig. 468. Archytas analis, caudal aspect.

Fig. 469. Archytas analis, mesal aspect.

Fig. 470. Scatophaga furcata, caudal aspect of mediproboscis.

Fig. 471. Scatophaga furcata, ventral aspect of distiproboscis.

Fig. 472. Scatophaga furcata, mesal aspect.

Fig. 473. Thelaira leucosona, caudal aspect.

Fig. 474. Thelaira leucosona, mesal aspect.

Fig. 475. Hydrotaea dentipes, caudal aspect.

Fig. 476. Hydrotaea dentipes, mesal aspect.

Fig. 477. Sarcophaga haemorrhoidalis, caudal aspect.

Fig. 478. Sarcophaga haemorrhoidalis, mesal aspect.

Fig. 479. Stoinoxys cal citrons, distal end, lateral aspect.

Fig. 480. Stomoxys calcitrans, distal end, mesal aspect.

Fig. 481. Lispa nasoni, distal end, mesal aspect.

Fig. 482. Bombylius major, cross-section thru pseudotrachea. (After

Dimmock.)

Fig. 483. Ochthera mantis, cross-section thru pseudotrachea.

Fig. 484. Musca (Calliphora) vomitoria, cross-section thru pseudotrachea

(After Dimmock.)

Fig. 485. Musca (Calliphora) vomitoria. an enlarged pseudotrachea. (After

Dimmock.)

Fig. 486. Oncodcs costatus, entire mouth-parts, caudal aspect.

Fig. 487. Oncodes costatus, entire mouth-parts, lateral aspect.

Fig. 488. Olfersia ardeae, distal end, lateral aspect.

Fig. 489. Siniuliuni venustuvi, cephalic aspect of the labrum.

Fig. 490. Gastrophilus equi, entire mouth-parts, caudal aspect.

Fig. 491. Gastrophilus equi, sagittal section thru mouth-parts.

Fig. 492. Gastrophilus equi, entire mouth-parts, cephalic aspect.

IfJJXOIS BIOLOCIC.IL M0N(X7RAPHS

J'OLUME 3

PETERSON II I'M) AND MOUTH PARTS OF DIPTERA PLATE XX

273] HEAD OF DIPTERA— PETERSON 103

PLATE XXI

104

ILLINOIS BIOLOGICAL MONOGRAPHS

[274

EXPLANATION OF PLATE
Epipharynx and Hypopharynx and Associated Parts

Hypothetical type, lateral aspect.
Tabanus giganteus, female, lateral aspect.
Tabanus giganteus, male, lateral aspect.
Tabanus giganteus, female, caudal aspect.
Siniulium venustum, female, lateral aspect.
Sititulium venustum, female, caudal aspect.
Trichocera bimacula, lateral aspect.
Trichocera bimacula, caudal aspect.
Dixa clavata, lateral aspect.
Dixa clavata, caudal aspect.
Tipula bicornis, lateral aspect.
Psorophora ciliata, female, lateral aspect.
Psorophora ciliata, female, caudal aspect.
Geranomyia canadensis, lateral aspect.
Liinnobia iiinnatura, lateral aspect.
Rhyphus punctatus, lateral aspect.
Rhyphus punctatus, caudal aspect.

Fig.

493.

Fig.

494-

Fig.

495-

Fig.

496.

Fig.

497-

Fig. 498

Fig.

499.

Fig.

500.

Fig.

SOI.

Fig.

502.

Fig.

503-

Fig.

504.

Fig.

505.

Fig.

S06

Fig.

507.

Fig.

508

Fig.

509

ILLINOIS BIOLOGICAL MOXOGRAPHS

VOLUME 3

Psorophora » Pcoropbon

504 505

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XXI

275] HEAD OF DIPTERA — PETERSON 105

PLATE XXII

106 ILLINOIS BIOLOGICAL MONOGRAPHS [276

EXPLANATION OF PLATE
Epipharyxx and Hypopharynx and Associated Parts

Fig. 510. Rhabdophaga strohiloides, caudal aspect.

Fig. 511. Rhabdophaga strobiloides, lateral aspect.

