LSHTM
\
PUBLICATIONS OF THE UNIVERSITY OF MANCHESTER
BIOLOGICAL SERIES.— No. 1.
The Hoitse Fly
Sherratt & Hughes
Publishers to the Victoria University of Manchester
Manchester : 34 Cross Street
London: 33 Soho Square, W.
The House Fly
Musca domestica, Linnaeus
A Study of its Structure, Development,
Bionomics and Economy
BY
C. GORDON HEWITT, D.Sc.
Dominion Entomologist, Ottaiva, Canada, and late Lecturer in Economic
Zoology in the University of Manchester
At
MANCHESTER
the University Press
1910
University of Manchester Publications
No. LII.
PREFACE.
The appearance of a volume of this form needs, I feel,
some explanation. When first I expressed the intention of
publishing the results of my study of the House-fly in parts
as they were completed, it was suggested to me that, as the
separate parts of the monograph would appear at different
times and therefore in different volumes of the Quarterly
Journal of Microscopical Science, a useful purpose would be
served if, on the completion of the work, I were to have the
separate parts bound and published in volume form. Such
is my apology for the appearance of what, obviously, is
by no means a perfect production from a publisher's stand-
point. Sir Ray Lankester, K.C.B., the Editor of the
Q.J .M.S., kindly allowed me to obtain two hundred copies
of the letterpress and plates of each part, the three parts
appearing in 1907, 1908 and 1909 respectively. The number
of copies of this edition of the monograph is, therefore, very
limited. The Manchester University Press has been good
enough to undertake the re-publication of these reprints in
a volume, and has given me an opportunity of adding some
fresh introductory matter as well as appendices giving
additional facts and a rdswmd of such work as did not strictly
come within the scope of the monograph; there are also
included certain matters of practical importance. My
thanks are due to the Press Committee for overlooking the
clumsiness of the form in its wish to make my work more
accessible to students of the subject. In view of the foregoing
facts I feel that my readers will pardon the defects of
appearance, such as the numbering of the figures, etc., which
are the inherent drawbacks of the parts not being immediately
consecutive to each other at the time of their original
vi.
PREFACE
appearance. For the sake of reference an index lias been
prepared and a separate pagination has been given above
the original pagination, which was retained for the sake of
the cross references in the text of the separate parts. The
original numbering of the plates has been retained, and as
the plates of each part are to be found immediately following
that part no difficulty should be experienced in referring to
the figures.
This work was carried out while I was a member of the
Zoological Staff of the Manchester University, and I should
like again to express my sincere thanks to my former
teacher, Prof. Sydney J. Hickson, and to the Council of the
University for the opportunities which they gave me for
the prosecution of my studies. I would also take this
opportunity of thanking Sir Ray Lankester for his help in
the matter of publication.
C. Gordon Hewitt.
CONTENTS.
Preface. Introduction.
Part I. Anatomy of the Fly. page
I. Introduction 1
II. Methods 5
IK. External Structure: —
1. Head ... 6
2. Thorax 12
3. Abdomen .'. 20
IV. Internal Structure: —
1. Muscular System 21
2. Nervous System ... 22
3. Alimentary System 26
4. Inspiratory System 30
5. Vascular System and Body Cavity 35
6. Reproductive System 36
V. Internal Structure of Head 41
VI. Summary of Part 1 45
VII. Literature 48
Vlli. Explanation of the Plates 22—26 50
Part II. The Breeding Habits, Development, and the Anatomy of
the Larva.
I. Introduction 56
II. Breeding Habits 57
III. Factors and Kate of Development 60
IV. Development : - -
1. Copulation 65
2. Egg 66
3. Larva 66
4. Pupa 68
CONTENTS
PAGE
V. The Anatomy of the Larva: —
1. External Structure 70
2. Muscular System 73
3. Nervous System 79
4. Alimentary System 83
5. Respiratory System 88
6. Vascular System and Body Cavity 90
7. Imaginal Discs 92
VI. Summary of Part II 95
VII. Literature 98
VIII. Explanation of Plates 30—33 101
Part III. The Bionomics, Allies, Parasites, and the Relations of
M. domestica to Human disease.
I. Introduction 107
II. Distribution of M. domestica 108
III. Flies occurring as Co-inhabitants of Houses with
M. domestica or as visitants 110
IV. Physiology: —
1. Influence of Food, Temperature and Light... 121
2. Hibernation 122
3. Flight , ... 123
4. Regeneration of Lost Parts 124
V. Natural Enemies and Occasional Parasites 125
1. Chernes nodosus, Schrank 126
2. Acarina or Mites borne by House-flies ... 128
3. Fungal parasite — Empusa muscae, Cohn ... 130
VI. True Parasites : —
1. Flagellata — Herpetomonas muscae-domes-
ticae 133
Crithidia muscae-domesticae . . . 138
2. Nematoda — Habronema muscae 139
3. Dissemination of Parasitic Worms 141
CONTENTS
ix.
PAGE
VII. Dissemination of Pathogenic Organisms by M.
domestica and its non-Blood-sucking Allies 142
1. Typhoid Fever 144
2. Anthrax 153
3. Cholera 155
4. Tuberculosis 157
5. Ophthalmia 158
6. Plague ... 160
7. Miscellanea 161
VIII. Flies and Intestinal Myiasis 163
IX. Literature 164
X. Appendix on the Winter Breeding of M. domestica 171
XI. Corrigendum 172
XII. Explanation of Plate 22 173
XIII. Appendix A. Further Observations on the Dissem-
ination of Bacterial and other Organisms
by M. domestica 174
1. The Relation of Flies to Summer Diarrhoea
of Infants 174
2. Bacteria and Fungal Spores carried by M.
domestica 178
3. Flies and Milk .. 182
4. Flies in Military Camps 183
XIV. Appendix B. Additional Observations on the
Breeding Habits of Musca domestica . . . 183
XV. Appendix C. Preventive Measures 185
XVI. Appendix D. A Further Parasite of M. domestica 186
XVII. Additional Literature 188
INTRODUCTION.
" Familiarity breeds contempt." This, until a few years
ago, was certainly the case with regard to man's attitude
towards the house-fly, and it not infrequently happens that
some animals are so common that they are not considered
of sufficient scientific interest to be worthy of study. It is
unfortunately too often considered by zoologists, probably
unknowingly, that the ultimate value of the careful study
of an animal is directly proportionate to its rarity. A
little reflection will afford other instances of the neglect
of common creatures.
Of all animals associated with man, none is more common ;
he has no attendant more constant. Wherever he has
travelled the ' domestic ' fly has accompanied him, by water
and by land ; whether he travels on the modern ocean liner,
on the Canadian Pacific trans-continental express making
its three thousand miles journey, or in the humble electric
car from street to street, house-flies are his constant
companions.
Recent investigations, however, have shown that we must
substitute " fear " for " contempt " in the old adage in the
case of this ubiquitous companion. The house-fly is not " a
wholesome little creature " as it was described by one whose
scientific knowledge is as profound as it is accurate (I refer
to an editorial published in a well-known and much-
advertised English journal commenting on a lecture that
was delivered by me a few years ago on the dangers of the
house-fly), but it is an animal which normally bears on its
feet, legs and body and leaves in its tracks the organisms
productive of decay and not infrequently disease. This is
xii.
INTRODUCTION
the animal which not only constantly dines with us, tests
the wkolesonieness of our food and of the food of our
children, but also regales its palate with the juices of the
excreinental products of various animals, including man.
Constant in its attendance upon us in our sleep — which is
often disturbed — and when awake, we are apt to lose sight
of that side of the fly's life, of its double life, which is
passed out of doors, most frequently in search of a place to
deposit its eggs, which is equivalent to saying in search of
excrement or decaying vegetable substances.
It has been tried and found guilty in spite of the
questionings of those who maintain the doctrine that every
creature performs some useful purpose. Undoubtedly the
fly does, for where there is an abundance of filth, there will
the flies gather together, there will they multiply and
increase. Its function to-day is nothing more or less than
a danger signal to indicate insanitary conditions and the
presence in the neighbourhood of decaying or excremental
substances. Abolish these and the breeding places of the
flies will be eradicated; maintain them and this potential
disease carrier will be retained within our houses.
The importance of the house-fly as a disease carrier is
considered at length in the third part of this monograph
and in Appendix A., and I have considered briefly the
preventive and remedial measures in Appendix C. It will
never become a rare insect, and the vision of my friend Sir
James Crichton Browne of the aged person showing the
wondering child the only specimen existing of the house-fly
in the British Museum will, unfortunately, never be
realised ; but there is no reason why, by the adoption of such
sanitary measures as the breeding habits of the insect have
indicated to be necessary, it should not be considerably
decreased in numbers and rendered impotent as a disease
carrier. We need such determination and zeal on the part
of public bodies as that displayed by the New York
INTRODUCTION
Xlll.
Merchants' Association to abate this dangerous insect in our
midst. The subjection of the house-fly is as possible as that
of mosquito, compared with which it is equally dangerous
and far more so in populated areas. A complete study of
the life-history of the larvae and of the breeding habits of
the fly has given the key to the methods of prevention and
remedy. The solution of the evil has been given ; it remains
only for medical officers of health and those in whose hands
the health and well-being of the people is entrusted to apply
these results. Sufficient words of advice and warning have
been spoken, action is needed.
C. GORDON HEWITT.
Ottawa,
January, 1910.
The House Fly
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-ELY. 395
The Structure, Development, and Bionomics of
the House-fly, Musca domestica, Linn.
Part I.— The Anatomy of the Fly.
By
C. Gordon Hewitt, UI.Sc,
Lecturer in Economic Zoology, University of Manchester.
With Plates 22—26.
Contents.
page
I. Introduction .
395 (1)
II. Methods
399 (5)
III. External Structure.-
-1.
Head
400 (6)
2.
Thorax
406 (12)
3.
Abdomen
414 (20)
IV. Internal Structure.
-1.
Muscular System
415 (21)
2.
Nervous System
416 (22)
3.
Alimentary System .
420 (26)
4.
Respiratory System
424 (30)
5.
Vascular System and Body
Cavity .
429 (35)
6.
Reproductive System
430 (36)
V. Internal Structure of Head ....
435 (41)
VI. Summary
439 (45)
VII. Literature
442 (48)
I. Introduction.
This paper is intended to be the first of a series of three
dealing with the anatomy, development and bionomics of the
House-fly, Musca domestica, L. The second part will
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396
0. GORDON HEWITT.
include an account of the anatomy of the larva, its develop-
ment and the breeding habits of the fly ; the series will be
concluded with an account of the bionomics of the fly with
special reference to its relations with man.
The term " House-fly " to the zoologist refers only to one
insect — Musca domestica of Linnaeus, but to the popular
mind it includes insects, not different species only, but differ-
ent families of Diptera. The Eoot Maggot fly (Pi. 22, fig. 2),
Anthomyia radicum, L., sometimes occurs commonly in
houses. Homalomyia canicularis, L. (fig. 3), often
called the Small House-fly, is a very common inhabitant of
houses. The latter species is smaller than M. domestica,
and on this account they are frequently supposed to be young
specimens of the latter species by persons who are ignorant
of the fact that growth takes place during the larval stage
and not after the exclusion of the imago. Stomoxys
calcitrans, L. (fig. 4), is found in houses, especially in the
autumn. It is frequently mistaken for M. domestica, and
as it is one of the blood-sucking species (See Austen,
1906), the pernicious habit is attributed to the harmless
M. domestica either on account of the supposed ill-nature
of the latter or the influence of some change in the
weather.1
In addition to these, other species of flies occur in houses
but these will be considered in a later part. Reference has
been made here to the various species inhabiting houses to
show that the term " House-fly " as ordinarily used is rather
an inclusive one.
The House-fly has received some attention from naturalists
in all ages. Reaumur (1738), De Geer (1752-78) and Bouche
(1834) have all included a short account of this insect in their
classical memoirs. They do not contribute much to our
knowledge of the anatomy and development of the fly. The
1 Stomoxys calcitrans can be readily distinguished from M. domes-
tica by the awl-like proboscis which projects forwards from beneath the head.
It has a more robust general appearance, a dark spotted abdomen, and its
flight is more steady.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 397
most complete of these etirly accounts is that of Keller
(1790) which is illustrated by several striking plates. He
gives an interesting account of the development and breed-
ing habits, but in attempting to describe the anatomy he was
not so successful as exemplified by his mistaking the brown
testes for kidneys. In 1874 Packard wrote what is up to the
present time the most complete account of the development
of this species, and in 1880 Taschenburg, in his ' Praktische
Insektenkunde ' gave a good popular account of the insect.
Howard has more recently (1898 and 1902) contributed to
our knowledge of the developmental history.
No complete account of the anatomy of this insect has yet
been published. A short popular account by Samuelson and
Hicks (1860) though interesting is very superficial, and con-
tains much that is inaccurate. Macloskie (1880) has published
an account of the proboscis of M. domestica, and the foot
has been made an object of study by several workers, chief
of whom are Hep worth (1854), and Merlin (1895 and 1905),
who correctly described the glandular hairs of the pulvilli.
Wesche has recently (1906) described the genitalia of both
sexes, but his description and figures are inaccurate. An
interesting account of the copulation of the fly has been pub-
lished by Belese (1902), in which he briefly describes the
reproductive organs, his work will be referred to later.
Lowne's monograph (1895) on the Blow-fly (Calliphora
ery throcephala), which is an elaboration of his previous
memoir (1870) is the only complete account which has been
published on Muscid anatomy. The result of my study of
the anatomy of M. domestica, which was begun in 1905,
and is being continued in the Zoological Laboratories of the
Manchester University, has been to make it apparent that
much of Lowne's work needs confirmation.
Musca domestica was first described by Linnaeus (1758),
his description is as follows : —
" Antennis plumatis pilosa nigra, thorace lineis 5 obsoletis
abdomine nitidulo tessellato : minor. Habitat in Europa?
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398
0. GORDON HEWITT.
domibus, etiam Americae. Larvae in simo equinae. Pupae
parallele cubantes."
Later Fabricius described it more fully in his ' Genera
Insectorum.' The House-fly, together with the Blowfly, and
the blood-sucking flies Stotnoxys and Grlossina belongs to
the family Muscidae, which is characterised by having the
terminal joint of the antenna — the arista always combed or
plumed and by the absence of large bristles or macrochaetae
on the abdomen. The Muscidae, together with the Antho-
myidae and Tachinidae constitute the group Muscidae
calypteratae are characterised by the possession of squamae,
small lobes at the bases of the wings which cover the halters.
In the acalyptrate muscids the squamae are absent or rudi-
mentary. These two groups belong to the suborder Cyclor-
r hap ha, one of the two primary divisions of the Diptera.
The Cyclorrhapha have coarctate pupae, the pupal case
being formed by the hardening of the last larval skin, and
the flies escaping through a circular orifice formed by the fly
pushing off the end of the pupa by means of an inflated sac-
like organ — the ptilinium which is afterwards withdrawn into
the head, its presence being marked by a frontal crescentic
opening the lunule. The other sub-order the Orthorrhapha
have obtected pupae.
The most complete specific description of Musca domes-
tic a has been given by Schiner (1864), of which the follow-
ing is a free translation : —
" Frons of male occupying a fourth part of the breadth of
the head. Frontal stripe of female narrow in front, so broad
behind that it entirely fills up the width of the frons. The
dorsal region of the thorax dusty grey in colour with four
equally broad longitudinal stripes. Scutellum grey, with
black sides. The light regions of the abdomen yellowish,
transparent, the darkest parts at least at the base of the
ventral side yellow. The last segment and a dorsal line
blackish brown. Seen from behind and against the light the
whole abdomen shimmering yellow, and only on each side of
the dorsal line on each segment a dull transverse band. The
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 399
lower part of the face silky yellow, shot with blackish brown.
Median stripe velvety black. Antennas brown. Palpi black.
Legs blackish brown. Wings tinged with pale grey with
yellowish base. The female has a broad velvety black, often
reddishly shimmering frontal stripe, which is not broader at
the anterior end than the bases of the antennas, but becomes
so very much broader above that the light dustiness of the
sides is entirely obliterated. The abdomen gradually be-
coming darker. The shimmering areas on the separate
segments generally brownish. All the other parts are the
same as in the male."
The mature insects measure from 6-7 mm. in length and
13-15 mm. across the wings. Flies which have been starved
during the larval stage or subjected to adverse conditions are
generally smaller in size.
II. Methods.
All the details of the anatomy which are about to be
described have been studied by means of dissections. The
dissections were made on both fresh and preserved material
under a Ziess' binocular dissecting microscope with magnifi-
cations varying from 25-65 diameters. Serial sections have
been made to confirm the dissections and to study the histo-
logical details.
Perfect series of sections of the whole fly were hard to
obtain on account of the somewhat brittle nature of the in-
ternal chitinous structures. These internal chitinous skeletal
elements caused the greatest trouble as they were apt to
damage the internal anatomy. Celloidin sections were not a
great improvement on those cut in paraffin. The best results
were obtained by fixing the flies from 12-24 hours in
Henning's solution, which is — Nitric acid 16 parts, chromic
acid ('5 per cent.) 16 parts, corrosive sublimate saturated in
60 per cent, alcohol 24 parts, picric acid saturated in water
12 parts, and absolute alcohol 42 parts, washing out with
iodine alcohol. This not only fixes, but to a certain extent,
though not completely, softens the chitin. They should not
(61
400
C. GORDON HEWITT.
be imbedded too long or the chitin becomes brittle again.
Serial sections made of recently emerged imagines before the
chitin has hardened give good results. Other fixing agents
used were Perenyi, RabPs Chi-omoformic, Picro-formal
(Bourn's solution), Glacial acetic acid, and absolute alcohol.
Of the various stains which were used the most satisfactory
were Heidenhain's Iron-ha3matoxylin, Brazilin,1 and Dela-
field's Hematoxylin. With the last stain perfect results
were obtained by overstaining and differentiating with acid-
alcohol.
The structure of the thoracic ganglion was studied by
means of reconstructions. The method employed was as
follows : — The sections were drawn by means of the camera
lucida on Bristol board of a thickness proportional to the
magnification. They were afterwards cut out and seccotined
together. The resulting model was trimmed and soaked in
melted paraffin, taken out and dipped several times till a thin
coating of paraffin covered the model. This was then trimmed
down to the original size, all the interstices having been
filled by the paraffin. After a coating of graphite it was
electrotyped with copper. In this way a permanent model
was obtained.
III. External Structure.
1. The Head Capsule.
The head capsule of M. domestica presents great modi-
fications when compared with the typical insect head. Con-
siderable difficulty is experienced in explaining its structure
in the morphological terms employed in the simpler orders
of insects. Lowne did not lessen the difficulty in describing
the head of the blowfly by the invention of new terms of
little morphological value. The head of the fly is strongly
convex in front (PI. 23, fig. 1), the posterior surface being
almost flat and slightly conical. For the sake of clearness the
1 See Hickson, S. J., " Staining with Brazilin," • Quart. Journ. Micr. Sci.,'
vol. 44, pp. 469-471, 1901.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 401
composition of the head capsule will be described from
behind forwards. The occipital foramen occupies a median
slightly ventral position on the posterior surface. It is
surrounded by the occipital ring, the inner margin of which
projects into the cavity of the head. From the sides of the
inner margin of the occipital ring two short chitinous bars
bend inwards and approach each other internally, forming a
support — the jugum for the tentorial membrane. On each side
of the occipital ring below the jugum a small cavity occurs
into which a corresponding process from the prothorax fits,
forming a support for the head.
The occipital ring is surrounded by the four plates, which
make up the sides and back of the head capsule. On the
ventral side, between the occipital ring and the aperture
from which the proboscis depends, a median basal plate, the
gulo-mental plate, represents the fused gula and basal por-
tions of the greatly modified second ruaxillaa. The occipital
segment is bounded laterally by the genee (Lowne's para-
cephala) and dorsally by the epicranium. These parts have
been divided by systematists into so many regions that a
somewhat detailed description will be necessary to make
their boundaries clear.
The genge bear the large compound eyes which occupy
almost the whole of the antero-lateral regions of the head.
On the posterior flattened surface of the head the genas are
flat, and extend from the gulo-mental plate to the epicranial
plate, the sutures of the latter being vertical. On the dorsal
side each sends a narrow strip between the inner margin of
the eye and the epicranium ; this stx*ip surrounds the eye
and meets the ventral portion of the gena ; it is of a silver to
golden metallic lustre. On the ventral side below the eye
each gena bounds the proboscis aperture laterally ; a number
of stout bristles arise from this margin and also from its
antero-lateral region, which is often spoken of as the "jowl."
In the anterior region, where the genaa are in contact with
the clypeus, there are two prominent ridges beai'ing strong
setae ; these are usually known as the " facialia."
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402
C. GORDON HEWITT.
The epicraninm (epiceplialon of Lowne) on the posterior
surface of the head is flat. On the anterior surface it is
convex, and divided into a number of regions. On the top
of the head between the eyes it is called the vertex. This
contains the three ocelli situated on a slightly raised ocellar
triangle, which is surrounded by a second triangle, the
vertical triangle. The median region in front of and below
the vertex is the frons. In the middle of this there is a
black frontal stripe. In the male the eyes are only narrowly
separated by the frontal stripe. In the female the frontal
stripe widens out on the vertex. This character provides a
ready means of distinguishing the male from the female, as
the result of it is that in the male the eyes are close together
on the dorsal side being separated by about one fifth of the
width of the head, whereas in the female the space between
the eyes is about one third the width of the head. The
edges of the genaa bordering on the frons bear each a row of
stout setaa — the fronto-orbital bristles. The antennas arise
from the lower edge of the frons. Each antennaa consists of
three joints and the arista. The two proximal joints are
short and compose the "scape." The third joint, the
fla»-ellum, is longer, somewhat cylindrically prismatic in
shape, and hangs vertically in front of the clypeus. It is
covered with sensory setas, and contains two pits of sensory
function (olfactory, I believe). From the upper side the
plumose arista arises. This probably represents the terminal
three joints of the antenna. The lower edge of the frons
represents the anterior margin of the epicranium.
The rest of the facial region is composed of the clypeus or,
as it is usually called, the face — a convenient term, but one
which hides its true moi-phology. The face is depressed,
and is covered by the flagellae of the antennae. Between the
upper and lateral edges of the face and the lower edge of
the epicranium a crescentic opening, the lunule, marks the
invagination of the ptilinium. The cpistomium is a narrow
strip below the face bounding the anterior edge of the
proboscis aperture.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP UOUSE-FLY. 403
The Skeleton of the Proboscis. — The proboscis of
M. douiestica is very similar to that of the blowfly, which
has been described by Kraepeliu (1880) and Lowne (1895),
though the results of these authors differ in many details.
My study of M. domestica confirms Kraepelin's results, and
as Lowne's is the only complete account of the muscid head
a full description of its internal and external anatomy will
be given in this paper.
Lowne regards the greater part of the proboscis as being
developed from the first maxillaa and not from the labium
or fused, second maxillas, which is the usually accepted view
and one which I support on morphological grounds. On
account of his exceptional conclusion he refuted the com-
monly accepted terms for the vaiuous parts and invented
new ones. It will be necessary for the sake of descriptive
clearness to refrain from constant reference to these or any
discussion as to their value.
The proboscis consists of two parts, a proximal mem-
branous conical portion — 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,
haustellum, and oral lobes.
The rostrum (fig. 13, Bos.) is attached to the edges of
the proboscis aperture, that is to the epistomium, genas, and
the gulo-mental plate. It has the shape of a truncated cone,
and bears on the anterior side a pair of palps, which bear
sensory setae of two sizes.
The haustellum (fig. 13, H.), or proboscis proper, is
attached to the distal end of the rosti-um. The posterior
side is formed by a convex, somewhat heart-shaped sclerite
— the theca (figs. 1 and 3, th.) which probably represents
a portion of the labium. The lower angle of the theca
is incised by a semicircular sinus. By means of this the
theca rests on a triradiate chitinous sclerite — the f urea, which
consists of a median, slightly convex rod (fig. !,/•)> from the
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404
C. GORDON HEWITT.
anterior end of which two arms diverge and form the chief
skeletal structures of the oral lobes. The lower end of the
theca rides on this structure; the bottom of the sinus resting
on the median rod, and the two-pointed lateral terminations
of the theca rest on the arms. In this manner these pro-
cesses, in a state of repose, keep the arms of the f urea closely
approximated. The result of this will be seen later in study-
ing the musculature of the proboscis.
The sides of the haustellum are membranous. On its
anterior face, in a groove formed by the overlapping mem-
branous sides, lie the labrum-epipharynx and labium-hypo-
pharynx. The labrum-epipharynx (figs. 1 and 3, l.ep.) is
attached at its proximal end to the membranous rostrum, but
is incapable of a labral-like movement on account of its close
connection with the labium-hypopharynx. Two slightly-
curved, hammer-shaped apodemes (fig. 1, ap.) are attached
to the proximal end of the labium-epipharynx. They assist
in folding the proboscis during retraction, as will be shown
later. The labium-epipharynx is shaped like a blunt arrow-
head; the external surface is somewhat flattened. It is
composed of two pairs of sclerites, an outer pair enclosing an
inner pair, which form the pharyngeal channel. The edges
of the inner tube are connected by a groove with the hypo-
pharyngeal portion of the labium-hypopharynx, as shown
in fig. 3. The labium-hypopharynx (fig. 3) represents the
fusion of the hypopharynx with the greatly modified and
fused second maxillas or labium. It consists of a sclerite,
curved in section, having the chitinous hypopharyngeal tube
(fig. 3, hp.) fused to it along the upper half of its length.