Fig. 512. Sciara varians, caudal aspect.

Fig. 513. Sciara varians, lateral aspect.

Fig. 514. Periplaneta orientalis, clypeus, labrum, and epipharynx spread out, ental

aspect.

Fig. 515. Melanoplus dijfcrcntiaUs, clypeus, labrum, and epipharynx spread out,

ental aspect.

Fig. 516. Gryllus pciinsylvanicns, right-half of clypeus, labrum, and epipharynx,

cephalic and caudal aspects.

Fig. 517. Proiiiachns vertebratus, lateral aspect.

Fig. S18. Promachiis vertebratus, epipharynx and labrum, caudal aspect.

Fig. 519. Promachus vertebratus, caudal aspect.

Fig. 520. Leptis vertebrata, lateral aspect.

Fig. 521. Culicoides sanguisugus, lateral aspect.

Fig. 522. Bibio femoratus, caudal aspect.

Fig. 523. 'Bibio femoratus, lateral aspect.

Fig. 524. Dolichopus bifractus, caudal aspect.

Fig. 525. Leptis vertebrata, caudal aspect.

Fig. 526. Bibiocephala elegantula, caudal aspect.

Fig. 527. Bibiocephala elegantula, lateral aspect.

Fig. 528. Dolichopus bifractus, lateral aspect.

ILLINOIS BIOLOGIC.il MOXOGRAPHS

VOLUME 3

Dolichopus

524

Leptis

525

PETERSON lli:.\l) WD MOl'lli PARTS OF DIPTERA PLATE XXII

277] HEAD OF DIPTERA— PETERSON 107

PLATE XXIII

108 ILLINOIS BIOLOGICAL MONOGRAPHS [278

EXPLANATION OF PLATE
Epipharynx and Hypopharynx and Associated Parts

Fig. 529. Psychoda alhipennis, lateral aspect.

Fig. 530. Psychoda albipennis, caudal aspect.

Fig. 531. CJiironoiiius fcrrugincovittatus, lateral aspect.

Fig. 532. CliironoDitis fcrrngincovittatus, caudal aspect.

Fig. 533. Psilocephala hacmorrhoidalis, lateral aspect.

Fig- 534- Psilocephala hacmorrhoidalis, caudal aspect.

Fig. 535. Mydas clavatus, lateral aspect.

Fig. 536. Mydas clavatus, caudal aspect.

Fig. 537. Scenopinus fenestralis, caudal aspect.

Fig. 538. Scenopinus fenestralis, lateral aspect.

Fig. 539. Lonchoptera liitea, lateral aspect.

Fig. 540. Aphiochaeta agarici, caudal aspect.

Fig. 541. Lonchoptera lutea, caudal aspect.

Fig. 542. Platypcza velutina, caudal aspect.

Fig. 542a. Platypeca velutina, lateral aspect.

Fig. 543. Eulonchus tristis, lateral aspect.

Fig. 544. Aphiochaeta agarici, lateral aspect.

Fig. 545. Stratiomyia apicula, lateral aspect.

Fig. 546. Stratiomyia apicula, caudal aspect.

Fig. 547. Enipis clausa, lateral aspect.

Fig. 548. Empis clausa, caudal aspect.

Fig. 549. Exoprosopa fasciata, lateral aspect.

Fig. 550. Exoprosopa fasciata, caudal aspect.

ILLIXOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Empis

548

lixoprosopa ICvopTosopa

549 550 (g)

n: ri-.RSox ukad axd mouth parts of diptera plate xxiii

279] HEAD OF DIPTERA— PETERSON 109

PLATE XXIV

110 ILLINOIS BIOLOGICAL MONOGRAPHS [280

EXPLANATION OF PLATE
Epipharynx and Hypopharynx and Associated Parts

Fig. 551. Calohata univitta, caudal aspect.

Fig. 552. Calobata univitta, lateral aspect.

Fig. 553- Saproniyca vulgaris, lateral aspect.

Fig- 554- Sapro})iyza vulgaris, caudal aspect.

Fig- 555- Chloropisca glabra, caudal aspect.