The edges of the hypopharyngeal tube engage with those of
the inner pair of sclerites of the labium-epipharynx, as men-
tioned before. Distally the hypopharyngeal tube becomes
free from the labium, as shown in fig. 3, and ends in a point
where the lingual salivary duct opens.
Down each side of the labium-hypopharyngeal sclerite a
rod-like thickening runs. Distally these thickened margins
(paraphyses of Lowne) articulate with the discal sclerites.
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STRUCTURE, DEVELOPMENT, AND BTONOM1CS OP HOUSE-PLY. 405
The discal sclerites (fig. 1, ds.) are united at the posterior
end to form, when the oral lobes are expanded, a U-shaped
structure, with the limbs constricted in the middle where the
ends of the thickened margins of the labiutn-hypopharynx
articulate. They are sunk in deeply between the two oral
lobes at the base of the oral pit with the free ends of the U
anterior, these being spatulate and curved anteriorly.
The two oral lobes are normally connected by a bead and
groove attachment along their anterior edges, but under
pressure the connection is severed, and the oral disc presents
a heart-shaped instead of the normal oval appearance. The
oral lobes are covered on their upper aboral surfaces by
sensory setae, the large marginal setae being different in
structure from the rest. On the lower or oral surface a large
number of channels, the pseudotracheae (fig. 1, ps.) run from
the internal margins of the oral lobes to the external borders.
The channels of the pseudotracheae are kept open when the
lobes are extended by means of small incomplete chitinous
rings, which give the channels a ti'acheal appearance, hence
their name. Each of these incomplete rings has one end
bifid, and as the bifid ends alternate the opening into the
channel has a zigzag appearance. The number of pseudo-
trachese on each lobe is generally thirty-six, and they are
grouped in three sets. The anterior set of twelve all run
into a single large pseudotracheal channel running along the
anterior inner margin of the lobe, and a posterior set of
twenty-one all run into a channel running along the posterior
inner margin ; between these two sets three pseudotrachese
run direct into the oral aperture. The oral aperture lies at
the base of the small oral pit, which is a space kept open
between the oral lobes by means of the discal sclerites. The
pseudotracheae do not extend as far as the discal sclerites,
but on entering the oral pit the rings cease and the sides of
the channels are covered by overlapping teeth, which extend
back to the discal sclerites. Between the pseudotracheae the
membranous surface of each oral lobe is thrown into two
longitudinal sinuous ridges, and projecting up from the
VOL. 51, PART 3. — NEW SERIES. 31
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406
0. GORDON HEWITT.
bottom of the furrows are several papillae, generally four
or five to each interpseudotracheal area, of a gustatory-
nature — the gustatory papillae (figs. 1 and 18, gp.).
The Fulcrum. — This chitinous portion of the pharynx
(fig. 1, F.) lies on the lower part of the head and in the
rostrum. Kraepelin describes it as being shaped like a
Spanish stirrup iron. Its structure will be best understood
by referring to the figures. It consists of an outer portion,
which is U-shaped in section; the basal portion, which is
posterior and forms the floor of the pharynx (which Lowne,
unfortunately, terms the hypopharynx) is vertical when the
proboscis is extended. This basal portion is evenly rounded
at both ends, and at the sides of the upper end there is a
pair of processes — the posterior cornua (fig. 1, pc.) which
serve for the attachment of muscles. The sides of the
fulcrum are somewhat triangular in shape ; their upper
anterior portions are produced to form the anterior cornua
(a.c.) ; here the sides bend inwards at right angles, and
meet below the epistomium, upon which the fulcrum is
hinged. The fulcrum is therefore quadrilateral in section at
the upper proximal end, and trilateral at the lower distal end.
The basal portion (fig. 2, h.p.) forms the floor of the pharynx;
the roof of the pharynx is formed by another chitinous piece
(r.p.) with a median thickened raphe. This roof lies parallel
with the basal piece, and is fused with the sides of the
fulcrum. On the membranous wall of the pharynx, between
the labium-hypopharynx and the fulcrum, a small chitinous
sclerite (fig. 1, k.) is developed, which Lowne terms the
hyoid sclerite. It is U-shaped in section, and serves to keep
the lumen of the pharynx in this region distended.
2. The Thorax.
As in all Diptera the possession of a single pair of wings
has resulted in the great development of the mesothorax at
the expense of the other thoracic segments, consequently the
thorax is chiefly made up of the sclerites composing the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 407
mesothorax. The protliorax and metathorax compose very
small portions on the anterior and posterior faces respec-
tively. Seen from above the thorax is oviform with the
blunt end anterior and slightly flattened. Three transverse
sutures on the dorsal side mark the limits of the prescutum,
scutum, and scutellum of the mesothoracic segment ; the
mesothoracic scutellum forms the pointed posterior end, and
slightly overhangs the anterior end of the abdomen.
The Prothorax. — The prothoracic segment has been
reduced to such an extent that it is hopeless to attempt to
homologise all the separate sclerites with those of a typical
thoracic segment. To obtain a complete view of the pro-
thorax it is necessary to examine it from the anterior end
after the removal of the head. The following sclerites can
then be recognised. The prosternum is a median ventral
plate, quadrilateral in shape having the anterior end rounded
and broader than the posterior end. It does not occupy the
whole of the prosternal area, but is bounded by the prosternal
membrane. Internally a ridge runs to the posterior end of
the prosternum and bifurcates, each ridge running to the
posterior corners, to which two strong processes (the hypo-
tremata of Lowne) are attached. In front of the prosternum
there is a small saddle-shaped sclerite which, on account of
its position, may be called the interclavicle (the sella of Lowne).
Two lobes at its anterior end are covered with small pro-
cesses, probably sensory in function. A pair of small sclerites
is situated in front of these lobes ; these sclerites with the
interclavicle no doubt belong to the prosternum. The inter-
clavicle is ventral to the cephalothoracic foramen. The
jugulares (3ine jugulaires of Kunckel d'Herculais) are two
prominent pocket-shaped sclerites lying one on each side of
the cephalothoracic foramen, and having their convex faces
external. Lying immediately below each of the jugulares is
a small rod-like sclerite — the clavicle. The dorsal region of
the prothorax the pronotum (fig. 6 pr.n.) is formed by two
sclerites united in the median line, their dorsal sides being
curved. From the ventral side of the pronotum a pair of
(14)
408
0. GORDON HEWITT.
cliitinous apodemes project into the thoracic cavity. The
lateral regions of the pronotum are in contact with the
humeri and the prothoracic episterna. The humeri (Jiu.) are
a pair of strongly convex sclerites situated in the antero-
lateral region of the thorax. They are bounded above by the
prescutum of the mesothorax, internally and below by the
episterna of the prothorax, and externally by the lateral plate
of the mesosternum and the anterior thoracic spiracle. Its
inner concave surface serves for the attachment of the muscle
of the prothoracic coxa. The episterna {eps.') (epitrochlear
sclerites of Lowne) are comparatively large sclerites forming
the lateral regions of the prothorax. They ovei'hang the
attachments of the prothoracic limbs. The internal skeleton
of the prothorax consists of the two stout hollow apodemes —
the hypotremata mentioned previously. They arise from the
postero-lateral edges of the prosternum, and run obliquely
across the ventral edge of the anterior thoracic spiracle
where the hypotreme divides, the posterior branch runs up
the posterior margin of the spiracle, between the lateral plate
of the mesosternum and the peritreme (the chitinous ring
surrounding the spiracle), the anterior branch fuses with the
prothoracic episternum.
The Me so thorax. — The notum of the mesothorax occu-
pies the whole of the dorsal side of the thorax. It is com-
posed of the four sclerites to which Audouin (1824) gave the
name of prescutum, scutum, scutellum, and postscutellum.
The prescutum (prs.) forms the anterior part of the dorsal
region of the thorax. Its anterior portion bends down almost
vertically to unite with the pronotum. The anterior edge of
the prescutum is inflected after the pronotal suture, and is
produced in the median line into a small bifurcating process.
The prescutum is bounded laterally by the humerus and a
membranous strip — the dorso-pleural membrane. The scutum
(se.) is the largest of the mesonotal plates. It occupies the
whole of the median dorsal region of the thorax. Anteriorly
it is bounded by the prescutum, laterally by the alar membrane
and the lateral plate of the postscutellum, and posteriorly by
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 409
the scutellurn. From the lateral region of the scutum a pro-
cess projects forwards and downwards, and articulates with
the posterior portion of the wing-base (the metapfcerygium).
The scutellum (sctl.) is a triangular pocket-shaped sclerite
which overhangs the postscutellum and the base of the abdo-
men. The posterior surface of the thorax is chiefly composed
of the large postscutellum. This is made up of three pieces,
a median escutcheon-shaped plate (mpsc.) strougly convex to
the exterior, and two convex lateral plates (lp.sc). The lateral
plates are bounded below by the metasternum and spiracles,
and anteriorly by the pleural region of the mesothorax.
The mesosternum is a sclerite of considei'able size and forms
the keel of the thorax. It consists of a median ventral por-
tion (ms.) which is produced laterally to form two large
lateral plates (lp.). The median portion is bounded in front
by the presternum and the foramina of the anterior coxae, and
behind by the median coxal foramina. A short distance
behind the anterior end a depression in the mid-ventral line
extending to the posterior edge indicates a median inflection
forming the entothorax. The lateral regions of the posterior
margins of the mesosternum are inflected on each side to form
the entopleura. The lateral plates of the mesosternum form
the whole of the anterior portion of the pleural region ; each
is bounded in front by the humerus, spiracle, and prothoracic
episternum, and above by the dorso-pleural membrane, and
behind by the mesopleural membrane. The ventral side of
the lateral plate is continuous in front with the median plate
of the mesosternum, and behind is united by means of a
suture. The remaining portion of the mesopleural region is
made up of the episternum, epimeron, and two small sclerites
connected with the wing-base — the parapteron and costa.
The episternum (eps.") is situated behind the mesopleural
membrane and below the alar membrane, below and behind
it is bounded by the epimeron. Its surface is marked by two
convexities, the ampulla), the upper of the two corresponding
to Lowne's great ampulla of the blowfly. The dorsal side of
(16)
410
C. GORDON HEWITT.
the episternum is intimately connected with the sclerites1 of
the anterior portion of the wing-base.
The epimeron {ep.') is a triangular sclerite, and is bounded
below by the mesosternum and metasternum, behind by the
lateral plate of the postscutelluin, and above by the episternum
and alar membrane. The parapteron (pt.) is a sclerite situ-
ated at the top of the mesopleural membrane. The greater
portion of it is internal, only a small triangular portion can
be seen externally. Internally this is continued as a cruri-
form sclerite to which are attached important muscles con-
trolling the wings. The costa (ca.) is a small sclerite situated
on the dorsal mai'gin of the epimeron. The internal skeleton
of the mesothorax consists of the entothorax, entopleura,
mesophragrna, and the inflected edges of the episterna and
epimera. The entothorax is composed of a median vertical
plate subtriangular in shape, on the top of which a median
plate produced laterally into wing-like processes rests. On
this structure the thoracic nerve-centre lies. The entopleura
and the inflected edges of the episterna and epimera all serve
for the attachment of wing muscles. The mesophragma
(mph.) is a convex sclerite fused with the lower edge of the
postscutellum. Its posterior edge is incised in the middle
and forms the dorsal arch of the thoraco-abdominal foramen.
The Metathorax. — The largest sclerite of the greatly
reduced metathorax is the metasternum (mts.). It is a wing-
shaped sclerite with the narrow transverse portion situated
between the coxal foramina of the median and posterior pairs
of legs; the expanded lateral portions form the wall of the
thorax above the insertions of these legs. The edges of the
narrow transverse strip are inflected, and unite the lateral
portions of the metasternum. A trough-shaped longitudinal
fold — the metaf urea rests on the narrow transverse portion of
1 la this account the individual sclerites which compose the wing base will
not be described. Lowne has described them at great length for the blowfly,
and although the wing-base sclerites ofM. domestica differ slightly in shape
from those of Calliphora, Lowne's description of their relations holds good
for the former insect.
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STRUCT LJRH, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 411
the rnetasternurn. The posterior end of the metafurca bends
downwards and articulates with the posterior coxaa on each
side. The metafurca serves for the attachment of the thoraco-
abdominal muscles. The pleural region of the metathorax is
a u arrow triangular space situated behind the lateral portion
of the metasternum and the posterior coxas. It is composed
of a narrow triangular episternum and epimeron. The former
(eps/")is bounded in front by the metasternum, the posterior
thoracic spiracle and the base of the haltere, below by the
posterior coxal foramen, and behind by the epimeron. The
epimeron (ep.") is also bounded below by the coxal foramen and
behind by the narrow dorsal arch of the metathorax and the
first abdominal segment, its apex comes in contact with the
base of the haltere. The dorsal region of the metathorax has
practically disappeared, all that can be recognised as rneta-
notum is a narrow chitinous strip (mil.) on each side between
the apex of the metapleural area and the dorsal edge of the
first abdominal area.
Wings. — The wings are situated at the sides of the
scutum on the alar membrane, to which are attached the
sclerites of the wing base. They are covered with very fine
hairs.
In describing the neuration of the wings the nomenclature
proposed by Comstock and Needham (1898) for the wings of
the whole group of insects will be employed.
The nervures of the wing are ocreacous. The anterior
edge of the wing (fig. 16) is formed by a stout nervure, the
costa (G'i.), which is very setose. The second longitudinal
nervure, the subcostal (#ci.), joins the costal about half way
along its length. A small transverse nervure, the humeral {h.)}
divides the costal cell into costal (G.) and first costal (1 C.) cells.
The next main nervure — the radial — divides into a number
of branches (in the typical insect five) ; some of these have
coalesced in the fly. A nervure joining the costal just past
the middle is the first radial (Bv) cutting off the subcostal
cell. The next nervure, which joins the costal on the apical
curve, represents the fused second and third radial nervures
(18)
412
C. GORDON HEWITT.
(B. 2+3). This cuts off the first radial cell (1 B.). The last
nervure, which joins the costal almost at the apex of the
wing, represents the fused fourth and fifth radial nervures
(B. 4 + 5), and so cuts off the third radial cell (SB.). The
fourth main longitudinal nervure is the median, which, in the
typical insect, divides into three, but in the fly the nervures
have undergone coalescence, as will be shown. The first and
second median nervures have coalesced (M. 1+2), and do
not run direct to the margin of the wing, but bend forwards
and almost meet B. 4 + 5 on the costa. About half way across
the wing a transverse nervure, the radio-medial (rm.) unites
B. 4 + 5 and M. 1 + 2, and cuts off the fifth radial cell (5 B.)
from the radial (/?.). The next longitudinal nervm'e repre-
sents the coalesced third medial and cubital nervures (31.
3 + Cu. 1). It runs to the posterior margin of the wing
about half way along the length of the latter. The nervures
31. 1+2 and M . 3 + Cu. 1 are united by two transverse
nervures. The proximal nervure — the medio-cubital (m.cic.)
cuts off the small triangular medial cell (31.) ; the distal trans-
verse nervure (m.) cuts off the first second medial cell (2 ill.1)
from the second second medial cell (2 H.2). The last longi-
tudinal nervure — the anal (Av) — is undivided, and does not
reach the margin of the wing, thus incompletely sepai'ating
the first cubital (1 Cu.) and anal (A.) cells. A small trans-
verse nervure, the cubito-anal (cu.a.), slightly more proximal
than the medio-cubital, cuts off the small triangular cubital
cell (Cu.) from the first cubital cell (1 Cu). Running parallel
with, and posterior to, the anal longitudinal nervure, there is
apparently another nervure. This, however, is not a true
nervure, but is merely a chitinised furrow giving additional
strength to the posterior angle of the wing. The posterior
edge of the base of the wing is divided into a number of
lobes. These are the anal lobe, and, as Sharp (1895) pro-
posed, the alula, antisquama, and squama. The squama is
thicker than the rest, and is attached posteriorly to the wing-
root between the mesoscutum and the lateral plates of the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 413
postscutelluin. It covers the haltere, as in all " calyptrate "
Muscida?.1
The Halteres. — The halteres or balances (fig. 6, hal.) are
generally considered to represent the rudimentary meta-
tboracic wings. They are covered by the squamaj, and are
situated on tbe sides of the thorax above the posterior
thoracic spiracles. Bach consists of a conical base on which
are a number of chordonotal sense-organs, and on this base
is mounted a slender rod, at the end of which a small spheri-
cal knob is attached. The wall of the distal half of this
sphere is thinner than the proximal half, and in preserved
specimens is generally indented. Experiments show that the
1 The nomenclature of Comstock and Needham lias not yet been adopted
by dipterologists in general ; but, on account of its great morphological value,
it will no doubt in course of time replace the present confused system. It
may therefore be useful if the nomenclature employed in the foregoing
description be compared with those most usually employed.
Longitudinal nervures. — Cv Costal. Scv Mediastinal, auxiliary. Rx.
Subcostal, 1st longitudinal. R. 2 + 3. Radial, 2nd longitudinal. R. & -f- 5.
Cubital, 3rd longitudinal ; ulnar (Lownc). M. 1 + 2. Median, 4fh longitu-
dinal; discal (Verrall). M. . 3 + Cuv Submedian, 5th longitudinal; postical
(Verrall). Av Anal, 6th longitudinal. Pseudonervure, axillary, 7th longi-
tudinal.
Transverse nervures. — h. Humeral, 1st transverse; basal cross vein
(Verrall). rm. Discal, 2nd transverse; middle cross vein (Verrall); medial
transverse; anterior transverse (Austen), vi-cu. Anterior basa! transverse
(Austen); lower cross vein (Verrall) ; postical transverse (Lowne). m. Pos-
terior transverse (Austen) ; postical cross vein (Verrall) ; discal transverse
(Lowne). cu-a. Posterior basal transverse (Austen) ; anal cross vein (Verrall);
anal transverse (Lowne).
Cells. — C. Costal. 1 C. Second costal. Sc. Third costal (Lowne cor-
rectly calls this " sub-costal"). 1R. Marginal. 'SR. Sub-marginal; cubital
(Lowne). 5R. Pirst posterior cell (Austen) ; sub-apical (Lowne and Verrall).
2. 1/5. Second posterior cell (Austen); apical. 1 Cu. Third posterior cell
(Austen and Verrall) ; patagial (Lowne). 2 Ml. Discal (this term is used also
in Lepidoptcra, Trichoptera, and Psocoptera, and in each family refers to a
different cell !). R. Anterior basal cell (Austen) ; upper or 1st basal or
radical (Verrall) ; prepatagial (Lowne). M. Posterior basal cell (Austen) ;
middle or 2nd basal or radical (Verrall); anterior basal (Lowne). Cu. Anal
cell (Austen) ; lower or 3rd basal or radical (Verrall) ; posterior basal (Lowne).
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414
C. G011D0N HEWITT.
hal teres are organs of a static function. They are not
balancing organs in the sense that they are equivalent to the
balancing pole of a rope-walker. They also have probably an
auditory function. They are innervated by the largest pair
of nerves in the thorax.
The Legs. — The three pairs of legs are composed of the
typical number of segments. Each consists of coxa, trochanter,
femur, tibia, and tarsus. The coxae are the only segments
which show any considerable difference in the three pairs of
legs. The anterior coxae are comparatively large and boat
shaped, the intermediate coxae are smaller and their separate
sclerites more marked ; the coxal plates of the intermediate
coxse are shown in fig. 6 (cp.). The coxal joints of the pos-
terior pair of legs are almost similar to those of the intei'-
mediate pair. The anterior femora are shorter and stouter in
the middle than those of the intermediate posterior pairs of
legs. The anterior tibiae are also shorter than those of the
succeeding legs. The anterior tibiae are covered on their
inner sides with closely-set, orange-coloured setae which serve
as a comb by meaus of which the fly removes particles of dirt
adhering to the setae which clothe its body ; the first tarsal
joints of the posterior legs are also similarly provided. The
tarsi consist of five joints, the terminal joints bearing the
" feet." These organs about which so much has been written
consist of a pair of curved lateral claws or " ungues " which
subtend a pair of membranous pyriform pads — the pulvilli.
The pulvilli are covered on their ventral sides with innumer-
able, closely-set, secreting hairs by means of which the fly is
able to walk in any position on highly polished surfaces. A
small sclerite lies between the bases of the pulvilli. The
tarsal joints and the other segments of the legs are covered
with a large number of setae.
3. The Abdomen.
The abdomen is oviform with the broad end basal. The
total number of segments which compose the abdomen is eight
in the male and nine in the female. The visible portion con.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 415
sists of apparently four segments in the male and female, in
reality there are five as the fh'st segment has become very
much reduced, and has fused with the second abdominal seg-
ment forming the anterior face of the base of the abdomen
(see fig. 8). The segments succeeding the fifth are greatly
reduced in the male, and in the female they form the tubular
ovipositor which, in repose, is telescoped within the abdomen.
The second, third, fourth, and fifth abdomiual segments are
well developed, and consist of a large tergal plate, which
extends laterally to the ventral side. The sternal plates are
much reduced, and form a series of narrow plates lying on
the ventral membrane along the mid-ventral line. The
spiracles are situated on the lateral margins of the tergal
plates. The sclerites of the abdomen which are exposed are
strongly setose, especially the fourth and fifth dorsal plates,
but they do not bear rnacrochasbse.
IV. Internal Structure.
1. The Muscular System.
The muscular system of the fly is similar to that of
Volucella, described by Kunckel d'Herculais (1881), and of
the Blow-fly, described by Lowne and Hammond, and conse-
quently they will be but briefly described. The muscles may
be divided into the following groups : 1. Cephalic, 2. Thoracic,
3. Segmental, 4. Those controlling the thoracic appendages,
and 5. Special muscles.
1. The cephalic muscles will be considered in the detailed
description of the head.
2. The thoracic muscles are enormously developed and
almost fill the thoracic cavity. They are arranged in two
series. The dorsales (figs. 13 and 15, do.) are six pairs of
muscle-bands on each side the median line, attached posteriorly
to the postscutellum and mesopbragma, and anteriorly to
the prescutum and anterior region of the scutum. The
sternodorsales (st.do.) are vertical and external to the dorsales
and are arranged in three bundles on each side. The first
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416
C. GORDON HEWITT.
two pairs have their upper ends attached to the prescutum
and scutum, and their lower ends inserted on the mesosternum,
the third pair is attached dorsally to the scutum and ventrally
to the lateral plate of the postscutellum above the spiracle.
As Hammond has shown in the blowfly (1881) all these
muscles are mesothoracic. The dorsales by contraction
loosen the alar membrane and so depress the wiug, the
sternodorsales have the opposite effect.
3. The segmental muscles. These muscles, which are so
prominent in the larva, have almost disappeared in the imago.
They are represented by the cervical muscles, certain small
thoracic muscles, the thoraco-abdominal muscles, and the
segmentally-arranged abdominal muscles together with the
muscles controlling the ovipositor and male gonapophyses.
4. The muscles controlling the thoracic appendages, the
wings, legs, and halteres. There is an elaborate series of
muscles controlling the roots of the wing, but in order to
avoid too much detail they will not be described here. The
flexor muscles of the anterior coxaa have their origin on the
inner surfaces of the humeri, a fact supporting the pro-
thoracic nature of these sclerites ; the flexors of the middle
pair of legs have their origin on the sides of the posterior
region of the prescutum. The internal muscles of the leg are
similar to those of the blowfly and Volucella.
5. Special muscles. These are the muscles controlling the
spiracular valves, the penis, and other small muscles.
2. The Nervous System.
The central nervous system (fig. 11) consists of (1) the
brain or snpracesophageal ganglia which are closely united
with the subcesophageal ganglia, the whole forming a compact
mass which I propose to call the cephalic ganglion (fig. 1,
C.G.), perforated by a small foramen for the passage of the
narrow oesophagus, and (2) the thoracic compound ganglion
which is composed of the fused thoracic ganglia with the
abdominal ganglia. The two compound nerve-centres are
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 417
united by a single median ventral cord running from the
subcesophageal ganglia to the anterior end of the thoracic
nerve-centre.
The cephalic ganglion consists of the supraoesophageal
ganglion and the subcesophageal ganglia so closely united
that the commissural character of the circumcesophageal con-
nectives is quite lost. Externally, on the dorsal side of the
brain three longitudinal fissures can be seen, a median fissure
and two lateral fissures marking the origin of the optic lobes.
The supraoesophageal ganglia. The characters of the ganglia
composing the brain are hidden by the sheath of cortical
cells which fills up the spaces between the ganglia, the
characters of these can be ascertained by the serial sections.
The median mass the procerebrum is formed by the fusion of
the procerebral lobes. These are united before and behind,
and enclose a central ganglionic mass — the central bodj^.
Behind the procerebrum two pairs of fungiform bodies arise.
On the anterior face of the procerebrum the antenual or olfac-
tory lobes which represent the deutocerebrnm are situated
laterally. Bach sends a nerve (figs. 1 and 11, an.n.) to the an-
tenna. Above these and on the dorsal side are a pair of lobes
— the frontal lobes contiguous with each other in the median
line — these belong morphologically to the tritocerebrum.
Posterior to these in the median dorsal line of the cerebrum
a single median nerve, the ocellar nerve (figs. 1 and 11,
oc.n.), arises ; this runs vertically to the ocelli. A pair of
lobes which correspond to Lowne's thalami of the blowfly are
situated external to and between the frontal and antennal
lobes. The peduncles of the optic lobes have their origins
from the sides of the procerebrum. Each optic peduncle (fig.
11, O.P.) contains three ganglionic masses which Hickson
(1885) has termed from the brain peripherally the opticon,
epiopticon, and periopticon (fig. 1, P.O.) respectively.
The subcesophageal ganglia (fig. 1, S.O.). The commissures
uniting the supraoesophageal ganglia to the oesophageal
mass cannot be recognised as such, owing to the extreme
state of cephalisation of the cephalic ganglia. They are
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418
0. GORDON HEWITT.
represented by the regions lateral to the oesophageal foramen,
and from the anterior side of each of them arises a pharyn-
geal nerve (figs. 1 and 11, ph.n.). From the ventral side of
the subcesophageal ganglia a pair of nerves — the labial nerves
(fig. 1, Ib.n.) — arise and run down the proboscis, innervating
the muscles of that organ ; on reaching the oral lobes they
bifurcate and branch freely, supplying the numerous sense
organs in those structures. The cortical cells (Leydig's
" Punktsubstanz "), which fill up the spaces between the
ganglia and form an investing sheath round the whole gang-
lionic mass, are of two kinds. The smaller cells are rounded,
their nuclei are large in proportion to the protoplasm, and
their protoplasmic fibres anastomose with each other. Among
these smaller cortical cells, and also occasionally in the
ganglionic substance, larger ganglionic cells occur, their
protoplasm taking the stain very readily. Unipolar, bipolar,
and tripolar ganglion cells are found.
The eyes. Each eye contains about 4000 facets. They
are similar in all respects to the eyes of the blowfly, which
have been fully described by Hickson (loc. cit.), whose
results my study confirms ; consequently, a description of
their structure will not be given. It should be noted that, in
spite of the fact that Hickson corrected many mistaken views
held by Lowne in his memoir (1884), these are repeated in
his monograph of the Blowfly.
The cephalo-thoracic nerve cord (fig. 11, c.n.) unites the
cephalic and thoracic ganglia. Near its junction with the
thoi-acic ganglion a pair of cervical nerves (cer.n.) arise,
innervating the muscles of the neck.
The thoracic ganglion (figs. 12 and 14) is pyriform, with
the broad end anterior, and rests on the entothoracic skele-
ton of the mesothorax. As in the cephalic ganglion, the
component ganglia are ensheathed in a cortical layer, which
is of the same nature. The nerves of the three pairs of legs
(pr.cr., ms.cr., mt.cr.) arise from three large ganglia, which
are the prothoracic (Pr.G.), mesothoracic (Ms.G.), and meta-
thoracic {Mt.O.) ganglia. These are united by a median
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 419
longitudinal band of nerve tissue, which runs dorsal to them,
and behind the metathoracic ganglia swells out into a gang-
lionic mass (J.. 6r.), which represents the abdominal ganglia.
In this median dorsal band there is a median dorsal fissure
stretching posteriorly from above the middle of the meso-
thoracic ganglia. The dorsal regions of the mesothoracic
and metathoracic ganglia show ganglionic swellings. From
the antero-dorsal sides of the prothoracic ganglia a pair of
prothoracic dorsal nerves (pr.d.) arise and supply the muscles
of that region, including those of the anterior thoracic
spiracle. The nerves supplying the mesothoracic legs
(ms.cr.) arise from the postero-ventral sides of the meso-
thoracic ganglia. Between the mesothoracic ganglia there
is. a median ganglionic mass, situated slightly dorsal, from
the middle region of which the nerve-fibres of the large pair
of dorsal mesothoracic nerves [m.s.d.) arise ; Lowne, in the
blowfly, calls these prothoracic. The roots of these nerves
are broad dorsoventrally. These nerves innervate the
sterno-dorsales muscles of the middle region. In this
median mesothoracic nerve centre, posterior to the origin of
the dorsal mesothoracic nerves, the fibres of a pair of nerves,
the accessory dorsal mesothoracic nerves (ac.ms.), have their
origin ; these appear externally to arise dorsal to the roots of
the mesothoracic crural nerves. The dorsal metathoracic
nerves (mt.d.), which innervate the halteres, and are the
largest pair of thoracic nerves, have their origin from the
median dorsal band in front of the metathoracic ganglia, so
that they appear to be almost mesothoracic in origin. The
metathoracic crural nerves (mt.cr.) arise from the posterior-
ventral sides of the metathoracic ganglia. Posterior to these
a pair of slender nerves, the accessory dorsal metathoracic
nerves, have their origin, and innervate the muscles at the
posterior end of the thorax.
The dorsal band becomes much thinner posterior to the
abdominal ganglion, and runs into the abdomen as a median
abdominal nerve (ab.n.). In the thorax two pairs of abdo-
minal nerves arise. In the abdomen the abdominal nerves
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420
0. GORDON HEWITT.
arise alternately and irregularly from the median abdominal
nerve. The median abdominal nerve finally terminates in
the genitalia.
3. The Alimentary System.
The alimentary canal of the house-fly is shorter than that
of the blowfly, and also than that of Glossina described by
Minchin (1905), and slightly longer than the alimentary tract
of St omoxys described by Tulloch (1906). It serves as a
good example of the Muscid digestive canal. It is of a
suctorial character, and consists of pharynx, oesophagus,
crop, proventriculus, ventriculus or chyle stomach, proximal
and distal intestine and rectum.
The pharynx has already been described, and will be
further referred to in the detailed description of the head.
At the proximal end of the fulcrum, where the oesophagus
arises, there is usually a small mass of cells, which Kraepelin
has described as glandular, but which I believe to be simply
fat-cells.
The oesophagus (figs. 1, 17, 20, ces.) commences at the
proximal end of the pharynx, and describes a curve before
passing through the oesophageal foramen in the cephalic
ganglion, where it narrows slightly. It then passes through
the cervical region into the thorax in the anterior region, of
which it opens into the proventriculus (figs. 17, 20, Pv.),
continuous with, and in the same line as the oesophagus, the
duct leading to the crop (fig. 20, d.cr.) passes along the
thorax dorsal to the thoracic nerve-centre, and entering
the abdomen it leads into the crop, which lies on the ventral
side of the abdomen. The oesophagus has a muscular wall,
enclosing a layer of flat epithelial cells, and is lined by a
cuticular intima, which is thrown into several folds at the
anterior end.
The crop (fig. 17, Cr.) is a large bilobed sac, capable of
considerable distension, and, when filled with the liquid food,
it loses its bilobed shape, and occupies a large portion of the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 421
antero-ventral region of the abdomen. Its walls exhibit
muscular (unstriped) fibres; the flat epithelial cells have a
very thin cuticle.
The pro ventriculus (Pv.) is circular and flattened dorso-
ventrally. Its structure will be understood by reference to
fig. 20. In the middle of the ventral side it opens into the
oesophagus, and on the dorsal side the outer wall is continued
as the wall of the ventriculus (Ven.). The interior is almost
filled up by a thick circular plug (Pv.p.), the cells of which
have a fibrillar structure, and it is pierced through the
centre by the oesophagus. The neck of the plug is sur-
rounded by a l'ing of elongate cells, external to which the
wall of the proventriculus begins, and, enclosing the plug at
the sides and above, it merges into the wall of the ventriculus.
I do not agree with Lowne in regarding the proventriculus
as "a gizzard and nothing more/' but its structure suggests
a pumping function and also that of a valve. On the dorsal
side of the oesophagus, at its junction with the proventriculus,
a small ganglion, the proventricular ganglion (Pv.g.), lies,
communicating by a fine nerve with the cephalic ganglion.
The ventriculus, or chyle stomach (figs. 17, 20, Ven.),
represents the anterior region of the mesenteron, the posterior
region of the latter being formed by the proximal intestine.
It is narrow in front, and widest in the posterior region of
the thorax, where it again narrows in passing through the
thoraco-abdominal foramen into the abdomen to become the
proximal intestine. Except in the anterior and posterior
regions, where columnar cells compose the digestive epi-
thelium, the walls of the ventriculus are thrown into a
number of transverse folds, which ai*e again subdivided
longitudinally, the result being the formation of small crypts
or sacculi, which are lined by large cells. These sacculi
correspond to the digestive cceca of other insects.
The proximal intestine (figs. 17, 21, p.int.) is the
longest region of the gut. It varies in length considerably.
In the normal-sized condition its course is as follows : —
Beginning at the anterior end of the abdomen it runs dor-
VOL. 51, PART 3. NEW SERIES. 32
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422
0. GORDON HEWITT.
sally beneath the heart to the posterior region, where it
curves downwards, turns to the left, and runs forward for a
short distance, curving to the right, where it doubles back
transversely to the left. Here it doubles sharply back to the
right, from whence it runs forward for a little way, and
crosses over to the left. Carving, it runs posteriorly to
become the distal intestine. Its walls are lined by an
epithelium of large columnar cells.
The distal intestine (d.inb.). The junction of this
with the proximal intestine is marked by the entrance of the
ducts of the malphigian tubes. It runs posteriorly, and
curves dorsally and forwards to become the rectum, from
which it is separated by a cone-shaped valve — the rectal
valve, the position of which is marked externally (fig. 21, X.).
The epithelium of the distal intestine consists of small
cubical cells, which project into the lumen, and are covered
by a fairly thick chitinous intima. The epithelial wall of
the distal intestine is thrown into usually about six longi-
tudinal folds.
The rectum (red.) is composed of three parts, an anterior
region, an intermediate region which is swollen to form the
rectal cavity, and a shorter region posterior to this which
opens externally by the anus. The anterior region is lined
by cubical cells, whose internal faces project into the lumen
of the rectum, and give the chitinous intima a tuberculated
structure. The intermediate region which forms the rectal
cavity contains the four rectal glands (rect.gl.). Its walls are
lined by a thin cuticle supported by a flattened epithelium.
The posterior portion of the rectum is short, and has thick
muscular walls. The cuticular intima is continuous with that
of the external skeleton.
Salivary Glands. — There are two sets of salivary glands
— a pair of labial and a pair of lingual glands. The structure
of the labial glands will be described in the account of the
anatomy of the head.
The lingual glands (fig. 17, sl.g.), though considerably
longer than the total length of the body, are of the simplest
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 423
tubular type. They are of uniform width throughout their I
whole length, except the slightly swollen blind termination. '
These blind ends lie one on each side of the ventral and
posterior region of the abdomen, generally embedded in the I
fat-body. They take a sinuous course forwards through the I
abdomen into the thorax, where they run alongside the ven-
triculus. At the sides of the proventriculus they are thrown
into several folds, which appear to be quite constant in cha-
racter. They pass forwards at the sides of the oesophagus
and on entering the cervical region the ducts lose their
glandular character, and assume a spiral thickening ; before
leaving the cervical i*egion the two ducts unite below the
oesophagus, and the single median duct enters the head ven-
tral to the cephalothoracic nerve cord, and runs direct to the
pi-oximal end of the hypopharynx, at the end of which it
opens. A short distance before entering the hypopharynx
the salivary duct (fig. 1, sal.d.) is provided with a small
valve controlled by a pair of fine muscles (s.m.), which
serves to regulate the flow of the salivary secretion. The
glands are composed of glandular cells (fig. 22), which are
convex externally, and have a fibrillar appearance in section.
No vacuoles have been found in the cells.
The Malpighian Tubes. — A pair of malpighian tubes
(fig. 21, malp.) arises at the point of junction of the proximal
and distal intestines, that is, where the mesenteron joins the
proctodeum. Bach malpighian tube shortly divides at an
angle of 180° into two malpighian tubules. The malpighian
tubules are very long and convoluted, and intimately bound
up with the diffuse fat-body, so that it is a matter of consider-
able difficulty to dissect them out entire. They have a
moniliform appearance and are of uniform width throughout;
never more than two cells can be seen in section. They are
generally yellowish in colour. As in most insects they are
undoubtedly of an excretory nature, as the contents of the
cells and tubules show. Lowne's view that, in the blowfly,
they are of the nature of a hepato-pancreas is untenable
morphologically and physiologically.
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424
0. GORDON HEWITT.
The Rectal Glands. — The four rectal glands (rect.gl.)
are arranged in two pairs, two on each side of the rectal
cavity. Each rectal gland (fig. 25) has a conical or pyriform
apex with a swollen circular base. It is composed of a single
layer of large columnar cells (r.gl), the papilla being hollow,
with the cavity in communication with the general body
cavity. It is covered externally by a perforate chitinous
sheath (sh.), which is continuous with the intima of the rectum.
A number of tracheae (tr.) enter the cavity of each gland, and
fine tracheae may be seen penetrating the wall. The cavity
of the gland is filled with a loose tissue of branching cells.
As the gland is capable of pulsation there is no doubt a
constant interchange of blood between the cavity of the gland
and the body cavity (which is a haemoccel). By this means
waste pi-oducts may be extracted from the blood by the
large gland cells and excreted into the rectum through the
pores on the external sheath of the gland. The rich supply
of tracheae probably assists the cells in the process of excre-
tion, as we find the tracheae very numerous, and intimately
connected with the malpighian tubules.
4. The Respiratory System.
The respiratory or tracheal system is developed to a very
great extent in the fly and occupies more space than any
other anatomical structure. Only by dissection of the freshly-
killed insect can one obtain a true conception of its impor-
tance. It consists of tracheal sacs of varying size having
extremely thin walls and tracheae which may arise from the
sacs, or, in the case of the abdominal tracheae, independently
from the spiracles.
The Anterior Thoracic Spiracles (figs. 6 and 13, a.th.).
— Each is a large vertical opening behind the humeral sclerite
and above the anterior legs. It is surrounded by a chitinous
ring, the peritreme and the opening is guarded by a number
of dendritic processes which prevent the entrance of dust
and other foreign bodies. It leads into a shallow chamber or
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STRUCTURE, DEVELOPMENT, AND BIONOMJ CS OF HOUSE-FLY. 425
vestibule which communicates with the rest of the spiracular
system through a valvular aperture.
The anterior thoracic spiracles supply the whole of the
head, the anterior and median regions of the thorax, the
three pairs of legs, and by means of the abdominal air-sacs
a large part of the viscera.
Internal to the valve the tracheal system divides. The
tracheal sacs springing from the posterior sideare as follows :
Ventrally a rather narrow tracheal duct leads into a sac —
the anterior ventral thoracic sac (fig. 18, a.v.s.) situated at
the side of the thoracic ganglion which it supplies. Above
the origin of this another tracheal duct leads to a vertical sac
supplying the anterior sterno-dorsales muscles. Dorsally
the ducts of two sacs take their origin; the smaller and more
dorsal is a flat sac closely apposed to the anterior ends of the
dorsales muscles (do.) which it supplies ; the more ventral of
the two is one of the two most important branches of the
anterior thoracic spiracle (the other being the branch
supplying the head). In the thorax it takes the form of an
elongated sac lying below the dorsales muscles, and by side
of the alimentary canal. From the dorsal side of this the
longitudinal thoracic sac (l.tr.s.) a number of branches arise
which supply the lower dorsales muscles. It is constricted
about the middle of its length and anterior to the constric-
tion ; a branch is given off which supplies the ventral portion
of the median sterno-dorsales muscles. In the posterior
region of the thorax another ventral branch is given off from
which branches arise, one supplying the ventral portions of
the posterior sterno-dorsales muscles, the other opening into
the posterior ventral thoracic sac (p.v.s), which supplies the
intermediate and posterior legs. The longitudinal thoracic
sac then narrows, and passes through the thoraco-abdominal
opening into the abdomen. In the adomen it immediately
dilates to form one of the large abdominal air-sacs (a.b.s.).
The pair of abdominal air sacs in some cases occupy about
half the total space of the abdomen. When the fat-body is
not greatly developed they occupy almost the whole of the
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426
C. GORDON HEWITT.
basal portion of the abdomen. They give off internally a
large number of tracheae which ramify among the viscera and
provide a large portion of the contents of the abdomen with
air.
From the anterior side of the anterior thoracic spiracle a
flattened sac arises. On its ventral side this gives off a
branch which supplies the muscles of the neck and the ante-
rior leg. The sac then narrows into a rather thick-walled
cervical tracheal duct (c.tr.), which passes through the neck
alongside the cephalo-thoraeic nerve-cord and enters the head.
Tracheal Sacs of the Head. — The tracheal sacs of the
head occupy the greater portion of the head capsule. They
entirely fill up all the space which would otherwise be hasmo-
ccel. These tracheal sacs are supplied by the cervical
tracheal ducts which, on entering the head capsule, curve
dorsally behind the cephalic ganglion. Before curving up-
wai'ds each gives off a large ventral duct (fig. 4), which
spreads out beneath the cephalic ganglion forming a structure
of a tentorial nature upon which the ganglion rests. The
dorsal cephalic ducts unite behind the cephalic ganglion
above the oesophagus. From the point of junction three
ducts arise, two lateral ducts and a median dorsal duct. The
median dorsal duct (m.d.) opens into a large bilobed dorso-
cephalic sac lying on top of the ganglion, and occupy-
ing the dorsal region of the head capsule. It gives off
branching tracheal twigs supplying the antero-dorsal portion
of the optic ganglion (periopticon). Each of the lateral
ducts (fig. 4, l.d.) supplies the posterior cephalic sacs. It
first communicates with a sac (fig. 13, p.c.s.) lying behind
the dorsal portion of the optic gauglion to which it gives off
a large number of tracheal twigs. This sac opens into an
elongate vertical sac which occupies the ventro-posterior
region of the head capsule. The remaining tracheal sacs of
the head are supplied by the tentorial tracheal ducts (tr.d.),
which spread out beneath the cerebrum in a fan-shaped
manner, and are bilaterally distributed. Each half, in addi-
tion to giving off internally tracheal twigs to the optic
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STIiUOTUEJfl, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 427
eranerlia, communicates with two tracheal sacs. An internal
duct leads into a large spherical sac, the anterior cephalic
sac (a.c.s.) situated in the anterior region of the head dorsal
to the fulcrum. From the dorsal side of this sac a branch
is given off which supplies the antenna of its side ; the ven-
tral side is continued down the fulcrum as a narrow tracheal
sac. The lateral portion of the tentorial tracheal duct opens
into the ventro-lateral cephalic sac (-y.es.) situated posterior
to the optic ganglion. The lower end of this sac gradually
narrows as it enters the rostrum which it traverses, giving
off half-way along its length a trachea which supplies the
palp of that side. On reaching the haustellum it takes the
form of a trachea proper, having annular thickenings.
Shortly after entering the haustellum it gives off two branches
to the muscles of this region. The main trachea is continued
into the oral lobe of its side where it divides into anterior
and posterior branches, and these again divide into numerous
small tracheaa running to the edges of the oral lobes. Lowne,
in his description of the tracheal system of the blowfly,
describes and figures the tracheal supply of the proboscis as
being of the nature of tracheal sacs and capable of distension ;
he also describes a trefoil-shaped tracheal sac at the base of
the oral lobes giving off very regular branches, the dilation
of which causes the inflation and tension of the oral lobes.
The mechanism of the proboscis will be discussed later (p. (45)
439), but it may be noticed here that in M. domestica
there is no trace of a trefoil-shaped sac at the base of the
oral lobes, and that all the tracheal structures of this the
haustellum region are definite annular tracheae, and there-
fore incapable of distension.
The posterior thoracic spiracle (tigs. 6 and 15, p.th.)
is triangular in shape and guarded by dendritic processes.
It possesses a vestibule which leads into a distributing tracheal
sac. The tracheal sacs of this system (fig. 15) have not the
extended range of those supplied by the anterior thoracic
spiracle, but ai*e confined to the thorax, chiefly in the median
and posterior regions which are not aerated to any great
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428
C. GORDON H 12 WITT.
exteut by those of the other system. They supply chiefly
the large muscles of the thorax. Laterally a series of sacs
(l.th.s.) extends autero-dorsally in an oblique direction, ex-
ternal to the sterno-dorsales muscles to the humeral region.
From the first of these sacs a large number of tracheal twigs
arise and supply the muscles of the wing and the anterior
sterno-dorsales muscles. Ventral to this sac a large sac
(m.v.s.) penetrates internally between the anterior and median
sterno-dorsales muscles and supplies the lower dorsales
muscles. From the dorsal side of the distributing sac a
number of sacs arise, some oE which penetrate between the
sterno-dorsales muscles and supply the upper dorsales mus-
cles. A more posterior set supplies the posterior regions of
the dorsales muscles, ramifying between them in a very
extensive manner, some ultimately terminating in the tracheal
sacs beneath the scutum and the scutellar sac (sc.s.).
The abdominal spiracles differ in number in the two
sexes. In the male there are seven pairs of abdominal
spiracles; in the female I have only been able to find five
pairs. In both sexes each of the large tergal plates which
cover the abdomen has near its lateral margin a small circular
spiracle. The first abdominal segment which has fused with
the second has a pair of small spiracles (see fig. 8) slightly
anterior to those of the second (apparent first) abdominal
segment. In addition to these the male possesses two pairs
of spiracles in the membrane at the lateral extremities of the
rudimentary sixth and seventh abdominal segments (see
fig. 5). In the female I have been unable to find any addi-
tional spiracles. Each of the abdominal spiracles is provided
with a vestibule and atrium which are separated by a valve
controlled by a minute chitinous lever. All the spiracles
of the abdomen communicate with trachea? which ramify
among the viscera and fat-body ; there are no tracheal sacs
in connection wilh these spiracles.
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STltUUTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 429
5. The Vascular System and Body-cavity.
By the great development of the tracheal sacs in the head,
the muscles in the thorax, and the fat-body and air sacs in
the abdomen, the hasnioccelic space in the fly is greatly
reduced. The blood is colourless, and is crowded with cor-
puscles, mostly containing substances of a fatty nature.
The fat-body varies greatly in the extent of its develop-
ment. In some cases it may almost fill the body-cavity,
pushing the intestine back into a postero-dorsal position :
this is generally the case in flies before hibernating; in other
cases it may be only moderately developed. The fat-body
receives a very rich tracheal supply, and stores the products
of digestion which are conveyed to it by the blood with which
it is bathed. It consists chiefly of very large cells, both
uninucleate and multinucleate ; the fat-cells of the head are
not so large.
The dorsal vessel or heart lies in the pericardial chamber,
immediately beneath the dorsal surface. It extends from the
posterior end to the anterior end of the abdomen, and four
large chambers, corresponding to the four visible segments,
and a small anterior chamber can be recognised ; the last
represents the chamber of the first abdominal segment. The
chambers are not separated by septa, but each has a pair of
dorso-lateral ostia situated at its posterior end where the alar
muscles of the pericardium arise. The walls of the heart are
composed of large cells. The pericardium contains fat-cells
and trachea;, and its floor is composed of large cells of a
special nature. The alar muscles run laterally in the floor of
the pericardium to the sides of the dorsal plates where they
are inserted. The anterior end of the heart is continued as a
narrow tube (fig. 20, d.a.) along the dorsal side of the ven-
triculus, where it terminates in a mass of cells (l.g.), which
are usually considered to be of a lymphatic nature.
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430
C. GORDON II li WITT.
6. The Eeproductive System.
The two sexes are slightly different in size, the females
being larger than the males; the sexual dimorphism of the
width of the frontal region of the head has already been
noticed (p. (8) 402). There does not appear to be any great
disparity in the numerical proportions of the sexes; near
breeding places there is naturally a preponderance of
females.
The Female Reproductive Organs. — The generative
organs of the female consist of ovaries, spermathecaa or
vesiculas seminales, accessory glands and their ducts.
The ovaries, when containing mature ova, occupy the
greater part of the abdominal cavity (fig. 23, ov.). They lie
ventral to the gut, occupying the whole of the ventral and
lateral regions, the gut resting on the V-shaped hollow
between them. Each ovary contains about seventy ovarioles,
in each of which ova in various stages of development can be
seen. The two short thin-walled oviducts (ov.d.) unite on
the ventral side of the abdomen to form the common oviduct
(c.o.d.). The walls of the common oviduct are muscular, and
when the ovipositor is in a state of rest, retracted into the
abdominal cavity, the oviduct curves forwards and dorsally
to enter the ovipositor (ov.p.) ventral to the rectum (rect.).
Here it swells slightly to form a sacculus (fig. 26, sac.) which
leads into the muscular vagina (vag.). The vagina opens into
the ventral side of the ovipositor immediately behind the
sub-anal plate.
The spermathecas (sp.) or vesiculaa seminales are three in
number, two on the left side, and a single one on the right.
Each consists of a small, black, oviform, chitinous capsule, the
lower half of which is surrounded by a follicular investment
continuous with the cellular wall of the duct, the whole hav-
ing the appearance of an acorn with a long stalk. The ducts
of the spermatheca? are lined by a thin chitinous intima con-
tinuous with the chitinous capsule, and they open at the pos-
terior end of the sacculus on the dorsal side.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 431
There is a single pair of accessory glands (ac.g.), which are
fairly long, and on n earing the vagina they become narrower
to form a slender duct, which opens on the dorsal side of the
vagina immediately behind the ducts of the sperrnathecse.
The accessory glands are closely united with the fat-body.
They probably secrete the adhesive fluid which covers the
eggs when they are laid, and causes them to adhere to each
other and to the material upon which they are deposited.
Behind the accessory glands there is a pair of thin-walled
transparent vesicles (tasche dell5 o vid utto of Berlese),
which I propose to name the accessory copulatory vesicles
(a.cu.)'on account of the par-t they take in ensuring firm
coitus with the male during copulation, during which process
they expand to a much, greater extent.
The ovipositor (fig. 8). The terminal abdominal segments
of the female are much reduced to form a tubular ovipositor,
the chitinous sclerites being reduced to form slender chitinous
rods. When extended it equals the abdomen in length. It
is composed of segments vi, vii, viii, and ix, each being sepa-
rated from the adjacent segments by an extensible inter-
segmental membrane, which is covered with fine spines.