Fig. 556. Chloropisca glabra, lateral aspect.

Fig. 557. ChrysoDiyza deinandata, caudal aspect.

Fig. 558. Chrysomyca deinandata, lateral aspect.

Fig. 559. Coelopa vanduzeii, caudal aspect.

Fig. 560. Coelopa vanduzeii, lateral aspect.

Fig. 561. Pipunculus cingulatus, caudal aspect.

Fig. 562. Pipunculus cingulatus, lateral aspect.

Fig. 563. Drosophila anipelophila, caudal aspect.

Fig. 564. Drosophila anipelophila, lateral aspect.

Fig. 565. Borborus equinus, lateral aspect.

Fig. 566. Borborus equinus, caudal aspect.

Fig. 567. Borborus equinus, hypopharynx united with labium, caudal aspect.

Fig. 568. Chyroinya concolor, caudal aspect.

Fig. 569. Chyroinya concolor, lateral aspect.

Fig. 570. Loxocera pectoralis, caudal aspect.

Fig. 571. Loxocera pectoralis, lateral aspect.

Fig. 572. Euarcsta aequalis, caudal aspect.

Fig. 573. Euaresta aequalis, lateral aspect.

Fig. 574. Ochthera mantis, lateral aspect.

Fig. 575. Ochthera mantis, caudal aspect of the labrum.

Fig. 576. Ochthera mantis, caudal aspect of the epipharynx.

Fig. 57/. Ochthera mantis, caudal aspect.

Fig. 578. Desmomctopa latipes, lateral aspect.

Fig. 579. Desmomctopa latipes, caudal aspect.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Euaresia

Euareata

Ochlhera

Ochihera

Desmomeiopa

572

673

674

676

677

678

679

PETERSON HEAD AND MOUTH PARTS OF DIPTERA PLATE XXIV

281] HEAD OF DIPTER A — PETERSON 111

PLATE XXV

112 ILLINOIS BIOLOGICAL MONOGRAPHS [282

EXPLANATION OF PLATE
Epipharynx and Hypopharyxx and Associated Parts

Fig. 580. Occothca fenestralis, lateral aspect.

Fig. 581. Oecothca fenestralis, caudal aspect.

Fig. 582. Sepsis violacea, lateral aspect.

Fig. 583. Sepsis violacea, caudal aspect.

Fig. 584. Tetanocera pluinosa, lateral aspect.

Fig. 585. Sphyracephala brevicornis, lateral aspect.

Fig. 586. Tetanocera plumosa, caudal aspect.

Fig. 587. Eristalis tenax, caudal aspect.

Fig. 588. Eristalis tenax, lateral aspect.

Fig. 589. Hetcroneura flaviseta, lateral aspect.

Fig. 590. Hcteroneura flaviseta, caudal aspect.

Fig. 591. Conops brachyrhynchiis, caudal aspect.

Fig. 592. Conops bracliyrJiynchns, lateral aspect.

Fig. 593. Scatophaga furcata, lateral aspect.

Fig. 594. Scatophaga furcata, caudal aspect.

Fig. 595. Thelaira leucosona, lateral aspect.

Fig. 596. Thelaira leucosona, caudal aspect.

Fig- 597- Hydrotaea dentipcs, lateral aspect.

Fig. 598. Hydrotaea dentipes, caudal aspect.

Fig. 599. Stomoxys calcifrans, lateral aspect.

Fig. 600. Musca domestica, lateral aspect.

Fig. 601. Musca domestica, caudal aspect.

Fig. 602. Sarcophaga hacmorrhoidalis, lateral aspect.

Fig. 603. Sarcophaga haemorrhoidalis, caudal aspect.

Fig. 604. Archytas analis, lateral aspect.

Fig. 605. Archytas analis, caudal aspect.

Fig. 606. Olfersia ardeae, lateral aspect.

ILLINOIS BIOLOGICAL MONOGRAPHS

VOLUME 3

Archytas ArchytM Ollersla

604 606 eoe

PETERSON HEAD AXD xMOUTH PARTS OF DIPTERA PLATE XXV

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