When the ovipositor is retracted (fig. 23, ovp.) it lies in the
interior of the posterior end of the abdomen, the segments
being telescoped the one within the other, so that only the
terminal tubercles are visible from the exterior. The dorsal
arch of the sixth abdominal segment is reduced to a A-shaped
sclerite (vi, d.), lying on the dorsal side of the segment.
The ventral arch of this segment is reduced to a slender
chitinous rod (vi, v.) in the mid-ventral line. The dorsal
arch of the seventh segment is represented by two slightly-
curved sclerites (vii, cZ.), with their concave faces opposite;
the ventral arch (vii, v.) is similar to that of the sixth
segment. At the junction of the posterior ends of the
sixth and seventh segments with the inter-segmental mem-
branes succeeding them there are several setose tubercles
arranged more or less in pairs, but they vary in development
in different individuals. The dorsal arch of the eighth
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432
C. GORDON HEWITT.
segment consists of two parallel and slender sclerites (viii, d.),
not so narrow as those of the two preceding segments. A
pair of slender sclerites (viii, v.) also represents the ventral
arch. The terminal anal segment, which I consider repre-
sents the reduced ninth segment, has a dorsal chitinous
sclerite, the sub-anal plate (su.p.), which is triangular in
shape, and a ventral sub-aual plate of the same shape. The
female genital aperture is situated at the anterior end of the
latter plate, between the eighth and anal (ninth) segments.
A pair of terminal setose tubercles is situated laterally at the
apex ot' the anal segment.
The Male Reproductive Organs. — The male repro-
ductive organs (fig. 24) are situated ventral to the alimentary
canal, and lie within the fifth abdominal segment. They
consist of a pair of testes, vasa deferentia, ejaculatory duct
and sac, and the termiual penis. There are no accessory
genital glands in the male.
The testes (te.) are a pair of brown pyriform bodies, with
their long axes placed transversely, and their pointed ends
facing. In young males they have a bright red appearance.
They are covered with a follicular investment of cells, which
varies in thickness apparently according to age. The thin
brown chitinous capsules contain the developing spermato-
zoa. The pointed end of each testis is continued as a fine
vas deferens (v.d.), which meets that of the other testis in the
median line, where they open into the common ejaculatory
duct (d.e.). This runs forwards for a short distance, and then
bends to the left ventrally, and, after several convolutions on
the left ventral side of the abdomen, the duct narrows con-
siderably, forming a narrow ejaculatory duct. This crosses
over the dorsal side of the rectum to the right side, where it
runs forwards for a short distance and then curves back in
the median ventral line, opening into a pyriform ejaculatory
sac (e.s.). The walls of this ejaculatory sac are muscular,
longitudinal muscles, giving the walls a striated appearance.
It contains a phylliform, chitinous sclerite — the ejaculatory
apodeme (e.a.), which has a short handle at the broad end.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 433
This sclerite is, no doubt, of great assistance in propelling
the seminal fluid along the ejaculatory duct during copula-
tion. A short distance behind the ejaculatory sac the duct
opens into the peuis.
The Male G-onapophyses. — The extremity of the
abdomen in the male (fig. 10) has undergone considerable
modification in the formation of the external genitalia. The
visible portion of the abdomen, as seen from above, consists
of the first five abdominal segments; the remaining three
segments are slightly withdrawn into the fifth segment, and,
on looking at the abdomen from the posterior end, only the
terminal segment, the eighth, surrounding the anus, can be
seen. The sixth and seventh segments have been greatly
reduced. The sternal portion of the fifth segment consists
of a cordiform sclerite (V.v.), the apex of which is directed
forwards, and each of the lateral margins of the base is
produced to form a short process, swollen at the tip — these
lateral processes form the primary forceps (p./.)> and lie at
each side of the aperture of the male genital atrium (g.a.), of
which the posterior edge of the sclerite forms the lower or
anterior lip. The dorsal plates of the sixth and seventh
segments lie on the membrane, which is tucked underneath
the posterior edge of the fourth abdominal segment. The
dorsal plate of the sixth segment (vi, d.) is a narrow, trans-
verse sclerite ; its lateral edges, which do not extend down
the sides, are slightly produced anteriorly. The ventral
plate of the sixth segment (vi, v.) is asymmetrical, and, with
the dorsal plate of the seventh segment, produces a pro-
nounced asymmetry of the posterior end of the male abdo-
men. It consists of a spatulate plate on the left side, the
anterior or ventral side of which is produced into a narrow
bar extending across the ventral side of the aperture of the
genital atrium, its distal extremity bifurcating. The dorsal
plate of the seventh segment (vii, d.) is asymmetrical. It
consists of a narrow sclerite, which, on the dorsal side, is
similar to the sixth dorsal plate, but the left side (see fig. 5)
extends down the side, and broadens out into a somewhat
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434
0. GORDON HEWITT.
triangular-shaped area ; the anterior edge of this is incised,
and receives the seventh spiracle (vii, a.sp.) ; the ventral
edge is internal to the spatulate portion of the sixth ventral
plate. The ventral arch of the seventh sclerite has been
completely withdrawn into the abdomen, and consists of
a pair of curved sclerites (fig. 9, vii, v.), somewhat rhom-
boidal in shape, lying dorsal to the fifth ventral arch and
ventral to the penis (P.); they form the secondary forceps.
Their lateral edges, which are thickened articulate with the
alar processes of the body of the penis (c.pe.), and with the
dorsal arch of the eighth abdominal segment (viii, d.). Their
inner edges are curved, and almost meet in the mid-ventral
line. The dorsal arch of the eighth and last abdominal
segment (viii, d.) forms the apes of the abdomen. It consists
of a strongly convex sclerite, deeply incised on the ventral
side; in this incision the vertical slit-like anus (fig. 10, an.)
lies. The ventral portion of the segment is completed by a
pair of convex sclerites (viii, v.), which are united in the mid-
ventral line, forming the ventral border of the anal membrane
and the dorsal side of the entrance to the genital atrium.
All the sclerites of the posterior segments except the sixth
and seventh are setose.
Berlese (1902) in his account of the copulation of the
House-fly describes the genitalia. From his account of the
male genitalia he appears to have missed the narrow dorsal
arch of the sixth segment, or, what is very probable, he may
have mistaken it for the fifth dorsal arch, as he terms the
seventh dorsal arch the sixth, and describes what I have
called the ventral arch of the seventh as the dorsal arch of
that segment. This mistake in nomenclature has probably
arisen from the fact that he considered the visible portion of
the abdomen as consisting of four segments instead of five,
in which case the narrow dorsal arch of the sixth segment
would naturally be taken for that of the fifth.1
1 Berlese describes a sinistral asymmetry of the posterior segments, but
his figures show a dextral asymmetry, a mistake probably in the reproduction
of his figures which has escaped the author's notice.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 435
The penis (fig's. 7 and 9) lies internally on the ventral side
of the abdomen, dorsal to the ventral arches of the fifth and
seventh segments. It is composed of several sclerites. A
median sclerite (cpe.), the anterior and ventral edge of which
is roughly semicircular in outline, forms the body of the
penis. This is produced laterally to form two alar processes ;
at the bases of these processes the lateral extremities of the
dorsal arch of the eighth segment articulate with the body of
the penis; the extremities of the processes are attached to
the lateral extremities of the ventral sclerites of the seventh
segment, the secondary forceps. The penis proper consists
of a hollow cylindrical tube, the theca, which receives the
ejaculatory duct. The theca articulates with the body of the
penis by means of a pair of small chitinous nodules (" cor-
netti" of Berlese) ; posterior to the attachment the theca is
constricted slightly. Below the aperture for the entrance of
the ejaculator3r duct, the theca is produced into a ventrally
directed curved pi'ocess, the inferior apophysis (i.ap.) ; above
the aperture a short cylindrical process, the superior apo-
physis (s.ap.), arises. The anterior end of the theca is con-
tinued as a slightly inflated hyaline structure, the glans
(p.gl.), at the curved extremity of which the ejaculatory duct
opens.
V. The Internal Structure oe the Head.
The skeletal framework and tracheal system of the head
have already been described. It remaius, therefore, to give
an account of the musculature of the head and pharynx, and
also an account of the oral lobes.
- The posterior region of the head (tig. 1) not occupied by
tracheal sacs is usually filled up with small multinucleate fat-
cells {f.c), which are also occasionally found in the proboscis.
The frontal sac or ptilinium (Pt.) fills up the anterior portion
of the head not occupied by air-sacs. Its crescentic opening,
the lunule, has already been described. It is attached to the
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436
0. GOIiDON HEWITT.
wall of the cephalic capsule by muscles which vary consider-
ably in the extent of their development. In recently
emerged flies the muscle-supply of the ptilinium is consider-
able, as they have served to retract the sac after it has been
inflated to assist the exclusion of the imago, but in older
specimens it becomes less. The walls of the ptilinium are
muscular and lined by a chitinous intima covered with small
broad spines.
The Musculature of the Proboscis. — The chief
muscles controlling the movements of the pharynx and pro-
boscis are these :
The Dilators of the Pharynx (figs. 1 and 2, d.ph.) —
This pair of muscles occupies the interior of the fulcrum.
Each muscle is attached to the antero-lateral regions of the
fulcrum and inserted into the dorsal plate of the pharynx
(r.p.). These muscles are the chief agents in pumping the
liquid food into the oesophagus, and in drawing it up through
the pharyngeal tube.
The Retractors of the Fulcrum (fig. 1, r./.). — These
muscles are attached to the internal anterior edges of the
genae, and are inserted into the posterior cornua (p.c.) of the
fulcrum. Their contraction causes the rotation of the fulcrum
on the epistome as a hinge in the retraction of the proboscis.
The Retractors of the Haustellum (r.h.). — These
muscles have their origin on the dorso-lateral regions of the
occiput. They are long and narrow, and running on each
side of the common salivary duct are inserted into the dorsal
margin of the theca.
The Retractors of the Rostrum (r.r.). — This pair of
muscles has its origin at the sides of the occipital foramen,
and is inserted into the posterior side of the membranous
rostrum about half-way down its length. In the retraction
of the proboscis these muscles draw iu the rostrum.
The last two pairs of muscles acting together assist in the
retraction of the whole proboscis.
The Flexors of the Haustellum {f.h-) have then-
origin close to that of the retractors of the rostrum at the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 437
sides of the occipital foramen. They are inserted into the
base of the labral apodeme (ap.), and serve to flex the
haustellum on to the anterior face of the rostrum.
The Extensors of the Haustellum (ex.h.). — Each of
these muscles arises from the distal cornu of the fulcrum, and
is inserted into the head of the labral apodeme.
The Accessory Flexors of the Haustellum (a.f.h.)
are attached to the lower (distal) anterior margin of the ful-
crum, and inserted with the extensors into the head of: the
labral apodeme.
The Flexors of the Labium-epipharynx (f.l.). —
These muscles have their origin on the anterior and upper
edge of the fulcrum, and are inserted into the proximal end
of the labium-epipharynx. The first pair of the last three
sets of muscles serve to extend the haustellum in the exten-
sion of the proboscis, and the remaining two pairs assist in
the retraction of the proboscis by flexiug the haustellum on
to the rostrum.
A pair of very fine muscles (s.m.) have their origin at the
base of and internal to the posterior cornua of the fulcrum.
They are inserted into the dorsal side of a small valve (s.v.)
on the common salivary duct which regulates the flow of the
secretion of the lingual salivary glands.
The muscles of the haustellum are —
The Retractors of the Furca {r.fu.). — A pair of
muscles having their origin on the upper jjart of the theca.
Each is inserted along the upper proximal half of the lateral
process of the furca. When the muscles contract the lateral
processes of the furca, which, in a state of repose are brought
together by the elasticity of the ventral cornua of the theca,
are diverged, and thus cause the divergence and opening of
the oral lobes.
The Retractors of the Discal Sclerites (r.d.s.). —
These muscles have their origin on the lateral edges of the
upper part of the theca, and are inserted upon the sides of
the discal sclerites. They work together with the retractors
VOL. 51, PART 3. NEW SERIES. 33
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438
0. GORDON HEWITT.
of the furca, their contraction causing the divergence of the
discal sclerites, and the consequent opening of the oral pit.
The Dilators of the Labium-hypopharynx {di.L).
— These fan-shaped muscles arise in the middle region of
the theca on either side the median line, and diverging
are inserted in the lateral edges of the labium-hypopharyngeal
sclerite. By their contraction they will widen the channel of
the labium-hypopharynx.
The Dilators of the Labium-epiphary nx (di.L) —
These form a series of short muscles attached to the anterior
and posterior walls of the labium-epipharynx. The size of
the pharyngeal channel will be regulated by these muscles.
The Oral Lobes. — The external structure of the oral lobes
has already been described. Their internal structure and
histology will be given here, as it seemed preferable to do so
rather than postpone it to a future communication.
The setigerous cuticle and the p&eudo-tracheas lie on a
hypodermis of cubical cells (fig, 18, hy.). Beneath thehypo-
dermis of the aboral surface is another layer of cells contain-
ing a large amount of dark pigment. Each of the large
marginal sensory bristles (g.s.) of the aboral surface has a fine
channel running down the whole length of the seta. This
channel communicates with the cavity of a pyriform mass of
nerve-end cells {s.p.)} consisting of five or six cells. These
masses of cells occupy a large part of the interior of the oral
lobes. As these gustatory bristles are exposed and directed
ventrally when the proboscis is retracted, they may assist the
fly in testing the nature of its food before extending its pro-
boscis. On the oral side of the oral lobes the nipple-like gus-
tatory papillae (figs 1 and 18, gp.) have already been descrided.
The aperture at the end of the papilla leads into a fine duct,
which ends in a pyriform sensory bulb (s.g.p.). The tracheae
(tr.) can be seen running through the cells, some of which con-
tain several nuclei, and from their appearance are probably
derived from the fat-body. No tracheal sacs could be found
either in the oral lobes or at their bases, but the annular
tracheae are continuous with those of the proboscis. The
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY, 439
haBmoccel of the oral lobes is well developed. This supports
the view set forth by Kraepelin, and with which I agree that
the inflation of the oral lobes is due to the blood. I consider
that the extension of the proboscis is due to the inflation of
the tracheal sacs of the head. The proboscis having been pro-
truded the oral lobes are then diverged by the contraction of
the retractor muscles of the fnrca and discal sclerites, and dis-
tended by the inrush of blood which keeps them turgid, and
causes the openings into the pseudo-tracheal channels to
remain open.
The Labial Salivary Glands (figs. 19 and 1, Ib.sl.). —
These salivary glands lie in the haustellum at the base of the
oral lobes. The glands, which are spherical in shape, are com-
posed of a large number of gland cells somewhat triangular
in shape. Each gland cell is 40 fi in size, and possesses a
large nucleus (12 fx), and internal to this a permanent circular
vacuole (vac), which is 16 li in size, and is lined by a thin
chitinous intima. The duct of each gland cell opens into the
side of the vacuole (od.). The ducts (ic.d.) are intracellular,
and run from the centre of the gland, some of them uniting,
to form a number of fine ducts on the ventral sides of the discal
sclerites, which unite and open into the oral pits by a median
pair of pores. Kraepelin, in his description of the proboscis
of the blowfly, described the labial glands and their ducts
(but not their histology) of that insect, his description being
similar to the condition I find in M. domestica. Lowne,
however, states that in the blowfly he traced the ducts of the
gland cells through the oral lobes to the apertures of the
gustatory papillae, which he regarded therefore as the aper-
tures of the labial salivary glands.
The secretion of the labial salivary gland serves to keep
the surface of the oral lobes moist.
VI. Summary.
1. The exoskeleton of the head capsule and of the pharynx
is described in detail ; the relations of the parts in the terms
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440
0. GORDON HEWITT.
generally employed by dipterologists to the morphological
divisions of the insect head capsule are shown. On morpho-
logical grounds, the view that the distal portion of the
proboscis represents the modified second maxillas or labium
is adopted, as opposed to that of a first maxillar derivation
put forward by Lowne for the blowfly.
2. After a detailed description of the external and in-
ternal skeletal structures of the thorax, the neuration of the
wings is described in the terms proposed by Comstock and
Needh am in their valuable memoir ; and to facilitate their
more general adoption for the wings of the Muscidee and
other Diptera, a comparison is made between their nomen-
clature and the several systems employed in describing the
muscid wing.
3. The abdomen is shown to consist of eight segments in
the male and nine in the female, in both cases the first five
segments form the visible portion of the abdomen j the
external genitalia of the two sexes are described under
another section.
4. As the muscular system does not differ from that of
Volucella described by Kunckel d'Herculais and the blow-
fly described by Hammond and Lowne, it is briefly described.
The cephalic muscles, however, are fully described in the
detailed description of the head (V).
5. The nervous system, which is of the normal muscid type,
is described, but for the sake of clearness a very detailed
description of the composition of the cephalic ganglion is not
given. The structure of the optic tract is similar to that of
the blowfly as described by Hickson. The structure of the
thoracic nerve-centre is found to differ slightly from that of
the blowfly as described by Lowne.
6. The alimentary canal is similar in its structm-e to those
of Stomoxys and Grlossina, only differing in a few details.
The mesenteric region, which is represented by the ventri-
culus or chyle, stomach, and proximal intestine, is well
developed. The lingual salivary glands, rectal glands, and
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 441
Malpighian tubes are described ; the function of the rectal
glands is believed to be of an excretory nature.
7. As the tracheal systems of the Diptera have not received
much attention a detailed account of the tracheal system is
given. There are two thoracic spiracles, the first of which
supplies the whole of the head, the anterior and median
regions of the thorax and the three pairs of legs, and by
means of a pair of large abdominal air- sacs a large part of
the viscera. The posterior thoracic spiracle supplies the
muscles of the median and posterior region of the thorax,
especially the large dorsales muscles. There are seven pairs
of abdominal spiracles in the male and five pairs in the female
all of which are connected with trachea? only.
8. The dorsal vessel or heart is found to consist of five in-
complete chambers, each with a pair of ostia. The anterior
end is continued forwards along the dorsal side of the ventiu-
culus, and terminates in a glandular mass in the anterior
margin of the proventriculus.
9. The reproductive organs of the male are simple, con-
sisting of a pair of testes, vasa deferentia, and common
ejaculatory duct; there are no accessory glands such as are
found in many other Diptera. The terminal abdominal
segments of the male exhibit a sinistral asymmetry.
The ovaries of the female, when mature, occupy the
greater portion of the abdominal cavity. There are a pair
of accessory glands (probably of a "gum" or "glue"
nature), three spermatheceaa, and a pair of vesicles used
during copulation. The ovipositor is about as long as the
abdomen, and is composed of segments six to nine.
10. The musculature of the head is described in detail, and
it is found that the House-fly agrees with the blowfly in the
number and relations of its cephalic muscles, though in a few
cases the attachments are slightly different. In the haus-
telliim and oral lobes of the House-fly no tracheal sacs similar
to those described and figured by Lowne for the blowfly
occur, but only annulated tracheae are found, and, as these
are incapable of distension, the view that the oral lobes are
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442
0. GORDON HEWITT.
distended by the action of inflated air cannot be held. The
extension of the proboscis I believe is due to the inflation of
the tracheal sacs of the head and rostrum, and I agree with
Kraepelin that the distension of the oral lobes is effected by
blood-pressure.
Two kinds of gustatoi*y sense-organs are found on the
margin of the aboral and on the oral surfaces respectively.
The latter were described in the blowfly by Lowue as the
openings of the ducts of the labial salivary glands, but
Kraepelin's correct description of their structure in the
blowfly is confirmed by this study of the House-fly. The
labial salivary glands are described in detail. They consist
of large cells containing permanent vacuoles, which com-
municated with intracellular ducts. These open by a pair of
pores into the oral pits, the secretions of the glands serving
to keep the surface of the oral lobes moist.
VII. Literature.
The following is not intended to be a full list of the litera-
ture relating to M. domestic a. Further references will be
given in the succeeding parts.
1824. Andouin, V. — " Bicherches Analomiques sur le thorax des Animaux
Articules et celui des Insectes Hexapodes en particuliere," 'Atiu.
Sci. Nat. Zool.,' vol. i.
1906. Austen, E. E. — * Illustrations of British Blood-sucking Flies,' 74 pp.,
34 col. plates. Brit. Mus. (Nat. Hist.), Loudon.
1902. Berlese, A. — "L'accoppiamento della Mosca domestics," 'B,ev.
Patolog. vegetale,' vol. ix, pp. 345—357, 12 figs.
1834. Bouche, P. Fb,.— ' Naturgeschichte der Insekten,' Berlin.
1898.— Comstock, J. H., and Needham, J. G. — "The Wings of Insects,"
'Amer. Nat.,' vol. xxxii, p. 43, etc., and through the vol. into
vol. xxxiii.
1752-78. De Geek, Carl.—1 Memoires pour servir a l'Histoire des Insectes,'
Stockholm.
1881. Hammond, A. — "On the Thorax of the Blowfly (Musca vomi-
toria)," ' Journ. Linn. Soc' (Zool.), vol. xv, pp. 9—31, 2 pis.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 443
1854. Hepworth, J.—" On the Structure of the Foot of the Fly,"
'Q. J. M. S.,' vol. 2, pp. 158—160.
1885. Hickson, S. J.—" The Eye and Optic Tract of Insects," 'Q. J. M. S.,'
vol. 25, pp. 1—39, 3 pis.
1902. Howard, L. 0. — " House-flies " (in ' The Principal Household Insects
of the United States,' by L. 0. Howard and C. L. Marlatt), United
States of America Dept. of Agriculture, Washington. Division of
Entomology. Bull. No. 4, N.S., revised ed., pp. 43—47, and figs.;
aud (1898) Circular No. 35, 2nd series, pp. 1 — 8, and figs.
1890. Keller, J. C. — 'Geschichte der gemeinen Stubenfliege,' 32 pp.,
4 pis., Nurnberg.
1883. Kraepelin, K. — " Zur Anatomie und Physiologie des Russels von
Musca," 'Zeit. f. wiss. Zool.,' vol. xxxix, pp. 683—719, 2 pis.
1875-81. Kunckel d'Herculais, J. — 'Recherches sur l'organisation et le
Developpement des Volucelles,' Paris.
1758. Linneus, C. de. — 'Systema naturae' (10th ed.), vol i, p. 596; and
'Fauna suecica,' ed. ii, Holmia?, 1761.
1870. Lowne, B.T. — 'The Anatomy and Physiology of the Blowfly (Musca
vomitoria),' 121 pp., 10 pis., London.
1884. "On the Compound Vision and the Morphology of the Eye
in Insects," 'Trans. Linn. Soc' (Zool.), vol. ii, pt. 11.
1895. 'The Anatomy, Physiology, Morphology, and Development
of the Blowfly (Calliphora ery throcephala),' 2 vols., London.
1880. Macloskie, G.— "The Proboscis of the House-fly," 'Amer. Nat.,'
vol. v, pp. 153—161.
1897. Merlin, A. A. C. E.— " The Foot of the House-fly," ' Journ. Quekett
Club' (2), vol. vi, p. 348.
1905. " Supplementary Note on the Foot of the House-fly," 'Journ.
Quekett Club ' (2), vol. ix, pp. 167, 168.
1905. Mikchin, E. A.— "Report on the Anatomy of the Tsetse-fly (Glos-
sina morsitans)," 'Proc. Roy. Soc.' (Ser. B), vol. lxxvi, pp. 531
— 547, and figs.
1874. Packard. A. S. — "On the Transformations of the Common House-
fly, with Notes on allied forms," ' Proc. Boston Soc. Nat. Hist.,'
vol. xvi, pp. 136—150, 1 pi.
1738. Reaumur, R. A. F. de.— ' Memoires pour servir a l'Histoire des
Insectes,' Paris (vol. iv).
1860. Samuelson, J., and Hicks, J. B. — " The Earthworm and the Common
House-fly," 'Humble Creatures,' pt. i, 79 pp., 8 pis., London.
'The House-fly,' pp. 26—79, pis. 3—8.
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1 [ I
C. GORDON HEWITT.
18G2. Schiner, J. R. — ' Fauna Austriaca : die Fliegen.' 2 vols., Wien.
1895. Sharp, D.— " Insects," part ii, ' Cambridge Nat. History,' London.
1906. Tulloch, F. — "The Internal Anatomy of Stomoxys," 'Proc. Hoy.
Soc.' (Ser. B.), vol. lxxvii, pp. 523—531, 5 figs.
1906. Wesche, W.— "The Genitalia of both Sexes in the Dipl era, and
their relation to the Armature of the Mouth," 'Trans. Linn. Soc.,'
vol. ix, pp. 339—386, 8 pis.
The University,
Manchester.
EXPLANATION OF PLATES 22—26,
Illustrating Mr. 0. Gordon Hewitt's paper on " The Structure,
Development, and Bionomics of the House-fly (Musca
domestica, Linn.). Part I. Auatomy of the Ely."
PLATE 22.
Fig. 1. — Musea domestic a. Female.
Fig. 2. — Anthomyia radicum. Female.
Fig. 3. — Homalomyia canicularis. Male.
Fig. i. — Stomoxys calcitrans. Female. The halters of this species
have been drawn too far back, and in this and the other species the nervures
of the wings have been made thicker than they naturally are.
These figures are not drawn to the same scale.
PLATE 23.
Fig 1. — Interior of the head of M. domestica. In this figure the left
side of the head capsule and of the proboscis have been removed and the
compound eye of the same side, leaving the optic ganglion (periopticou). All
the tracheal structures have been omitted.
a.c. Anterior cornu of fulcrum, a.f.h. Accessory flexor muscles of hau-
stellum. ap. Apodeme of labrum. an.n. Antenual nerve. C.G. Cephalic
ganglion, di.l. Dilator muscles of labium hypopharynx. d.ph. Dilator
muscles of pharynx, d.s. Discal sclerite. ex.h. Extensor muscle of hau-
stellum. F. Fulcrum. /. Furca. f.c. Fat-cells, f.h. Flexor muscle of
haustellum. f.l. Flexor muscle of labrum-epipharynx. g.p. Gustatory
papilla; of oral lobes, k. Hyoid sclerite of pharynx. Ib.n. Labial nerve.
lb. si. Labial salivary gland, l.hp. Labium-hypopharynx. l.ep. Labrum-
epipharynx. mxp. Maxillary palp. as. (Esophagus, oc.n. Ocellar nerve.
ph.n. Pharyngeal nerve, p.c. Posterior cornu of fulcrum. P.O. Periopticon.
ps. Pseudotrachea. PI. Ptilinium. r.d.s. Retractor muscles of the discal
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 445
sclerites. r.f. Retractor muscle of the fulcrum, r.fu. Retractor muscle of
the furca. r.h. Retractor muscle of haustellum. r.r. Retractor muscle of
rostrum. S.O. Sub-cesophageal ganglion, sal.d. Common duct of the lin-
gual salivary glands, s.v. Valve of the common salivary duct. s.m. Muscle
controlling the valve of salivary duct. ih. Theca.
Fig. 2. — -Transverse section through the lower portion of the head-capsule,
showing the muscles and tracheal sacs in this region and the fulcrum in
section. (Camera lucida drawing.)
bp. Floor of pharynx, r.p. Roof of pharynx. tr.s. Tracheal sac. Other
lettering as in Fig. 1.
Fig. 3. — Transverse section through the lower half of the haustellum,
where the hypopharynx (hp.) has become free from the labium. (Camera
lucida drawing.)
di.l. Dilator muscles of the labium-epipharynx. tr. Trachea. Other
lettering as in Fig. 1.
Fig. 4. — Posterior view of the tracheal ducts which supply the cephalic
sacs and tracheee.
c.tr. Cervical tracheae which fuse above the oesophagus on the posterior
side of the cephalic ganglion, l.d. Lateral duct. m.d. Median dorsal duct.
tn.d. Tentorial tracheal ducts which spread out beneath the cephalic ganglion.
Fig. 5. — Lateral view of the terminal segments of the abdomen of the male
after their removal from the fifth segment.
vi, a.sp. and vii, a.sp. Sixth and seventh abdominal spiracles. Lettering as
in Fig. 10.
Fig. 6. — The thorax seen from the left side. The insertions of the larger
setai are shown; for the sake of clearness the sclerites of the wing- base are
omitted.
a.th. Anterior thoracic spiracle, ca. Costa. cp. Intermediate coxal
plates, ep'., ep". Epimera of the meso- and meta-thoracic segments, eps'.,
eps"., eps'". Episterna of the pro-, meso-, and meta-thoracic segments, hal.
Haltere. hu. Humerus. Ip. Lateral plate of mesostemum. lp.sc. Lateral
plate of postsculellum. mph. Mesophragma. mpsc. Median plate of post-
scutellum. mn. Metanotum. ms. Mesostemum. mis. Metasternum. p.th.
Posterior thoracic spiracle, pi. Parapterm. pr.n. Pronotum. prs. Pre-
scutum of mesothorax. sc. Scubum. sell. Scutellum.
Fig. 7. — Penis seen from the right side after it has been removed from
within the terminal abdominal segments.
i.ap. Inferior apophysis, th.p. Theca of penis, p.gl. Glans. s.ap. Supe-
rior apophysis. Other lettering as in Fig. 9, etc.
Fig. 8. — Abdomen of female showing the extended ovipositor.
V, d. to ix, d. Fifth to ninth dorsal arches or plates of the abdomen. V, v.
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446
0. GOIIDON HEWITT.
to viii, v. Fifth to eighth ventral plates or arches, su.p. The suranal plate
(ninth dorsal arch).
The anus is situated between the two lateral terminal tubercles.
Fig. 9.— Dorsal view of the penis and the ventral half of the terminal
abdominal segments. The median portion of the eighth dorsal arch has been
removed, leaving the lateral portions attached to the body of the penis (c.pe.)
and the ventral arch of the seventh segment (vii, v.).
Lettering as in Pig. 10.
Fig. 10. — The posterior end of the abdomen of the male seen from behind,
showing the pronounced sinistral asymmetry.
v, d. to viii, d. Fifth to eighth dorsal plates or arches, v, v. to viii, v. Fifth
to eighth ventral plates or arches, an. Anus. g.a. Aperture of genital
atrium, p.f. Primary forceps.
PLATE 24.
Fig. 11. — Nervous system. The very fine nerve which runs along the
dorsal side of the oesophagus to the proventricular ganglion {Pv.g., Fig. 20)
has been purposely omitted.
ab.n. Abdominal nerve, ac.ms. Accessory mesothoracic dorsal nerve, ac.ml.
Accessory metathoracic dorsal nerve, cer.n. Cervical nerves, cn. Cephalo-
thoracic nerve cord. O.P. Optic peduncle. pr.cr.,ms.cr.,mt.cr. Pro-, meso-,
and mela-thoracic crural nerves, pr.d., ms.d., mt.d. Pro-, meso-, and meta-
thoracic dorsal nerves.
Pig. 12. — Thoracic compound ganglia. Left aspect.
Lettering as in Figs. 11 and 14.
Pig. 13. — The tracheal sacs supplied by the anterior thoracic spiracle (a.t/i.).
In this figure the tracheal sacs supplied by the posterior thoracic spiracle and
the sterno-dorsales muscles of the left side have been removed. The left side
of the head and proboscis have also been removed. The first abdominal seg-
ment has been removed to show the large abdominal air sacs (ab.s.) and an
abdominal trachea which is supplied by the second abdominal spiracle (a.sp.).
a.cs. Anterior cephalic sac. a.v.s. Anterior ventral thoracic sac. c.lr.
Cervical tracheal duct. d.c. Dorsal cephalic sac. do. Dorsales muscles.
II. Haustellum. l.tr.s. Longitudinal tracheal sac. p.c.s. Posterior cephalic
tracheal sacs, p.v.s. Posterior ventral thoracic sac. p.op. Periopticon.
Eos. Rostrum, v.c.s. Ventral cephalic sac.
Fig. 14. — Thoracic compound ganglion after the removal of the cortex.
Seen from the ventral side. This and Fig. 12 were drawn from models re-
constructed from sections.
Pr.G., Ms.G., Mt.G. Pro-, meso-, and meta-thoracic ganglia. A.G. Abdo-
minal ganglion. Other lettering as in Fig. 11.
Fig. 15. — The tracheal sacs supplied by the posterior thoracic spiracle.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 447
In this figure the left side of the thorax has been removed, together with the
wing muscles and the posterior sterno-dorsales. It must be imagined that
this figure is superimposed on Fig. 13.
do. Dorsales. l.lh.s. Lateral thoracic sac. m.v.s. Median ventral sac.
v.l/i. Posterior thoracic spiracle, sc.s. Scutellar sac. st.do. Sterno-dorsales.
Fig. 16. — Wing. The nervures are drawn slightly thicker than they
naturally are.
an. Anal lobe. al. Alula, as. Antisquama. A. Anal cell. Av Anal
nervure. On. Cubital cell. 1 Cu. First cubital cell. cu-a. Cubito-anal trans-
verse nervure. Cx. Costa. C. Costal cell. 1 C. First costal cell. M. Medial
cell. m.cu. Medio-cubital transverse nervure. m. Medial transverse nervure.
2 M1, First and second second medial cells. M 1+2. Medial longitu-
dinal nervure. Mi + Cu. Medio-cubital longitudinal nervure. R. Radial
cell. Rl to 224+5. Radial longitudinal nervures. Sc. Subcostal cell.
Scv Subcosta.
PLATE 25.
Fig. 17. — The alimentary canal as it is seen on dissection from the dorsal
side. The malpighian tubes have been omitted, and also the distal portion of
the lingual salivary gland (s.lg.) of the right side. The duct of the crop (Cr.)
is shown by the dotted line beneath the proventriculus (Po.) and ventriculus
(Fen.).
p.int. Proximal intestine, d.int. Distal intestine, reel. Rectum.
Fig. IS. — Portion of a transverse section of the oral lobes, showing the two
types of gustatory sense organ, etc.
g.s. Gustatory seta. g.p. Gustatory papilla, hy. Hypodermis under which
lies a pigmented layer, p.s. Pseudo-trachea in section, s.g.p. Sensory bulb
of gustatory papilla, sp. Sensory bulb of gustatory seta, tr. Trachea.
Fig. 19. — Transverse section of labial salivary gland, to show the structure
of the gland cells (g.c). (Camera lucida drawing.)
hy. Hypodermis. ic.d. Intracellular duct. p.s. Pseudo-trachea, od.
Opening of intracellular duct into the permanent vacuole (vac.) of the gland
cell.
Fig. 20. — Section through the proventriculus and the anterior end of the
ventriculus, to show the structure of the proventricular plug (Pv.p.) and the
ducts of the oesophagus (ces.) and crop (d.cr.). (Camera lucida drawing.)
Fig. 21. — The posterior region of the alimentary canal, to show the rectal
glands (rect.gl.) with their tracheal supply, the origin of the malpighian tubes
(malp.), and the position of the rectal valve indicated at X .
Fig. 22. — Transverse section of the lingual salivary gland, showing the
fibrillar character of the gland cells. X 220. (Camera lucida drawing.)
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448
C. GORDON HEWITT.
PLATE 26.
Eig. 23. — Female reproductive organs in situ; the left ovary and the
viscera have been removed. The ovipositor (ovp.) is shown retracted, in
which state the common oviduct (c.o.d.) is doubled back.
ac.g. Accessory gland, a.c.v. Accessory copulatory vesicle, ov. Ovary
composed of about seventy ovarioles, and containing ova in various stages of
development, ov.d. Oviduct, retr.m. Retractor muscles of the ovipositor.
Sp. Spermatheca; or vesiculse seminales.
Fig. 24. — The male reproductive organs. They have been slightly spread
out, and the rectum (reel.) has been turned over to the right side.
d.e. Ejaculatory duct. e.a. Ejaculatory apodeme. e.s. Ejaculatory sac.
te. Testis, v.d. Vas deferens.
Eig. 25. — Vertical section of one of the rectal glands, to show its struc-
ture. X 56. (Camera lucida drawing.)
sh. Perforate chitinous sheath, r.gl. Gland cell. tr. Trachea.
Eig. 26. — Terminal region of the female reproductive organs, showing the
accessory glands, etc.
sac. Sacculus. vag. The muscular vagina which evaginates during copula-
tion; a pair of retractor muscles are shown. Other lettering as in Fig. 23.
C.GIH. Sol.
BRITISH
C G H del
MUSCA
3 M E STI C A
HuG\,Lithr London
C.G-.H. a«i
M U5CA
MESTICA
17.
C G.H. del
M (JSC A D
El S T I C A
Huth.Lilhr London
Hutfi , la thr London.
MUSCA DOME STICA.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 495
The Structure, Developmeut, aud Bionomics of
the House-fly, Musca domestica, Linn.
Part II. — The Breeding Habits, Development, and the Anatomy
of the Larva.
By
€. Gordon Hewitt, M.Sc,
Lecturer in Economic Zoology, University of Manchester.
With Plates 30—33.
Contents.
PAGE
I. Introduction
II. Breeding Habits
III. Factors and Rate of Developmeut .
IV. Development :
496 (56)
497 (57)
500 (60)
1. Copulation
505 (65)
506 (66)
506 (66)
508 (68)
2. Egg
3. Larva
4. Pupa
V. Anatomy of the Larva :
1. External Structure
2. Muscular System .
3. Nervous System .
4. Alimentary System
5. Respiratory System
6. Vascular System and Body Cavity
7. Imaginal Discs
510 (70)
513 (73)
519 (79)
523 (83)
528 (88)
530 (90)
532 (92)
535 (95)
538 (98)
VI. Summary
VII. Literature
VOL. 52, PART 4. — NEW SERIES.
38
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196
0. GORDON HEWITT.
I. Introduction.
In the present paper, which is the second of the series of
three, the breeding habits and development of M. domestica
and the anatomy of the mature larva will be described. Its
publication has been delayed owing to the fact that I wished
to make the observations on the breeding habits and life-
history as complete as possible. With the recent appearance
of two short papers by Newstead (1907) and Griffith (1908),
many of whose observations, to which I shall refer later, are
confirmatory of my own results, we now have a more com-
plete account of the breeding habits of this insect.
The auatomy of the larva has been described in a similar
manner to that of the fly (1907). I have refrained in this
paper from giving a detailed account of the embryology and
the development of the imaginal discs, as these are separate
and specialised studies, and would have resulted in too great
a digression from the plan originally adopted.
The methods used were the same as those previously
employed. The anatomical structures were studied with the
aid of the Zeiss binocular dissecting microscope, and the
drawings were made from the dissections. The latter were
confirmed by means of serial sections. Too much stress
cannot be laid on the importance of employing both these
methods where possible, as it frequently happens that mistakes
are made iu investigating by one method only, which would
be unrectified were not the other employed in confirmation.
I wish to thank the Council of the Manchester University
for providing me with a suitable experimental greenhouse
and apparatus for the experimental portion of this investiga-
tion ; the absence of such facilities would have been a severe
handicap. The outdoor observations on the breeding habits
have been made during the last few years in Manchester and
the surrounding district.
The third paper, which will conclude this study of M.
domestica, will deal with the bionomics of the fly, its para-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 497
sites and its relation to man, and certain of its allies which
frequent houses will be considered.
II. Breeding Habits of M. domestica.
The development of M. domestica was first described by-
Carl de Greer (1776) j but, although he stated that it developed
in warm and humid dung, he did not give the time occupied
by the different developmental stages. He refers to the
enormous quantities of flies occurring from July to August.
His statement concerning their development is especially
interesting, as he appears to be the first investigator who
called attention to what I consider to be one of the most
important factors in the development of the fly, namely, the
process of fermentation occurring in the substance in which
development is taking place. He says (p. 76), "Les larves
de cette espece vivent done dans le fumier, mais uniquement
dans celui qui est bien chaud et humide, ou pour mieux
dire qui se trouve en parfaite fermentation" (the italics
are mine). Since the completion of my own investigations
on the development, all of which indicated the importance of
this factor fermentation, Newstead (1. c.) has come to the
same conclusion. The work of Keller (1790), to which
reference was made in the first part of this memoir, contains
many interesting and careful observations on the breeding
habits of the " Stubenfliege." He found that the eggs
hatched from twelve to twenty-four hours after deposition.
He reared the larvas in decaying grain where, no doubt,
fermentation was taking place; also in small portions of
meat, slices of melon, and in old broth. His observations
are extremely interesting, and, excluding mistakes which
were due to the lack of modern apparatus, his account is still
a valuable contribution to our knowledge of the subject.
Bouche (1834) describes the larva? as living in horse-manure
and fowl-dung, especially when warm. He does not give the
time occupied by the earlier developmental stages, but states
that the pupal stage lasts from 8 — 14 days. Packard (1874)
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498
C. GORDON HEWITT.
was the next to study the development and working in the
United States of America at Salem, Mass., he found that
the larva) emerge from the eggs twenty-four hours after
deposition; the times taken by the three larval stages — for
he found that there were two larval ecdyses — were : first,
about twenty-four hours ; the second stage, he thought, was
from twenty-four to thirty-six hours; and the third was pro-
bably three or four days ; the entire larval life being from
five to seven days. The pupal stage was from five to seven
days, so that in August, when the experiments were carried
on, the time from hatching to the exclusion of the imago
was ten to fourteen days. Taschenberg (1880) incorporates
the work of Keller and Bouche, and does not appear to add
anything of importance to the facts already mentioned. He
states that the female flies deposit their eggs in damp and
rotting food-stuffs, bad meat, broth, slices of melon, dead
animals, cesspools, and manure-heaps. He further says that
they have also been observed laying their eggs in spittoons
and open snuff-boxes. With reference to the last statement,
I find that the larvae will feed on expectorated matter mixed
with a solid substance, such as earth, if they ai*e kept warm,
though they cannot feed on salivary sections merely ; but,
although flies might ini providently deposit their eggs in an
open snuff-box, the larvae would soon perish on hatching on
account of the dry conditions.
Howard (1896 — 1906) first studied the breeding habits of
the fly in 1895 in Washington, U.S.A., and he described
them in 1896, and more fully subsequently. He found that
they could be rarely induced to lay their eggs in auything
but horse-manure and cow-dung, and that they preferred the
former. The periods of development he found were as
follows : — from the deposition of the egg to the hatching of
the larva about eight hours ; the first larval stage one day;
second larval stage one day ; third larval stage — that is, from
the second ecdysis to pupation— three days, and the flies
emerged five days after the pupation of the larvae, thus making
the whole period of development about ten days. The same
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 499
author in a valuable study of the insect fauna of human excre-
ment (1900), describes experiments in which he was successful
in rearing M. domestica from human excrement both in the
form of loose fasces and in latrines. Newstead (1. c), in
addition to confirming- some of my observations, also found
the larva? in spent hops, dirty beddings from rabbits and
guinea-pigs, bedding from piggeries, and in the rotten flock
beds and straw mattresses which, I suppose, were either in,
or from, ashpits, and fouled with excremental products,
although it is not stated. He appears to have overlooked
some of the work of previous investigators.
My studies of the breeding habits of M. domestica were
initiated in 1905, and were continued in 1906, when a short
account of some of the results was published (1906). The
shortest time which I then obtained for the development of
any batch of larvae was twenty days, although, taking the
shortest period obtained for each developmental stage in the
series of experiments, the development could have been com-
pleted in fifteen days under suitable conditions. In the
summer of 1907 I continued my experiments on a much larger
scale and under better circumstances, and the following are
the results of my experiments and outdoor observations :
The larvae have been successfully reared in horse-manure,
cow-dung, fowl-dung, human excrement, both as isolated
faeces and in ashes containing or contaminated with excrement,
obtained from ashpits attached to privy middens, and such
as is sometimes tipped on to public tips. I found that horse-
manure is preferred by the female flies for oviposition to all
other substances, and that it is in this that the great majority
of larvaa are reared in nature ; manure-heaps in stable yards
sometimes swarm with the larvas of M. domestica. It was
also found that the larvae will feed on paper and textile
fabrics, such as woollen, cotton garments, and sacking which
are fouled with excremental products if they are kept moist
and at a suitable temperature. They were also reared on
decaying vegetables thrown away as kitchen refuse, and on
such fruits as bananas, apricots, cherries, plums, and peaches,
(CO)
500
0. GORDON HEWITT.
which were mixed, when in a rotting condition, with earth to
make a more solid mass. Although they can be reared in
such food-stuffs as bread soaked in milk and boiled egg, when
these are kept at a temperature of about 25° C, I was unable
to rear them to maturity in cheese, although they fed on the
substances for a few days and then gradually died, my failure
may have been due to the nature of the cheese which was
used, only one kind being tried. In addition to rearing the
larvae on isolated human feces, such as are frequently found
in insanitary court-yards and similar places, they were found
in privy middens, and also on a public tip among the warm
ashes and clinker where the contents of some privy middens
had also evidently" been emptied; I bred the flies out from
this material.
III. Factors of Development.
The rate of development depends primarily on the tempera-
ture of the substance on which the larvae are feeding. This
was shown in my experiments in which the larvae were reared
in horse-manure kept in a moist condition in an incubator at
a constant temperature of 35° C. At this temperature the
development is completed in eight to nine days. I found that
a higher temperature of 40° C. was too great for the larvae as
they were simply cooked and perished at such a temperature.
This has been confirmed by Griffith (I.e.), who found that
the life-history was completed in the same time on incubating
at a temperature of about 22° — 23° 0. I do not think that a
shorter time than this for the development — that is, from the
deposition of the egg to the emergence of the perfect insect
from the pupae — will ever occur in this country, as we rarely
enjoy prolonged spells of hot weather which would bring
about such conditions as regards temperature. It is interest-
ing to note that Smith (1907) gives the time of development
in horse-manure in India under natural conditions as eight
days; he also bred M. domestica from an artificial latrine
containing human excreta mixed with earth, which confirms
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 501
English observations for India. In England, during a period
of extremely hot weather, flies might develop in about nine
days, but such a rate of development would not usually occur,
nevertheless, as I shall show in the concluding part of this
memoir, such a contingency must be guarded agaiust. Larvae
reared in the open air in horse-manui"e which had an average,
but not a constant, daily temperature of 22*5° C, occupied
fourteen to twenty days in their development according to the
air temperature.
The effect of the character of the food on which the rate of
development also depends is well shown by a comparison of
the times of the developmental periods in two of the experi-
ments where the average daily temperature was practically
the same, namely, 19-3° C. and 20,5° C. In the former experi-
ment, in which human faeces were used, the development was
completed in twenty days, and in the latter, in which bananas
were used, the development occupied twenty-seven days ; the
time was rather lengthened in both cases by the fact that the
larval food was rather dry, but equally dry in both experi-
ments as they were kept together ; had more moisture been
present the times would probably have been correspondingly
shortened.
It was experimentally proved that when larvae were reared,
in batches on the same kind of food material with conditions,
as regards temperature the same, the developmental period
was longer for those larvae which were subject to dry condi-
tions than for those subject to moist conditions. In an
experiment at an average temperature of 22° C. larvaa reared
on horse-manure which was kept in a rather dry condi-
tion took thirty days to complete the development, and
another batch at the same temperature, but on horse manure
which was kept moist, the development was completed in
thirteen days. Under similar conditions, with regard to tem-
perature, the rate of development is directly proportional to
the condition of the food as regards moisture. Dry conditions
not only retarded development in some of my experiments to
five and six weeks, but also tended to produce flies of sub-
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502
0. GORDON HEWITT.
normal size. Moisture is necessary for the development, and
if the food becomes too dry the result is fatal, as the larva)
perish.
A fourth and a most important factor affecting development
and one intimately connected with the previous factors — tem-
perature, character of food, and moisture — is that of fermenta-
tion, to which reference has already been made. This process
appears to take place in the substances on which the larva?
best subsist. Whether the suitability of the food is deter-
mined by the nature of its fermentation is a point which
I was unable to determine, but which I am inclined to believe.
I feel certain, however, that the calorific property of fermenta-
tion is the most important part of this process on account of
its direct relation to the time of development ; the endogenous
heat of exci'emental products and decaying substances acting
either in addition to, or independently of, the temperature of
the surrounding air is of great advantage in accelerating the
rate of development.
The Eate of Development. — This was never found to
be less than eight days, and was more usually twelve to
twenty days owing to the fact that a continuously high air
temperature was not maintained for any sufficient length of
time; with such a continuous period of hot weather the
development would take about ten to twelve days, and in
very great heat might be completed in a day or two less as
the internal temperature of the breeding places, such as
manure-heaps is usually higher than the temperature of the
air. It mnst be remembered, however, that except by incu-
bation it is difficult to experimentally imitate such natural
conditions as occur in a manure-heap or privy midden, where,
owing to a larger amount of material, a higher constant
temperature is maintained. All experimental results except
those of incubation tend to give a long rather than a short
rate of development. In many cases where the average tempe-
rature was 20° C, but the food material rather dry, the de-
velopmental period was about three weeks, and where the
temperature was low and the food became dry it extended to
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 503
as much as six weeks, the greater time being spent in the pupal
state which was sometimes of three or four weeks duration.
In no case was I able to keep the pupa? through the winter
as I have been able to keep the pupa3 of Stomoxys
calci trans and other forms.
My experiments and observations poiut to the fact that in
the presence of suitable larval food, such as excremental
matter or decaying and fermenting food materials in a moist
and warm condition, the female flies would lay their eggs
and the larvas would develop if the temperature of the air
were sufficiently high for the prolonged activity of the flies.
In winter this last condition is not naturally satisfied, but
under such conditions as are found, for example, in warm
restaurants and kitchens, stables and cowsheds, female flies
may be often found during the winter. On dissecting such
flies I have found mature ova in the ovaries, and living
spermatozoa in the spermatheca?, which facts support this
view. Griffith (1. c.) has succeeded in rearing batches of
eggs in November, December, and early January under
artificial conditions, which further proves their ability, given
the necessary conditions as regards temperature, to breed
during the winter months. In this country M. domestica
breeds, as a rule, from June to October, and the greatest egg-
laying activity prevails in August and September. As I have
already contended, and as Griffith has shown, they may breed
at other times if the necessary conditions are present ; I have
obtained eggs from flies caught in restaurants in December;
Keller also mentions the fact that he obtained eggs in January.
These facts may account for the rapid appearance of flies in
the early summer. It is not unlikely that the flies which
survive the winter months, which many spend in a dormant
condition if they are not fortunate enough to remain active
in a warm restaurant or stable, lay their eggs, almost
immediately on renewing their activity, in such places as
manure-heaps which are kept, as is often the case in towns,
under cover, and which are consequently warmer externally
than those in the open. In this way a large number of flies
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0. GORDON HEWITT.
would be reared and ready to assume their customary activity
under the benign influence of the sunny days of June.
I have made many experiments with a view to finding out
the rapidity with which house-flies breed. Anyone who has
endeavoured to keep flies alive in an enclosed space will
appreciate the difficulty of the task, those who have not done
so would hardly realise it. Fewer insects seem less tenacious
of life when enclosed even in a comparatively large enclosure
of six or nine cubic feet. It is a remarkable fact, as one
would imagine a priori that these insects, flying about
everywhere as they do, could be easily kept in a roomy cage
if given the necessary food and water. This, however, has
not been the case in my experience ; the longest period which
I have been able to keep them in captivity in summer is
seven weeks. I am pleased to find that Griffith has succeeded
in keeping a male fly sixteen weeks, and has obtained four
batches of eggs from females in captivity. In one of my
experiments I was successful in obtaining flies of the second
generation bred in captivity. I found that the flies became
sexually mature in ten to fourteen clays after their emergence
from the pupal state and, four days after copulation, they
began to deposit their eggs, that is, from the fourteenth day
onwards from the time of their emergence.
From these results it may be seen that in very hot weather
the progeny of a fly may be laying eggs in about three weeks
after the eggs from which they were hatched had been de-
posited. As a single fly lays from 120 — 150 eggs at one time
and may deposit five or six batches of eggs during its life, it
is not difficult to account for the enormous swarms of flies
that occur in certain localities during the hot summer months,
and algebraical calculations are not required to more vividly
impress the fact.
IV. Development.
As I have already stated, M. domestica may become
sexually mature in about ten to fourteen days after emer-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 505
gence from the pupal case, and at this time they may he seen
copulating.
1. The copulation of M. domestica appears to have
been first described by Eeamur (1738). It has been carefully
described recently by Berlese (1902), whose observations my
own confirm. The male may perform a few tentative opera-
tions before copulation takes place, and these have been mis-
taken for the actual act. The male alights on the back of
the female by what appears to be a carefully calculated leap
from a short distance, and this act seems to indicate a faculty
on the part of the fly of being able to judge distance. It
then caresses the head of the female, bending down at the
same time the apical portion of the abdomen. The male fly
is, however, peculiarly passive during the operation, its influ-
ence apparently being only tactual, it is only when the female
exerts her ovipositor and inserts it into the genital atrium of
the male that copulation can successfully take place. When
the ovipositor has been inserted into the genital atrium of the
male, the accessory copulatory vesicles of the female become
turgid and retain the terminal segment in this position, in
which the female genital aperture is situated opposite to the
male genital aperture at the end of the penis, the latter
depending from the roof of the genital ati-ium. (This will be
better understood by reference to the figures of these parts
in Part I of this Memoir). The attachment of the penis to
the female genital aperture is made still firmer by the dorsal
sclerites of the eighth segment of the female and the ventral
sclerites of the seventh segment, the so-called secondary for-
ceps of the male acting respectively above and below the
penis. The fifth ventral segment, or primary forceps of the
male, assist the accessory copulatory vesicles of the female in
preventing the withdrawal of the ovipositor before the sper-
matozoa have been injected into the female genital aperture,
by which way they enter the spermathecae. The whole act
may be over in a few moments or they may remain in coitu
for several minutes.
The eggs are laid a few days after copulation ; I found
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506
0. GORDON HEWITT.
tbat oviposition may take place as early as the fourth day ;
Taschenberg (t. c.) states that the female lays on the eighth
day after copulation. When about to deposit its eggs the fly
alights on the substance which it selects as a suitable nidus
and, if possible, crawls down a crevice out of sight. There
it lays its eggs in clumps ; they are usually placed vertically
on their posterior ends and closely packed together. During
a single day, if undisturbed, a fly may lay the whole batch of
eggs which are mature in the ovaries and which may number,
I find from actual count, from 120 — 150.
2. The Egg.— The egg of M. domestica (PI. 30, fig. 1)
measures 1 mm. in length, sometimes slightly less. It is
cylindrically oval ;"one end, the posterior, is broader than the
other, towards which end the egg tapers off slightly. The
outer covering or chorion is pearly white in colour, the
polished surface being very finely sculptured with minute
hexagonal markings. Along the dorsal side of the egg are
two distinct curved rib-like thickenings having their concave
faces opposite. In the hatching of the eggs which I have
observed, the process was as follows : — A minute split ap-
peared at the anterior end of the dorsal side to the outside of
one of the ribs ; this split was continued posteriorly (fig. 2),
aud the larva crawled out, the walls of the chorion collapsing
after its emergence. The time of hatching varies according
to the temperature. With a temperature of 25°0. — 35°C. the
larvas hatch out from eight to twelve hours after the deposition
of the eggs ; at a temperature of 15°C. — 20°O. it takes about
twenty-four hours, and if kept as low as 10°C, two or three
days elapse before the larvse emerge.
3. The Larva. — First larval stage or first instar.
— The newly-hatched larva (fig. 8), measures 2 mm. in length.
It contains the same number of segments as the mature larva
and at the anterior end of the ventral surface of each of the
posterior eight segments there is a spiny area (sp.). The
posterior end is obliquely truncate, and bears centrally the
only openings of the two longitudinal tracheal trunks, each
trunk opening to the exterior by a pair of small oblique slit-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 507
like apertures situated on a small prominence (p.sp.). There
are no anterior spiracular processes in the first larval stage.
The oval lobes are relatively large aud on the internal ventral
surface of each there is a small T-shaped sclerite (fig, 13, t.s.).
These sclerites lie lateral to the falciform mandibular sclerite
(m.s.). The cephalopharyngeal skeleton of the first larval
instar is slender and, in addition to the sclerites already men-
tioned, consists of a pair of lateral pharyngeal sclerites or
plates {l.p-) deeply incised posteriorly, forming well pro-
nounced dorsal and ventral processes. The lateral plates are
connected antero-dorsally by a curved dorsal sclerite (d.p.s.).
The anterior edges of the lateral plates are produced ventrally
into a pair of slender processes (h.s.), the anterior portions of
these processes, which represent the hypostomal sclerite, are
involute and articulate with the mandibular sclerite. The
alimentary canal of the first larval instar is relatively shorter
than that of the adult, and consequently it is not so convo-
luted ; the salivary glauds are proportionately large.
The first larval instar may undergo ecdysis as early as
twenty hours after hatching, but it is usually from twenty-
four to thirty-sis hours that the ecdysis takes place : under
unfavourable conditions with regard to the factors governing
the development, the first larval instar sometimes lasted three
or four days. Ecdysis begins anteriorly, and the larva not
only loses its skin but also the cephalopharyngeal sclerites
which are attached to the stomodasal portion of the ecdysed
chitinous integument; the chitinous lining of the proctodteal
portion of the alimentary tract is also shed.
The second larval stage or second instar. This
stage is provided with a pair of anterior fan-shaped spira-
cular processes similar to those of the mature larva. The
posterior spiracular orifices are shown in fig. 12. They are
slit-like apertures rather similar to those of the first instar
but larger in size. The cephalopharyngeal skeleton is thick-
ened and less slender in form than that of the first instar. It
resembles the cephalopharyngeal skeleton of the mature larva
except that the posterior sinuses of the lateral pharyngeal
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508
0. GORDON HEWITT.
sclerites are much deeper, thus making the dorsal and ventral
posterior processes more slender than in the mature larva.
The second larval instar may undergo ecdysis in twenty-four
hours at a temperature of 25° — 35°C, but under cooler con-
ditions or with a deficiency of moisture the period is pro-
longed and may take several days.
The third larval stage or third instar, which is the last larval
stage, grows rapidly. The anatomy of this the mature larva
will be fully described. Larvaa incubated at a temperature
of 35°C. complete this larval stage and pupate in three to
four days, on the other hand, under less favourable develop-
mental conditions, it sometimes extended over a period of
eight or nine days. Incubated larvas cease feeding at the end
of the second day of this stage and gradually assume a creamy
colour, which colour is due to the large development of the
fat body and to the histolytic changes which are taking place
internally ; larvae dissected at this stage contain a very large
amount of adipose tissue cells. Between the third and fourth
day the larva contracts to form the pupa.
4. The Pupa. — The process of pupation may be completed
in so short a time as six hours. The larva contracts, the
anterior end especially being drawn in, with the result that a
cylindrical pupal case is formed (fig. 15), the posteiuor region
being very slightly larger in diameter than the anterior; the
anterior and posterior extremities are evenly rounded. The
average length of the pupa is 6'3 mm. Owing to the with-
drawal of the anterior segments the anterior spiracular pro-
cesses (a.sp.) are now situated at the anterior end, and the
posterior spiracles {p.sp.) form two flat button-like promi-
nences on the posterior end. The pupa changes from the
creamy-yellow colour of the larva to a rich dark brown in a
few hours. As the last larval skin has formed the pupal case,
it being a coarctate pupa, in addition to the persistance of
the spiracular processes the other larval features such as
spiny locomotory pads can be seen.
During the first twelve hours or so of pupation the larva
loses its tracheal system, which appears to be withdrawn
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 509
anteriorly and posteriorly, the latter moiety being the larger ;
the discarded larval tracheal system lies compressed against
the interior of the pupal case (l.tr.). Communication with
the external air is formed for the nymphal1 developing
tracheal system by means of a pair of temporary pupal
spiracles, which appear as minute spine-like lateral projec-
tions between the fifth and sixth segments of the pupal case
(n.sp.). Each of these communicates with a knob-like spira-
cular process (fig. 10, n.sp.) attached to the future pro-
thoracic spiracle of the fly. The proctodseal and stomodaeal
portions of the alimentary tract are also withdrawn, and with
the latter the cephalo-phaiwngeal skeleton, which lies on its
side on the ventral side of the anterior end of the pupal case.
The histogenesis of the nymph is extremely rapid, so that
at the end of about thirty hours, in the rapidly developing
specimens, it has reached the stage of development shown in
fig. 10, in which most of the parts of the future fly can be
distinguished although they are ensheathed in a protecting
nymphal membrane'. The head, which with the thorax has
been formed by the eversion of the cephalic and thoracic
imaginal discs from their sacs, is relatively large : two small
tubercles (an.) mark the bases of the antennas. The pro-
boscis is enclosed in a lai'ge flat sheath which at this period
appears to be distinctly divided into labral (Ibr.) and labial
(lb.) portions. In a short time the parts of the proboscis are
seen to develop in these sheaths (fig. 11). The femoral and
tibial segments of the legs are closely adpressed and lie
within a single sheath. The wings (w) appear as sac-like
appendages, and, as the nymphal sheath of the wing does not
grow beyond a certain size, the wing develops in a slightly
convoluted fashion by means of a fold which appears in the
costal margin a short distance from the apex of the wing.
With a constant temperature of about 35° C, or even less,
the exclusion of the imago may take place between the third
1 The word " nymph " is used here to designate that stage in the develop-
ment which begins with the appearance of the form of the future fly, and
ends when the exclusion of the imago takes lace.
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510
C. GORDON HEWITT.
and fourth day after pupation, but it is more usually four or
five days as the larvae, when about to pupate, leave the hotter
central portion of the mass in which they have been feeding and
pupate in the outer cooler portions : this outward migration
may be a provision for the more easy emergence of the ex-
cluded fly from the larval nidus. In some cases the pupal
stage lasts several weeks, but I have never succeeded in
keeping pupae through the winter.
When about to emerge, the fly pushes off the anterior end
of the pupal case in dorsal aud ventral portions by means of
the inflated frontal sac, which may be seen extruded in front
of the head above the bases of the antennas. The splitting
of the anterior end of the pupal case is quite regulai*, a cir-
cular split is formed in the sixth segment and two lateral
splits are formed in a line below the remains of the anterior
spiracular processes of the larva. The fly levers itself up out
of the barrel-like pupa and leaves the nymphal sheath. With
the help of the frontal sac which it alternately inflates and
deflates it makes its way to the exterior of the heap and
crawls about while its wings unfold and attain their ultimate
texture, the chitinous exoskeleton hardening at the same
time ; when these processes are complete the perfect insect
sets out on its career.
V. The Larva op Mdsca domestica.
1. External Features. — The external appearance of the
typical acephalous muscid larva or " maggot " (fig. 5) is well
known. It is conically cylindrical. The body tapers off
gradually to the anterior end from the middle region. The
posterior moiety is cylindrical, and except for the terminal
posterior segment the segments are almost equal in diameter.
The posterior end is obliquely truncate. The cuticular in-
tegument is divided by a number of rings ; this ringed con-
dition is brought about by the insertion of the segmentally-
arranged somatic muscles the serial repetition of which can
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 511
be clearly understood by reference to fig. 16. The average
length of the full-grown larva of M. domestica is 12 mm.
The question as to the number of segments which constitute
the body of the muscid larva is a debated subject. I have,
however, taken as my criterion the arrangement of the
somatic musculature. Newport (1839) considered that the
body of the larva of Musca vomitoria consisted of fourteen
segments, but if the anterior portion of the third segment,
that is, my first post-oral segment, is included, there were
fifteen, to which view he appeared to be inclined. Counting
theanterior segment or " head " as the first, Weismann (1863
and 1864) considers that the body is composed of twelve seg-
ments. Brauer (1883) is of the opinion that there are twelve
segments, but that the last segment is made up of two ;
Lowne follows this view in his description of the blow-fly
larva and considers that there are fifteen post-oral segments.
I am unable to accept Lowne's view. Counting the proble-
matical cephalic segment, for which I shall use Henneguy's
(1904) term " pseudo-cephalon," as the first segment, I
believe that it is succeeded by twelve post-oral segments,
making thirteen body segments in all, which is the usual
number for dipterous larvas as Schiner (1862) has also pointed
out. My study of the somatic musculature, as I shall show,
indicates the duplicate nature of the apparent first post-oral
segment, so that the apparent second post-oral segment (iv),
that is, the segment posterior to the anterior spiracular pro-
cesses, is really the third post-oral segment or fourth body-
segment.
The cephalic segment cannot be considered as homologous
with the remaining twelve segments, which are true segments
of the body as shown by their musculature and innervation.
This segment (fig. 9, i), for which Henneguy's term "pseudo-
ccphalon " is very suitable, probably represents a much reduced
and degenerate cephalic segment, its present form being best
suited to the animal's mode of life. We may consider the
greater part of the cephalic segment of the larva as having
been permanently retracted within the head; this is shown by
vol. 52, part 4. 39
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512
0. GORDON HEWITT.
the position of the pharyngeal skeleton, to the whole of which
the name " cephalo-pharyngeal skeleton " has been given. All
that now is left of the cephalic segment consists of a pair of
oral lobes, whose homology with the maxilla? is very proble-
matical, and at present is not safely tenable. On the dorsal
side the oral lobes are united posteriorly. Each bears two
conical sensory tubercles (o. t.), which are situated, the one
dorsally, and the other anterior to this and almost at the apex
of the oral lobe. The ventral and ventro-lateral surfaces of
the oral lobes are traversed by a number of channels, which
will be described later.
The post-cephalic segment, which is composed of the first
and second post-oral segments and represents the second and
third segments of the body, is conical in shape. The first
post-oral segment (ii), to which Lowne gave the name
" Newport's segment," is limited posteriorly by a definite
constriction and is covered with minute spines. The second
post-oral segment bears laterally at its posterior border the
anterior spiracular processes (a. sp.) The remaining seg-
ments of the body — four to twelve — are on the whole similar
in shape. At the anterior edge of the ventral side of each of
the sixth to twelfth body-segments there is a crescentic pad
(fig. 5, sp.) bearing minute and recurved spines; these are
locomotory pads by means of which the larva moves forwards
and backwards. It is important to note that these pads are
situated on the anterior border of the ventral side of each
segment as they do not appear to have been carefully placed
in the previous figures of this species. In addition to these
spiniferous pads there are two additional pads of a similar
nature, one on the posterior border of the ventral side of the
twelfth body-segment, and the other posterior to the anus.
The terminal or thirteenth body-segment is obliquely trun-
cate, but the truncate surface, which occupies more than half
the posterior end of the larva, is not very concave as in the
blow-fly larva. It bears in the centre the two posterior
spiracles (fig. 3, p. sp.), which are described in detail with the
tracheal system. On the ventral side of the terminal segment
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 513
are two prominent anal lobes (fig. 5, an. I.), which, are impor-
tant agents in locomotion.
The cuticular integument is thin and rather transparent, so
that in the younger larvse many of the internal organs can be
seen through it. In older larvae the fat-body assumes large
proportions and gives the larva a creamy appearance, obscur-
ing the internal organs. The cuticle (fig. 14) is composed of
an outer rather thin layer of chitin (ct.), which is continuous
with the chitinous intima of the tracheae, and also with the
chitinous lining of the stomodieal and proctodaaal regions of
the alimentary tract. Below this layer there is a thicker
layer of chitin (ct/), which does not stain so deeply. In
places this lower layer is penetrated by the insertions of the
muscles. The cuticle lies on a layer of stellate hypodermal
cells (hy.), which are well innervated, and attain a large size
in the posterior segments of the body.
2. Muscular System.
The muscular system of the larva (PI. 31, fig. 16) consists of
a segmental series of regularly repeated cutaneous muscles,
forming an almost continuous sheath beneath the skin,
together with a set of muscles in the anterior segments of
the body which control the cephalo-pharyngeal sclei'ites and
pharynx. In addition to this there are a set of cardiac
muscles and the muscles of the alimentary tract.
I have been unable to find a detailed description of the
muscular system of the muscid larva, and I do not think that
Lowne's excuse for dismissing the cutaneous muscles of the
blow-fly larva with a very brief statement, because "the
details possess little or no interest," was justified, considering
how little is known about the muscular systems of insect
larvae, and constant reference to the classic work of Lyonet
(1762) on the caterpillar is not sufficient to satisfy the
inquiring student of to-day. The muscular system of the
larva, therefore, will be described in some detail.
Muscles of the body- wall. — The cutaneous muscles
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514
0. G0KD0N HEWITT.
are repeated fairly regularly from segments (by segments I
mean body-segments) four to twelve and a detailed descrip-
tion of the muscles of one of these segments will serve for the
rest. The muscles, though continuous in most cases from seg-
ment to segment, are attached to the body-wall at the junction
of the segments. The most prominent muscles are the dorso-
lateral oblique recti muscles. In segments six to twelve there
are four pairs each of external (ex. d. I.), and internal dorso-
lateral oblique recti (in. d. I.) muscles ; in segments four and
five there are five pairs of external and six pairs of internal
dorso-lateral oblique muscles. Ventral to these muscles are
four pairs of longitudinal ventro-lateral muscles (I. v. I.) ; the
muscle bands of the two more ventral pairs are double the
width of those of the two more lateral pairs. In the fifth seg-
ment there is only one of the more lateral pairs of the longi-
tudinal ventro-lateral muscles present, and in the fourth
segment only the two more ventral pairs remain. In addition
to these muscles there are two other pairs of oblique recti
muscles ; these are, a pair of ventro-lateral oblique muscles
(v. I. o.) and a pair of internal lateral oblique muscles (i. I. o.) ;
both of these are absent in the segments anterior to the sixth.
The foregoing muscles, namely the dorso-lateral oblique, the
internal lateral oblique, the ventro-lateral oblique and the
longitudinal ventro-lateral, by their contraction, bring together
the intersegmental rings and so contract the body of the larva.
Attached externally to the anterior ends of the longitudinal
ventro-lateral muscles are a number of pairs of ventral oblique
muscles (v. o.) ; they vary in number from two to eight pairs in
each segment. The number increases posteriorly from two
pairs in segment four to four pairs in segment five, five pairs
in segment seven, seven pairs in segment ten, eight pairs in
segment eleven; the number of pairs then decreases to six or
seven pairs in segment twelve. The more ventral pairs of
those muscles are not attached at their posterior ends to the
intersegmental ring but to the ventral wall of the segment
and no doubt assist in bringing forward the ventral spiniferous
pads. In segments four to twelve there are three pairs of
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STEUCTUliE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 515
lateral muscles (I. m.) situated next to the hypodeimis and
attached in a dorso- ventral position; these will assist in draw-
ing the dorsal and ventral regions of the segments together
and so increase the length of the larva. Between segments
four and five and the remaining segments to twelve there is,
on the intersegmental ring, a pair of lateral intersegmental
muscles (I. i. m.) ; these by their contraction bring about a
decrease in the size of the intersegmental ring and so assist
the lateral muscles in increasing the length of the larva.
The muscles of the last segment (xiii) are not regularly
arranged as in the preceding segments; they consist of three
main groups : (1) the recti muscles, which assist in contract-
ing the segments ; (2) the anal muscles (an. m.), which are
attached ventrally to tlie anal lobes (an. I.) ; and (3) the
dorso-ventral muscles (d. v.), which by their contraction
assist in lengthening the segment. In addition to these there
are certain small muscles in relation with the posterior
spiracles.
In the second and third segments the recti muscles are
reduced to four pairs and the attachment of the two lateral
and external pairs of muscles has led me to regard the
apparently single first post-oral segment as consisting of two
segments; it is not a single post-cephalic or pro-thoracic seg-
ment as it has been called. There is quite a distinct internal
division and the external constriction has been already
noticed. This view does not necessarily alter the homology
of the third segment, which may still be regarded as pro-
thoracic if this is desirable. The segment which I regard as
the second body-segment may be a rudiment of the cephalic
region which has been almost lost, and this loss, or, as I
prefer to regard it, this withdrawal of the head, only serves to
make any discussion as to the homologies of these anterior
segments with those of the adult extremely difficult, and, I
believe, at present valueless. Further, comparative studies
of the larvae of the calyptrate inuscidas are necessary before we
can arrive at any definite conclusions concerning the com-
position of the bodies of these larval forms.
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516
0. G014D0N HEWITT.
The cephalo-pharyngeal muscles (fig. 19).— These
muscles consist of four sets: (1) The cephalic retractor
muscles, which by their contraction draw the anterior end of
the larva and the pharyngeal mass inwards; (2) the pro-
tractor and depressor muscles of the pharyngeal mass;
(3) the muscles controlling the mandibular, dentate, and
hypostomal sclerites ; and (4) the internal pharyngeal muscles.
There are four chief pairs of cephalic retractor muscles, of
which the two ventral pairs are by far the largest. The
more ventral of these two pairs (v'. c.r.) arises on the ventral
side from the posterior end of the sixth segraeut, internal to
the ventrolateral, longitudinal muscles; the other pair
(v. c. r.), which is double, arises more laterally from the
posterior end of the fifth segment. The remaining pairs of
cephalic retractors arise from the posterior end of the third
segment. All the cephalic retractor muscles are inserted
anteriorly into a ring, the cephalic ring(c. r.), on the anterior
border of the second segment, the first post-oral segment.
There are two pairs of cephalo-pharyngeal protractor
muscles, a dorsal (d. c. p.) and a ventral pair (v. c. p.). Both
are rather broad fau-shaped muscles inserted by their broad
ends in the middle of the third segment, slightly to the sides
of the dorsal and ventral median lines respectively. The
dorsal and ventral muscles of each side are inserted together
on the dorso-lateral region of the posterior end of the
pharyngeal mass. The pair of depressor muscles (d. m.) which
are situated dorsally, are attached by their broader ends to the
intersegmental ring between segments three and four. They
are inserted on to the posterior end of the dorsal side of the
pharyngeal mass; by their contraction the posterior end of the
pharyngeal mass is raised, the result being that the sclerites
articulated to its anterior end are depressed.
There remain six pairs of muscles controlling the mandi-
bular, dentate and hypostomal sclerites, one pair controlling
the two foremost sclerites and four pairs controlling the hypo-
stomal sclerite. The mandibular extensor muscles (m. e.) are
attached to the body- wall in the third segment on each side
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STRUCTURE, DEVELOPMENT, AND BIONOJVUCS OP HOUSE-FLY. 517
of the median line and between the dorsal cephalo-pharyngeal
protractors. They are inserted on to the dorsal side of the
mandibular sclerite (m. s.) ; by their contraction they elevate
the sclerite. This sclerite is depressed by the contraction of
a pair of muscles which control the dentate sclerites (d. s.),
the latter fitting into a notch on the ventral side of the mandi-
bular sclerite. The mandibular depressor muscle (m. d.) is
attached to the posterior ventral pi'ocess of the lateral
pharyngeal sclerite by the three bands into which the posterior
portion of the muscle is divided; the anterior and single end
of the muscle is inserted on the ventral process of the dentate
sclerite. Four pairs of muscles (s. d.) are inserted on the
hypostomal sclerite (h. s.). Two more dorsal pairs are
attached to the intersegmental ring between segments three
and four as shown in fig. 16. The two more ventral pairs are
attached to the lateral pharyngeal sclerites, one being attached
to the ventral side of the posterior dorsal process and the
other to the ventral process beneath the mandibular depressor.
These muscles, which I call the stomal dilators, are inserted
on the sides of the hypostomal sclerite. Their function is, I
believe, to open and close the anterior pharyngeal aperture
and so control the flow of fluid food into the pharynx and of
the salivary secretion; the lowest pair of muscles may be more
directly concerned with the latter.
The pharyngeal apparatus is controlled, as in the adult fly,
by a series of muscles. In the larval stadium, however, where
so large an amount of food is required for the growth and
building up of the future insect, there is a greater development
and elaboration of the pharyngeal apparatus, including the
muscles. In the greater anterior region of the pharynx, that
is, the part lying within the pharyngeal sclerites (fig. 18), the
muscular system consists of two bands of oblique muscles
(o. ph.) arranged in pairs. The muscles are attached dorsally
to the inside dorsal edges of the lateral plates (I. p.) and
ventrally to the roof of the pharynx (r.ph.), the ventral attach-
ment being more posterior than the dorsal. The posterior
region of the pharynx, which is between the lateral plates and
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518
C. GORDON II E WITT.
the oesophagus (fig. 17), is controlled by two sets of muscles.
Two pairs of elongate oblique muscles (e. o. m.) are attached
dorsally to the dorsal edges of the lateral plates {I. p.) and
inserted ventrally on to the roof of the pharynx ; these muscles
assist the previously described oblique pharyngeal muscles in
raising and depressing the roof of the pharynx. They are
assisted in enlai'ging and contracting the lumen of the pos-
terior part of the pharynx by a number of semi-circular dorsal
muscles (s. d. m.), which by their contraction make the floor of
the pharynx more concave, and it is these muscles, I believe,
that are chiefly concerned in the maintenance of the peri-
staltic contractions of the pharynx, by means of which the
fluid food, which has been sucked into the mouth by the
pumping action of the pharynx, is carried on to the
oesophagus.
The similarity between the pharyngeal apparatus of the fly,
that is, of the fulcrum and that of the larva, is very striking,
both with regard to the form of the skeletal structures and
the musculature. If the pharynx of the larva were regarded
as being homologous to that of the fly it would further support
the view that the head of the larva had been permanently with-
drawn into the succeeding anterior body-segments. These
structures, however, may be merely analogous ; the similarity
of structure may have been brought about by similarity of
function. Both larva and adult subsist on fluids which are
sucked into the mouth and pumped into the oesophagus.
The series of muscular actions which takes place during
locomotion appears to be as follows. By the contraction of
the pharyngeal protractors the anterior end of the larva is
extended, the mandibular 'sclerite being extended at the
same time by the contraction of the mandibular extensor
muscles. The mandibular sclerite is now depressed by the
contraction of the mandibular depressors, and anchors the
anterior end of the larva to the substance through which it
is moving. A series of segmental linear contractions now
takes place, initiated by the large cephalic retractor muscles,
and carried on posteriorly from segment to segment by the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 510
dorso-lateral oblique, the internal lateral oblique, the longi-
tudinal ventro-lateral, the ventro-lateral oblique and ventral
oblique muscles. Each segment as it comes forward takos a
firm grip ventrally by means of the spiniferous pad. By the
time the last spiniferous pad has become stationary the
mandibular sclerite has left its anchorage, and by the con-
traction of the lateral and intersegmental muscles, which
takes place from before backwards, the lengths of the
segments of the larva are increased serially and the anterior
end begins to move forward again, when the whole process
is repeated.
3. Nervous System.
The central nervous system of the larva (PI. 82, fig. 23)
has attained what would appear to be the limit of ganglionic
concentration and fusion. The boat-shaped ganglionic mass,
which lies partly in the fifth segment, but the greater portion
in the sixth segment, is a compound ganglion and represents
the fusion of eleven pairs of ganglia similar to that which
Leuckart (1858) describes in the first larval stage of Melo-
phagus ovinus, but which, however, has not undergone so
great a degree of concentration as in M. domestica. This
ganglionic mass, which for convenience and brevity I shall
call the ganglion (Lowne's " neuroblast ") does not exhibit
externally any signs of segmentation, the interstices between
the component ganglia being filled up with the cortical tissue,
whose outer wall forms a plain surface. In horizontal and
sagittal sections, however, the component ganglia can be
recognised and their limits are "more clearly defined. The
ganglion is surrounded by a thick ganglionic capsular sheath
which is richly supplied with tracheas, and appears to be con-
tinuous with the outer sheath of the peripheral nerves. Two
pairs of large tracheal (fig. 24) ai'e found entering the gang-
lionic sheath, an anterior pair (tr. ') which runs in between
the cerebral lobes, and a lateral pair (tr. ") entering the gan-
glion beneath these lobes. In the young larva the cortical
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520
C. GOllDON HEWITT.
layer of cells is proportionately much thicker. The cortical
tissue is made up of cells of varying sizes, but which can be
grouped in two classes— smaller cortical cells and larger
ganglionic cells. Most of the ganglionic cells appear to be
unipolar, but there are many of a bipolar and multipolar
nature present ; they stain readily and possess fairly large
nuclei. These ganglionic cells are arranged segnientally, and
occur near the origin of the nerves. In the posterior region
of the ganglion, where the nerves arise in close proximity, the
ganglion cells are very numerous, relatively few of the cortical
cells being found. A further demarcation of the component
ganglia is brought about by median and vertical strands of
the ganglionic sheath-tissue, which perforate the compound
ganglion and occur as vertical strands along its median line.
Tracheae also penetrate the ganglion with these strands of
capsular tissue.
On the dorsal side of the anterior end of the ganglion is
situated a pair of spherical structures (c. L), which may be
termed the " cerebral lobes." They are united in the median
line dorsal to the foramen traversed by the oesophagus (oe.).
These cerebral lobes are chiefly of an imaginal character, and
contain the fundaments of the supra-cesophageal ganglia and
also of the optic ganglia of the future fly (fig. 27). Each is
surrounded by a thin membranous sheath (sh.) and is con-
nected with the major cephalic imaginal discs by the optic
stalk (o. 6'.).
The nerves arising from the ganglion may be divided into
three groups, according to their origin. Eleven pairs of
nerves (fig. 24, 1-11) corresponding to the eleven pairs of
ganglia arise, two from the anterior end and nine from the
sides of the ganglion. Three pairs of nerves (a., b. and c.)
arise laterally from the stalks of the pro-thoracic and meso-
thoracic imaginal discs. In the median dorsal line of the
posterior half of the ganglion a single pair (d. a.') and two
median unpaired (d. a. " d. a. "') nerves have their origin ;
these are accessory nerves.
The first pair of the two anterior pairs of nerves runs
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 521
forward and innervates the posterior region of the pharyngeal
mass; the anterior region of the latter is supplied by the
second pair of nerves. These nerves also innervate the
anterior segments of the body. The first (a) of the three
pairs of nerves which arise from the stalks of the imaginal
discs runs to the anterior end supplying the protractor and
retractor muscles of the pharyngeal mass. The second (b)
of these three pairs of nerves innervates the muscles of the
body-wall of the third and fourth segments; the latter segment
is also innervated by the third (c) of the three pairs of nerves.
The succeeding nine pairs of lateral nerves are segmentally
distributed, and innervate the muscles of the body-wall of
segments five to thirteen. Each nerve bifurcates on reaching
the muscles, and these branches further subdivide into very
fine nerves.
The nerves, which arise dorsally, and which I have called
the accessory nerves, are interesting. The first pair (d. a.')
which arises about mid-way along the dorsal side of the
ganglion, accompanies the pair of nerves supplying the
seventh segment. The second (d. a."), which is an unpaired
nerve, bifurcates in the seventh segment, and the resulting
nerves proceed to the body-wall in association with the nerves
supplying the eighth segment. The third and posterior
dorsal accessory nerve (d.a.'") bifurcates in the seventh seg-
ment. Each of the resulting nerves undergoes a second
bifurcation; the dextral nerve, bifurcating in the eighth
segment, accompanies the nerves supplying the ninth seg-
ment; the sinistral nerve bifurcates between segments
eight and nine, and the resulting nerves proceed to the tenth
segment. None of the remaining lateral nerves appear to be
accompanied by an accessory nerve, of which there are four
pairs only. The ganglionic sheath is penetrated by trachea?,
some of which arise from the ganglion in association with the
nerves which they accompany to the body-wall. Two of
these tracheae are shown (fig. 24, t.). Similar fine trachea)
arise with the three posterior pairs of lateral nerves, and
on account of their similarity to accessory nerves I at first
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522
C. GORDON HEWITT.
mistook them for such, even when dissecting with a magnifi-
cation of sixty-five diameters, until my serial sections showed
their real nature. Without sections it is impossible to dis-
tinguish these fine unbranchiug tracheae from accessory
nerves. I have mentioned this fact as showing the necessity
of supplementing the one method by the other.
The visceral or stomatogastric nervous system
(PI. 31, fig. 20) consists of a small central ganglion (c. g.) lying
on the dorsal side of the oesophagus, immediately behind the
transverse commissure of the cerebral lobes from the bases of
which two fine nerves are given off to join a fine nerve from
the ganglion, which runs dorsally towards the anterior end of
the dorsal vessel." A fine nerve from the ganglion runs
forward on the dorsal side of the oesophagus towards the
pharynx. A posterior nerve (fig. 24, v.n.) runs from the
ganglion along the dorsal side of the oesophagus to the neck
of the proveutriculus, where it forms a small posterior
ganglion (fig. 20, pv. g.), from which fine nerve-fibres arise
and run over the anterior end of the proventriculus.
Sensory organs. — The only sensory organs which the
larva possesses are the two pairs of conical tubercles (fig. 9,
o. t.), which have been described already on the oral lobes.
In section each consists of an external transparent sheath of
the outer cuticular layer ; beneath this and surrounded by a
chitinous ring are the distal cuticularised extremities of a
number of elongate fusiform cells grouped together to form
a bulb. These are nerve-end cells and their proximal extre-
mities are continuous with nerve- fibres by means of which they
are connected to the ganglion. Both sensory organs of each
oral lobe are supplied by the same nerve from the second of
the two anterior nerves. Judging from their structure these
organs appear to be of an optical nature, and this is the usual
view which is held with regard to their function. They
would appear merely to distinguish light and darkness, which,
for such cryptophagous larva, is no doubt all that is necessary.
The negative heliotropism of the larva of the blow-fly has
been experimentally proved by Tioeb (1890), and my own
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STPJTCTUBE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 523
observations confirm the same for the larvas of M. domes-
tic a.
The hypodermal cells are well innervated and the body-wall
appears to be highly sensitive.
4. The Alimentary System.
The alimentary tract increases in length at each of the
larval ecdyses, and in the mature larva (PI. 33, fig. 29), its
length is several times greater than the length of the larva.
The great length of the alimentary tract of the larva com-
pared with that of the fly is probably accounted for by the
fact that a large digestive area is necessaiw for the rapid
building up of the tissues from fluid food which takes place
during the larval life. It is divisible into the same regions
as the alimentary tract of the mature insect, but it differs
from the latter in several respects ; these regions are parts
of the original stomodseal, mesenteric and proctodreal regions
of which the mesenteric is by far the longest in this larva.
The regions of the alimentary tract which are derived from
the stomodasmn and proctodasum are lined with chitin of
varying thickness which is attached during life to the epithe-
lial cells, but is shed when the larva undergoes ecdysis. The
mesenteron does not appear to be lined with chitin as it is in
some insects, in which cases the chitinous intima usually lies
loose in the lumen ; it is, however, in the larva of M.
domesti ca, usually lined with a lining of a mucous character.
The whole alimentary tract is covered by a muscular sheath
of varying thickness.
The mouth (fig. 6, m.) opens on the ventral side between
the oral lobes. The ventral and ventro-latoral sides of the
oral lobes are traversed by a series of small channels (fig. 14,
ch.), which are made more effective by the fact that one side
of the channel is raised and overhangs the other so as to
partially convert the channels into tubes rather comparable
to the pseudo-tracheae of the oral lobes of the fly, to which
they have a similar function : the liquid food runs along these
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524
0. GORDON HEWITT.
channels to the mouth. Distally many of the channels unite ;
the resulting channels all converge and run into the mouth.
The anterior border of the oral aperture is occupied by the
mandibular sclerite (m. s.), and the posterior border is bounded
by a lingual-like process (I.) that is bilobed at its anterior
extremity.
Cephalo-pharyngeal sclerites (PI. 30, fig. 4). — The
sclerites associated with the cephalo-pharyngeal region are
rather similar to those of the second larval instar; they are,
however, of a more solid and of a thicker character. Between
the oral lobes is seen the median uncinate mandibular
sclerite (m. s.). The homology of this sclerite is obscure.
Lowne regarded it as being the labrum ; some authors con-
sider that it represents the fused mandibles. As we know
at present so little of the comparative embryology of these
larvae it will be best to retain the name by which it is
generally known. The basal extremity of the mandibular
sclerite is broad, and at each side a dentate sclerite (d. s.) is
articulated by means of a notch in the side of the mandibular
sclerite, the function of which has been shown already in
describing the muscles. The mandibular sclerite articulates
posteriorly with the hypostomal sclerite (h. s.). This consists
of two irregularly-shaped lateral portions united by a ventral
bar of chitin ; it is anterior to this bar of chitin that the
salivary duct opens into the front of the pharynx. The
sides of the hypostomal sclerite articulate with two processes
on the anterior edge of the lateral pharyngeal sclerites (I. p.).
The lateral pharyngeal sclerites or plates i*ecall the shape of
the fulcrum of the adult fly. Each is wider posteriorly than
anteriorly, and the posterior end is deeply incised ; at the
base of this incision the nerves and tracheae which supply the
interior of the pharynx enter. The lateral sclerites vary in
thickness, as will be seen in the figures of the sections of the
pharynx. They are united dorsally at the anterior end by a
dorsal sclerite (d. p. s.), and ventrally they are continuous with
the floor of the pharynx.
The pharynx (PI. 3], figs. 17 and 18) in certain respects is
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STRUOTTJEE , DE VE LOPM ENT, AN D BIONOMICS OF HOUSE-FLY. 525
similar to that portion of the pharynx of the fly which lies in
the fulcrum. The whole length of the floor of the pharynx is
traversed by a series of eight grooves separated by bifurcating
ribs which are T-shaped in section (fig. 18, t. r.), and are called
the "Tribs" by Holmgren (1904); they form a series of
eight tubular grooves. Holmgren believes that they may
have been derived from a condition similar to that found in
the pharynx of the larva of Phalacrocera, where the floor
of the pharynx is traversed by a number of deep but closed
longitudinal fissures. These pharyngeal grooves probably
have a straining function, but they may also be of use in
allowing a certain amount of the salivary secretion to flow
backwards towards the oesophagus. The musculature and
action of the pharynx has been described. On the dorsal
side of the pharyngeal mass and attached laterally to the
layer of cells covering the lateral sclerites there is a loose
membrane (m.), whose function, I believe, is to accommodate
the blood contained in the pharyngeal sinus (ps.) when the
roof of the pharynx is raised. Posteriorly the floor of the
pharynx curves dorsally and opens into the oesophagus.
The oesophagus (fig. 29, ce.) is a muscular tube beginning
at the posterior end of the pharyngeal mass. It describes a
dorsal curve when the larva is contracted, and then runs in
a straight line through the oesophageal foramen between
the cerebral lobes of the ganglionic mass and dorsal to the
ganglion to the posterior region of the sixth larval segment,
where it terminates and opens into the proventriculus. It is
of a uniform width throughout and is lined by a layer of flat
epithelial cells (fig. 25, ce. ep.) whose internal faces are lined
by a chitinous sheath (ch. %.), which is thrown into a number
of folds. There is nothing of the nature of a ventral diver-
ticulum forming a crop such as Lowne describes in the larva
of the blow-fly.
The proventriculus (fig. 29, pv.) varies slightly in shape
according to the state of contraction of the alimentary tract;
in the normal condition it is cylindrically ovoid and its axis
is parallel with that of the body. As will be seen from the
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526
0. GORDON HEWITT.
figure (fig. 25), it is rather similar to the proventriculus of the
imago in general structure. The oesophageal epithelium
penetrates a central core which is composed of large clear
cells (c. c.) ; its lumen, being oesophageal, is lined with chitin.
This core is surrounded by an outer sheath, the cells (e. v.) of
which are continuous with those of the ventriculus. At the
junction of the central core with the outer sheath of cells
there is a ring of small more deeply-staining cells (i.e.).
This ring was regarded by Kowalevski (1887) as the rudi-
ment of the stomodasum of the nymph, but Lowne is of the
opinion that it develops in the nymph into the proventriculus
of the imago. I believe that it forms a portion, at least, of
the proventriculus of the imago, as it exhibits a very close
resemblance to the ring of cells in this region figured in the
section of the proventriculus of the imago (fig. 20 of Part I).
The mesenteron of the mature larva is of very great
length, and is not divisible into the two regions of
ventriculus and small proximal intestine as in the imago, but
appears to have the same chai'acter throughout; hence Lowne
calls it the " chyle-stomach/' which term, or ventriculus (fig.
29, v.), may be used to designate the whole region from the pro-
ventriculus to the point at which the malpighian tubes arise.
It is very much convoluted and twisted upon itself. The
course of the ventriculus is almost constant, and can be better
understood from the figure than from any detailed description.
At the anterior end four tubular ca3ca (c. v.) arise. Their
walls consist of large cells whose inner faces project into the
lumen of the glands ; these glands were not present in the
imago. The epithelium of the ventriculus (fig. 30) is com-
posed of large cells (e. v.), which project into the lumen of
the alimentary tract ; they possess large nuclei and the sides
of the cells facing the lumen have a distinct striated appear-
ance, which is absent in those epithelial cells covered with a
chitinous intima. This striated appearance may be related
in some way to the production of the mucous intima which
is generally present in the ventriculus, and which appears to
take the place of the loose chitinous intima or peritrophic
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 527
membrane which oocurs in this region in numerous insects,
and which has been studied in detail by Vignon (1901) and
others. Below the epithelial cells a number of small cells
(g. c.) are found, which may be either gland cells or young
epithelial cells. In addition to these cells small groups of
deeply-staiuing fusiform cells {%. c.) are found below the
epithelium. These, I believe, are embryonic cells from
which the mesenteron of the imago arises. The Malpighian
tubes arise in the tenth segment at the junction of the ven-
triculus and the intestine.
The intestine (fig. 29, int.) is narrower than the ventriculus
and runs forwards as far as the eighth segment, where it bends
below the visceral mass and runs posteriorly, to become dorsal
again behind the tenth segment, from whence it runs back-
wards, turning ventrally behind the visceral mass to become
the rectum. The epithelium is thrown into a number of folds
and is covered with a chitinous intima.
The rectum (r.) is very short and muscular, and the chitinous
intima is fairly thick and continuous with the outer cuticular
layer of the chitinous integument. It is almost vertical and
opens by the anus on the ventral side of the terminal larval
segment between the two swollen anal lobes.
Salivary glands. — There is a pair of large tubular
salivary glands (s.gl.) lying laterally in segments five and six.
Anteriorly each is continued as a tubular duct; the two ducts
approach each other and join beneath the pharyngeal mass to
form a single median duct (fig. 19, sal. d.) which runs forward
and opens into the pharynx on the ventral side as already
described. The glands are composed of large cells (fig. 21),
which project into the lumen of the gland ; they stain deeply
and have large active nuclei. The salivary secretion, apart
from the digestive properties which it has, is no doubt of
great importance in making the food more liquid, as is also
the case in the imago, and so rendering it more easy for
absorption.
The Malpighian tubes (fig. 29, m. t.) arise at the junction of
the ventriculus and intestine in the tenth segment. A short
vol. 52, part 4. 40
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528
0. GORDON HEWITT.
distance from their origin they bifurcate and the resulting
four tubules have a convoluted course, being mingled to a
great extent with the adipose tissue. They are similar in
appearance and histologically to those of the imago, consisting
of large cells, of which only two can be seen usually in section ;
they consequently give the tubules a moniliform appearance.
In the mature larva these cells appear to break down to form
small deeply-staining spherical bodies. This histological
degeneration begins at the distal ends of the tubules, which in
the mature larva usually have the appearance shown in fig. 28
(m. t.) ; all the stages of degeneration can be traced out.
This process may be a means of getting rid of the remaining
larval excretory products.
The four caeca at the anterior end of the ventriculus have
already been described.
5. The Bespiratory System.
The tracheal system (fig. 26) of the adult larva consists of
two longitudinal tracheal trunks united by anterior and
posterior commissures, and communicating with the exterior
by anterior and posterior spiracles, the latter are situated in
the middle of the oblique caudal end, and the anterior spiracles,
which are not present in the first larval instar, are situated
laterally at the posterior border of the third body-segment.
I believe that the anterior spiracles (a. sp.) are true func-
tional spiracles, though for some time I shared Lowne's
opinion that they were not functional. This latter view was
due to the fact that it was difficult to understand how these
spiracles could obtain air when they are immersed, as they
usually are, in the moist fermenting materials on which the
animal feeds. A careful examination of their structure, how-
ever, strengthens my belief that they are able, if necessary,
to take in air; the occasions when this is possible are
probably not infrequent. Each of the anterior spiracular
processes consists of a fan-shaped body (fig. 9, a. sp.) bearing
six to eight small papilliform processes. The papillas (fig. 7)
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 529
open to the exterior by a small pore which leads into a cavity
haviug a clear lumen surrounded by branched cuticular pro-
cesses, whose fuuction is probably to prevent solid particles
from penetrating the spiracular channel. The body of the
fan-shaped spiracular process is filled with a fine reticulum of
the chitinous intiuia, which Meijere (1902) calls the " felted-
chamber " (Filzkammer) ; through this meshwork the air can
pass to the longitudinal tracheal trunk.
The posterior spiracles (fig. 3, p.sp.) are D-shaped with the
corners rounded off aud their flat faces are opposed. Each
consists of a chitiuous ring having internal to the flat side a
small pierced knob. Each chitinous ring encloses three
sinuous slits, guarded by inwardly-directed fine dendritic
processes; through these slits the air enters the small
spiracular atrium, one of which is situated internal to each of
the spiracles. The spiracular atria communicate directly with
the longitudinal tracheal trunks.
The course and origin of the branches of each of the
longitudinal tracheal trunks (n'g. 26 I. tr.) is the same, so that
of the left side will be described only. Immediately behind
the spiracular atria the short posterior tracheal commissure
(p. com.) connects the two trunks. In the younger larvse this
commissure is situated more anteriorly, but in the adult it is
situated so far back and so close to the spiracles that its
presence might easily be overlooked. On the outer side of the
tracheal trunk a large branch arises ; this, the visceral branch
(v. tr.), bends ventrally to the lateral trunk, and thus becoming
internal to it enters the convoluted visceral mass with its
fellow of the other side. The visceral branches extend
anteriorly as far as the seventh segment. In the twelfth and
thirteenth segments the lateral tracheal trunk has a double
appearance. A dorsal and a ventral branch arise in most of
the segments, the dorsal branch chiefly supplies the fat body,-
and the ventral branch supplies the viscera; both give off
branches to the muscular body wall. The anterior commissure
(a. com.) is situated in the fourth segment. It crosses the
oesophagus immediately behind the pharyngeal mass. On
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0. GORDON HEWITT.
the internal side of the portion of the lateral tracheal trunk
that is anterior to the commissure a branch arises, and running
ventral to the pharyngeal mass it supplies the anterior end of
the larva and the oral lobes. A branch that supplies the
muscles of this region is given off external to the origin of the
anterior commissure. Internal to the origin of the commissure
two tracheae arise; the anterior branch enters and supplies the
pharyngeal mass, and the posterior brauch (tr/) enters the
ganglion ventral to the cerebral lobes. In the fifth segment
another internal tracheal branch enters the ganglion {tr.").
These tracheae which supply the ganglion appear to run
chiefly in the peripheral regions, where they divide into a
number of branches, the fate of some of these being interesting.
These branches are extremely fine, and they arise, as I have
previously mentioned, in association with a number of the
segmental nerves with which they run to the body wall.
6. The Vascular System and Body Cavity.
The relations and structure of the vascular system of the
larva are on the whole similar to those of the fly ; there are,
however, a number of inodifications.
The dorsal vessel, which includes the so-called " heart," is
a simple muscular tube lying on the dorsal side immediately
beneath the skin, and extending from the posterior tracheal
commissure to the level of the cerebral lobes of the compound
ganglion in the fifth segment. Its wall is composed of fine
striated muscle-fibres arranged transversly and longitudinally,
but chiefly in the latter direction. The swollen posterior
region (PL 33, fig. 31), which is called the heart, lies in the
last three or four segments, its anterior limit being hard to
define. It consists of three distinguishable chambers, which,
however, are not divided by septa. Three pairs of ostia (os.),
each provided with a pair of internal valves (v.), are situated
laterally, and place the cardiac cavity in communication with
the pericardium, in which this portion of the dorsal vessel
lies. There are three pairs of alar muscles controlling the
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STUUOTU.UE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 531
action of this posterior cardiac region of the dorsal vessel.
Lowne describes other openings in the wall of the "heart"
of the blow-fly larva, but I have been unable to find others
than those already described in this larva ; it has three pairs
only.
The dorsal aorta is the anterior continuation of the dorsal
vessel, which gradually diminishes in diameter. When it
reaches the fifth segment and lies above the ganglion, it ter-
minates in a peculiar cellular structure (fig. 24, c.r.), which
in the blow-fly has a circular shape and was called by
Weismann the "ring." In the larva of M. domes tica it
has not so pronounced a ring-like appearance, but is more
elliptically compressed and rather A-shaped. The cells of
which it is composed have a very characteristic appearance,
and are rather similar to a small group of cells lying on the
neck of the proventriculus and at the anterior end of the
dorsal vessel of the fly. From the lower sides of this cellular
structure (fig. 28, c. r.) the outer sheaths of the major cephalic
imaginal discs depend, and extend anteriorly to the pharyngeal
mass, enclosing between them the anterior portion of the great
ventral blood sinus.
The pericardium lies in the four posterior segments of the
body, and is delimited ventrally from the general body-cavity
by a double row of large characteristic pericardial cells. These
cells have a fine homogeneous structure and are readily dis-
tinguished from the adjacent adipose tissue cells, Avhose size
they do not attain. The pericardial cavity contains a profuse
supply of fine tracheal vessels which indicates a respiratory
function. A similar condition occurs in the blow-fly larva, and
Imms (1907) has described a rich pericardial tracheal supply
in the larva Anopheles maculipenuis, as also Vaney (1902)
and Dell (1905) in the larva of Psychoda punctata. The
adipose tissue cells (fig. 28,/. c.) form the very prominent
" fat-body." They are arranged in folded cellular laminse
that lie chiefly in the dorso-lateral regions of the body, and in
section have the appearance shown in the figure. The cells
have a similar structure to those of the adult fly; they are
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532
C. GORDON HEWITT.
very large, with reticular protoplasm containing fat globules,
and tliere may be more than one nucleus in a single cell. As
in the fly, the fat-body is closely connected with the tracheal
system by means of a very rich supply of trachea?.
Two chief blood-sinuses can be distinguished — the peri-
cardial sinus, which has already been described, lying in the
dorsal region in the four posterior segments, and the great
ventral sinus. The latter lies between the outer sheaths of
the major cephalic imagiual discs and extends anteriorly into
and about the pharynx ; posteriorly it encloses the ganglion
and the convoluted visceral mass, above which it opens into
the pericardial sinus between the pericardial cells.
The blood which fills the heart and sinuses and so bathes
the organs is an almost colourless, quickly coagulable fluid,
containing colourless, nucleated, amoeboid corpuscles and small
globules of a fatty character.
7. The Imaginal Discs.
As in other cyclorrhaphic Diptera, the imaginal discs of
some of which have been described by Weismann (1864),
Kunckel d'Herculais (1875-78) and Lowne, the imago is
developed from the larva by means of these imaginal rudi-
ments, which are gradually formed during the later portion of
the larval life. They do not all appear at the same time, for
whereas some may be in a well-developed state early in the
third larval instar, others do not appear until the larva
reaches its resting period or even later. The imaginal discs
appear to be hypodermal imaginations though their origin is
difficult to trace in all cases; in many instances they are con-
nected with the hypodermis by means of a stalk of varyiugthick-
ness. The imaginal disc or rudiment may consist of a simple
or of a folded lamina of deeply-staining columnar embryonic
cells, as in the wing discs, or of a number of concentric rings
of these cells, as in the antennal and crural discs. They are
usually closely connected with the trachea? and in some cases
arc iunervated by fine nerves. Although the imagiual discs
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 533
of M. doinestica are similar in some respects to those of the
blow-fly, as described by Lovvne, there are several important
differences, chief of which is the position of the imaginal discs
of the meta-thoracic legs.
During the resting period of the larva the cephalic and
thoracic discs can be distinguished, but the abdominal discs
arc small and not so obvious except in sections.
The cephalic discs. — The chief cephalic discs are con-
tained in what at first appears to be a pair of cone-shaped
structures in front of each of the cerebral lobes of the gan-
glion (fig. 24, m.c.d.) ; the cone, however, is not complete.
The outer sheath of each of these major cephalic imaginal
rudiments is continued dorsally, aud joins the cellular struc-
ture mentioned previously (see fig. 28), thus enclosing a
triangular space which is a portion of the venti'al sinus.
These sheaths are continued anteriorly and are connected to
the pharyngeal mass, and it is through this connecting strand
of tissue that the discs are everted to form the greater part
of the head of the nymph. Immediately in front of the
cerebral lobe is the so-called optic disc (fig. 27, o. d.), which
in its earlier stages is cup-shaped, but later it assumes a
conical form, having a cup-shaped base adjacent to the cere-'
bral lobe. The optic disc is connected to the cerebral lobe
laterally by a stalk of tissue, the optic stalk (o.s.), Avhich
becomes hollow later, and it is through this stalk that the
optic ganglion and associated structures contained in the
cerebral lobe appear to evaginate when the final metamorphosis
and eversion of the imaginal rudiments takes place. The optic
discs form the whole of the lateral regions of the head of the
fly. The remaining portion of the head-capsule of the fly is
formed from two other pairs of imaginal rudiments, the
antennal and facial discs. The antennal disc (an. d.) lies in
front of, and internal to, the optic discs. Each consists of an
elongate conical structure, in which at a later stage the
individual antennal joints can be distinguished. The facial
discs (f.d.) are anterior to the antennal discs and extend to
the anterior end of the conical structure containing these
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534
0. (I0RD0N H 15 WITT.
three pairs of major cephalic discs, which will form the
cephalic capsule.
In addition to these two other pairs of cephalic discs are
found. A pair of small flask-shaped maxillary rudiments are
situated one at the base of each of the oral lobes; a second
pair of imaginal discs, similar in shape to the maxillary discs,
is found adjacent to the hypostomal sclerite ; the latter, I
believe, are the labial rudiments, and will form almost the
whole of the proboscis of the fly.
The thoracic discs. — In M. domestica there are five
pairs of thoracic discs. The pro-thoracic imaginal discs (figs-
24 and 28, pr. d.) are attached to the anterior end of the gan-
glion and slope obliquely forwards; the distal end of each is
attached to the body-wall on the ventral side between seg-
ments three and four. These discs develop into the pro-
thoracic legs, and probably also into the much reduced
pro-thoracic segment, as I was unable to discover any other
rudiments corresponding to the dorsal imaginal discs of the
meso-thoracic and meta-thoracic segments. Arising from the
sides of the ganglion immediately behind the attachment of
the pro-thoracic rudiment are the imaginal rudiments of the
meso-thoracic legs and sternal region (v. ms.) ; the distal stalks
of this pair of imaginal discs are attached to the body-wall at
the posterior border of the fourth segment. The dorsal meso-
thoracic imaginal discs, from which originate the mesonotal
region and the wings, may be termed the alar or wing discs.
They form a pair of flattened pyriform saca (fig. 22, d.ms.),
lying one on each side of the ventral side of the fifth segment
and slightly external to the lateral tracheal trunk (fig. 28,
d.ms.), to a ventral branch of which each is attached. The
meta-thoracic discs consist of two pairs of small pyriform
masses (fig. 22) lying immediately behind the alar discs in
the intersegmental line. They are attached to a ventral
branch of the lateral tracheal trunk. The anterior rudiment
(v. mt.) is the larger, and forms the imaginal meta-thoracic leg
and sternal region ; in the blow-fly and Volucella it is interest-
ing to note that this pair of imaginal discs is situated further
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 535
forward, and is in association' with the corresponding pro-
thoracic and meso-thoracic ventral discs. The smaller and
more posterior disc (d. mt.) will develop into the remaining
portion of the much reduced meta-thoracic segment, including
the halteres.
Eeference has already been made to other imaginal rudi-
ments which occur in the abdominal region as circular patches
of embryonic cells. The abdominal segments develop from
numerous segmentally arranged plates of a similar nature;
which are found during the early pupal stage.
During pupation the imaginal rudiments increase in size
and are not destroyed by the phagocytes in histolysis, as is
the case with most of the larval structures. The cephalic
discs are evaginated by the eversion of their sacs by way of
the anterior end of the larva, a cord of cells attached to the
dorsal wall of the anterior end of the pharynx marking the
path of eversion. A similar process takes place in the case
of the thoracic imaginal discs, which, by their eversion, build
up the whole of the skeletal case of the thorax and its dorsal
and ventral appendages, the wings, halteres and legs.
VI. Summary.
1. An account of the previous work on the breeding habits
ofM. domesticais given, which, together with the author's
investigations, show that the house-fly breeds in the following
substances :
Horse-manure; this is preferred by the female flies as a
nidus for the eggs, and forms the chief substance in which
they breed ; human excrement, either in the form of isolated
faeces or occurring in such places as latrines, privies and ash-
pits; cow-dung; poultry excrement ; also in substances con-
taminated or mixed with excremental products, such as
bedding from piggeries and from rabbits and guinea-pigs,
paper and textile fabrics which have been contaminated, as
cotton and woollen garments, sacking, rotten flock-beds,
straw-mattresses, cesspools ; decaying vegetable substances
vol. 52, part 4. 41
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536
0. GORDON HEWITT.
such as vegetable refuse from kitchens and decaying grain ;
rotten fruit, as bananas, apricots, cherries, plums, peaches and
melon-slices ; in spent hops ; in waste food-stuffs, as bread
moistened with milk, boiled egg, broth; bad meat and dead
animals.
2. The most important factor in the development is tem-
perature; a hig-h temperature accelerates the development.
Others factors concerned in the development are — the nature
of the food and moisture, the effects of which are shown.
Fermentation is also an important factor in development, as
first shown by de Greer.
3. The shortest time occupied in the development, that is,
from the deposition of the egg to the exclusion of the imago,
is eight days, which period is obtained when the larva? are
incubated at a constant temperature of about 35° C. ; under
unfavourable conditions the development may extend over
several weeks.
4. There are three larval stages, aud the shortest times
obtained for the development of the different developmental
stages is — egg, from deposition to hatching, eight hours ;
first larval instar, twenty hours; second larval instar, twenty-
four hours ; third larval instar, three days ; pupal stage,
three days.
5. House-flies usually breed from June to October, but if
the necessai'y conditions of temperature and suitable food are
present they are able to breed practically the whole year
round ; these conditions are not, as a rule, satisfied during
the winter months, except in such places as warm stables, etc.
6. The flies become sexually mature in ten to fourteen days
after their emergence from the pupa, and hey may begin to
deposit their eggs as early as the fourteenth day after
emergence. Each fly lays from 120-150 eggs in a single
batch, and it may lay as many as six batches during its life.
7. The anatomy of the adult larva is described in the
second portion of the paper. The body of the larva is con-
sidered to be composed of thirteen segments, of which the
remnant of the cephalic region or pseudo-cephalon forms the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 537
first. The apparent single second segment is considered to
be of a double nature.
8. The muscular system is described in detail. It consists
of: (1) A segmentally-arranged series of flattened cutaneous
muscles forming an almost perfect sheath below the hypo-
dermis ; (2) the muscles controlling the cephalo-pliaryngeal
sclerites and pharynx; (3) the cardiac and visceral muscles.
The series of muscular actions which probably takes place
during locomotion is described.
9. The central nervous system is concentrated to form a
single compound ganglion in which eleven pairs of compo-
nent ganglia can be recognised. On the dorsal side of the
anterior end of the ganglion two cerebral lobes united in the
median line above the oesophageal foramen are situated;
these contain the rudiments of the optic and snpra-cesophageal
ganglionic structures of the fly. Eleven pairs of segmental
nerves arise from the ganglion, and in addition to these three
pairs of lateral nerves, and also a single pair and two median
unpaired dorsal accessory nerves arise. The component
ganglia are surrounded by a cortical layer containing large
ganglion cells ; the whole compound ganglion is enclosed in a
capsular sheath.
The only sensory organs are two pairs of tubercles situated
on the dorsal sides of the oral lobes. By their structure they
indicate an optical function.
10. The alimentary tract is very long in the larva, the
ventriculus being especially elongate. It consists of pharynx,
oesophagus, proventriculus, ventriculus, intestine and rectum.
In addition to a pair of salivary glands, whose ducts unite to
open by a single duct at the anterior end of the pharynx, and
a pair of bifurcating Malpighan tubes, the larva possesses four
caeca at the anterior end of the ventriculus. The ventri-
culus and intestine are very convoluted and are coiled up to
form a complicated visceral mass.
11. The tracheal system of the adult larva consists of two
longitudinal lateral tracheal trunks united hj anterior and
posterior commissures, and communicating with an exterior
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538 0. GORDON HEWITT.
by means of an anterior and a posterior pair of spiracles.
The anterior spiracles, which do not occur in the first larval
instar, are considered to be functional.
12. The vascular system consists of : (1) A dorsal vessel,
the posterior region of which is swollen to form a cardiac
region or "heart" which communicates with a pericardial
cavity by means of three pairs of lateral ostia ; (2) the great
ventral sinus, which forms the body cavity ; and (3) the peri-
cardial sinus. The pericardium is well supplied with tracheae,
which may assist in respiration, as in certain other insect
larvae. The adipose tissue cells which compose the large
laminee forming the fat-body are similar in structure to those
of the fly.
13. Three groups of imaginal rudiments or discs can be
recognised in the larva : (1) The cephalic discs, of which two
appendicular pairs are situated at the anterior end of the larva
and three pairs in front of the cerebral lobes of the ganglion ;
(2) the thoracic discs, two pairs of which are attached to the
anterior end of the ventral side of the ganglion, and three
pairs are connected with the lateral tracheal trunks in the fifth
segment ; (3) the abdominal and visceral discs.
VII. Literature.
For the sake of convenience a few of the references given
in Part I have been repeated here.
1902. Berlese, A.— " L'accoppiamento della Mosca domestica," 'Rev.
Patalog. vegetale,' vol. ix, pp. 345—357, 12 figs.
1834. Bouche, P. Fa.— 'Naturgeschichte der Insekten besonders in hinsiclit
ihrer ersten Zustande als Larven und Puppen,' Berlin, 216 pp.,
10 pis. (M. domestica, pp. 65, 66, pi. v, figs. 20—24.)
1883. Brauer, F— "Die Zweifluger des kaiserlichen Museums zu Wien :
III. Systematische Studien auf Grundlage der Dipteren larven nebst
einer Zusammenstellung von Beispielen aus Literatur iiber dieselben
und Beschreibung neur Pormen," ' Denksohr. der Kais. Akad. der
Wiss. math-naturwiss. Classe,' Wien, vol. xlvii, pp. 1—100, 5 pis.
(99)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 539
1905. Dell, J. A. — "On the Structure and Life-history of Psychoda sex-
punctata," 'Trans. Ent. Soc. London,' pp. 293—311.
1776. de Geek, Carl. — 'Memoires pour servir a l'Histoire des Insectes,'
Stockholm. (M. domestica, vol. vi, pp. 71 — 78, pi. iv, figs. 1 — 11.)
1908. Griffith, A.— "The Life-history of House-flies," 'Public Health,'
vol. xxi, pp. 122—127.
1901. Henneguy, L. F. — 'Les Insectes,' Paris, 804 pp.
1906. Hewitt, C. G. — "A Preliminary Account of the Life-history of the
Common House-fly (Musca domestica, L.)," ' Manchester Mem.,'
vol. li, part i, 4 pp.
1907. ■ "The Structure, Development, and Bionomics of the House-fly,
Musca domestica, Linn.: Part I. The Anatomy of the Ply,"
'Quart. Journ. Micr. Sci.,' vol. 51, pp. 395—448, pis. 22—26.
1901. Holmgren, N. — "Zur Morphologie des Insektenkopfes : II. Einiges
iiber die Reduktion des Kopfes der Diptereu-larven," ' Zool. Ann.,'
vol. xxvii, pp. 343 — 355, 12 figs.
1896—1906. Howard, L. 0.—" House-flies," in ' The Principal Household
Insects of the United States,5 by L. O. Howard and C. L. Marlatt,
U.S. Dept. of Agriculture, Washington, Division of Entomology,
Bull. No. 4, N.S., revised ed., pp. 43—47, and figs. 13—15 ; and
1906, " House-flies," revised ed., Circular No. 71, 10 pp., 9 figs.
1900. "A Contribution to the Study of the Insect Fauna of Human
Excrement (with especial reference to the spread of Typhoid Fever
by Flies)," 'Proc. Wash. Acad. Sciences,' vol. ii, pp. 541—604,
figs. 17—38, pis. 30, 31.
1907. Imms, A. D,— "On the Larval and Pupal Stages of Anopheles
maculipennis, Meigen," 'Journ. of Hygiene,' vol. vii, pp. 291—
318, 1 fig., pis. 4, 5.
1790. Keller, J. C— ' Geschichte der gemeinen Stubenfliege,' Nurnberg,
32 pp., 4 pis.
1887. Kowalevski, A. — "Beitrage zur Kenntniss der nachembryonalen
Entwicklung der Musciden," 'Zeit. f. wiss. Zool.,' vol. xlv, pp.
542—594, pis. 26—30.
1875-81. Kunckel d'Herculais, J.—' Recherches sur l'organisation et le
Developpement des Volucelles, Insectes dipteres de la famille des
Syrphides,' Paris, part i.
1858. Leuckart, R.— "Die Fortpflanzug und Entwicklung der Pupiparen.
Nach Beobachtungen an Melophagus ovinus," ' Abhandl. Naturf-
Geseli.,' Halle, vol. iv, pp. 147—226, 3 pis.
VOL. 52, PART 4. NEW SERIES. 42
(100)
540
C. GORDON HEWITT.
1890. Loeb, J. — ' Der Heliotropismus der Thiere und seine Uebereinstim-
mung mit dem Heliotropismus der Pflanzen,' Wurzburg, 118 pp.,
6 figs.
1890-92. Lowne, B. T. — * The Anatomy, Physiology, Morphology, and
Development of the Blow-fly (Calliphora erythrocephala),'
vol. i, London.
1762. Lyonet, P. — ' Traite anatomique de la Chenille qui ronge le bois de
Saule,' 2nd ed., La Haye, 18 pis.
1902. de Meijere, J. C. H— " Ueber die Prothorakalstigmen der Dipteren-
puppen," 'Zool. Jahrb.' (Anat.), vol. xv, pp. 623—692, pis. 32—35.
1839. Newport, G.— " Insecta," in Todd's 'Cyclopaedia of Anatomy and
Physiology,' vol. ii, pp. 853 — 994.
1907. Newstead, R.— 'Preliminary Report on the Habits, Life-cycle, and
Breeding Places of the Common House-fly (Musca domestica,
Lin.) as observed in the City of Liverpool, with suggestions as to
the best means of checking its increase,' Liverpool, 23 pp., 14 figs.
1874. Packard, A. S. — "On the Transformations of the Common House-fly,
with notes on allied forms," ' Proc. Boston Soc. Nat. Hist.,' vol. xvi,
pp. 136—150, 1 pi.
1738. Reaumur, R. A. F. de. — 'Memoires pour servir a l'Histoire des In-
sectes,' vol. 4. (M. domestica, p. 384.)
1862. Schiner, J. R. — 'Fauna Austriaca: Die Fliegen,' Wien., vol. i,
674 pp.
1907. Smith, F. — "House-flies and their ways at Benares,' * Journ. Roy.
Army Med. Corps,' vol. ix, pp. 150 — 155 and p. 447.
1880. Taschenberg, E. L. — 'Praktische Insektenkunde,' part iv (M. do-
mestica, pp. 102—107, fig. 27).
1902. Vaney, C. — "Contributions a l'etude des Larves et des metamor-
phoses des Dip teres," 'Ann. de l'Univ. de Lyon,' N.S., I. Sciences-
med., fasc. 9, 178 pp., 4 pis.
1901. Vignon, P. — "Recherches de Cytologie generale sur les Epitheliums,
l'appareil parietal protecteur ou moteur; le role de la co-ordination
biologique," 'Arch. Zool. Exp. et Gen.,' vol. ix, pp. 371—720, pis.
xv — xviii.
1863. Weismann, A.—" Die Entwickelung der Dipteren im Ei, nach Beobach-
tungen an Chironomus spec, Musca vomitoria und Pulex
canis," * Zeit. f. wiss. Zool.,' vol. xiii, pp. 107—220, pis. vii— xiii.
1864. "Die nachembryonalen Entwickelung der Muscidcn nach
Beobachtungen an Musca vomitoria und Sarcophaga car-
naria," 'Zeit. f. wiss, Zool.,' vol. xiv, pp. 185— 336, pis. xxi— xxvii.
The University,
Manchester.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOTJSE-FLY. 541
EXPLANATION OF PLATES 30—33,
Illustrating Mr. C. Gordon Hewitt's paper on "The Structure,
Development, and Bionomics of the House-fly Musca
domestica, Linn. Part II. The Breeding Habits
Development and the Anatomy of the Larva."
PLATE 30.
Fig. 1. — Eggs of M. domestica, x 40, dorsal and dorso-lateral views.
a. Anterior end.
Eig. 2. — Egg immediately before emergence of the larva which can be seen
through the dorsal split of the chorion through which it emerges.
Eig. 3. — Posterior end of mature larva (3rd instar).
an. Anus. p.sp. Posterior spiracle.
Eig. 4. — Cephalopharyngeal skeleton of mature larva, left lateral aspect.
d.p.s. Dorsal pharyngeal sclerite. d.s. Dentate sclerite, h.s. Hypostomal
sclerite. l.p. Lateral pharyngeal sclerite or plate, deeply incised posteriorly
to form dorsal and ventral processes, m.s. Mandibular sclerite.
Eig. 5. — Mature larva of M. domestica.
a.sp. Anterior spiracular process, an.l. Anal lobe. sp. Spiniferous pad.
I-XIII. Body segments.
Fig. 6. — Ventral aspect of the Pseudocephalon and second body segment
of the mature larva showing the two oral lobes traversed by the food channels.
I. Lingual-like process, m. Mouth, m.s. Mandibular sclerite. o.t. Ante-
rior optic tubercle.
Fig. 7. — Transverse section through two of the papilla; of the anterior
spiracular process to show the clear central lumen.
c.p. The cuticular processes.
Eig. 8. — Larva shortly after hatching (1st instar).
m.s. Mandibular sclerite. p.sp. Posterior spiracle raised on short tubercle.
sp. Spiniferous pad.
Eig. 9.— Lateral (left) aspect of the anterior end of the mature larva.
I-1V. Body segments, a.sp. Anterior spiracular process showing seven
spiracular papilla;, m.s. Mandibular sclerite. o.t. Optic tubercle, ps. Pseudo-
cephalon.
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542
C. GORDON HEWITT.
Fig. 10.— "Nymph" of M. domestica dissected out of pupal case about
30 hours after pupation.
an. Swellings of nymphal sheath marking bases of antennse. ex. Coxa of
leg. lb. Labial portion of proboscis sheath. Ibr. Labral portion of same.
n.sp. Spiracular process of nymph, w. Wing in nymphal alar sheath.
Fig. 11.— Head of "nymph" (about 48 hours after pupation). Enclosed
in nymphal sheath. To show the development of the imaginal proboscis.
an. Antenna, c.e. Compound eye. fac. Facialia. lab. Labrum. mx.p.
Maxillary palp. o.l. Oral lobe.
Fig. 12. — Posterior end of larva in the second stage (2nd instar).
an. Anus. p.sp. Posterior spiracle.
Fig. 13.— Cephalopharyngeal skeleton of the first larval instar; the out-
line of the pharyngeal mass is shown in dotted lines.
t.s. T-shaped sclerite of the left oral lobe. Other lettering as in Pig. 4.
Pig. 14.— Longitudinal section through the surface of one of the oral lobes
of mature larva to show the food-channels.
ch. Food-channel, ct. Outer layer of cuticular integument, ct' . Inner
layer of the same. hy. Hypodermis.
Fig. 15. — Pupal case of M. domestica from which the imago has emerged,
thus lifting off the anterior end or "cap" of the pupa; ventro-lateral aspect.
a.sp. Remains of the anterior spiracular process of larva, l.tr. Remains of
the larval lateral tracheal trunk, n.sp. Temporary spiracular process of
nymph, p.sp. Remains of the posterior spiracles of larva.
PLATE 31.
Fig. 16. — Muscular system of the body-wall of the right side. The straight
dorsal line is the median dorsal line of the body, and the curved ventral line
is the median ventral line.
I — XIII. Body segments, an.l. Anal lobe. an.m. Anal muscle, c.r.
Cephalic retractor muscle, d.v. Dorso-ventral muscle of the terminal seg-
ment, ex.d.l. External dorso-lateral oblique recti muscles, i.l.o. Internal
lateral oblique muscle, in.d.l. Internal dorso-lateral oblique recti muscles.
l.i.m. Lateral intersegmental muscle, l.m. Lateral muscles, l.tr. Branch of
lateral tracheal trunk communicating with the anterior spiracular process.
l.v.l. Longitudinal ventro-lateral muscles, p.sp. Posterior spiracle, s.d.
Stomal dilators, v.c.r., v'.c.r. Ventral cephalic retractor muscles, v.l.o.
Ventro-lateral oblique muscle, v.o. Ventral oblique muscle.
Fig. 17. — Oblique section through the pharyngeal mass of the larva in the
direction and at the level shown by the line a.b. in Fig. 19. (Camera lucida
drawing.)
e.o.m. Elongate oblique pharyngeal muscle, l.p. Lateral pharyng
pal
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 543
sclerite. m. Accommodating membrane, m.d. Mandibular depressor muscle.
o.ph. Oblique pharyngeal muscle, ph. Pharynx, s.d.m. Semicircular dorsal
pharyngeal muscles, tr. Trachea, v.c.p. Ventral cephalic protractor muscle.
Fig. 18. — Oblique section through the pharyngeal mass of the larva at the
level shown by the line x.y. in Fig. 19. (Camera lucida drawing.)
p.s. Pharyngeal sinus, r.ph. Roof of pharynx. T.r. T-ribs of the floor of
pharynx. Other lettering as in Figs. 17 and 19.
Fig. 19. — Muscles of the cephalo-pharyngeal sclerites of the mature larva
seen from the left side. The muscles of the body-wall have been omitted
with the exception of the large cephalic retractor muscles.
a.b., x.y. Levels and direction of the oblique sections shown in Figs. 18
and 19. c.r. Cephalic ring, d.c.p. Dorsal cephalic protractor muscle, d.m.
Right pharyngeal depressor muscle, d.s. Dentate sclerite. /.p. Chitinous
floor of the posterior region of the pharynx showing the bases of the T-ribs.
h.s. Hypostomal sclerite. m.d. Mandibular depressor muscle, m.e. Mandi-
bular extensor muscle. m.s. Mandibular sclerite. s.d. Stomal dilator
muscles, sal.d. Common salivary duct, v.c.p. Yentral cephalic protractor
muscles, v.c.r. and v' .c.r. Ventral cephalic retractor muscles.
Fig. 20. — Visceral or stomatogastric nervous system of the mature larva.
The position of the ganglion (G.) with the cerebral lobes (c.l.) is shown by
means of the dotted outline.
e.g. Central visceral ganglion, pv.g. Proventricular or posterior ganglion.
Fig. 21. — Transverse section of one of the salivary glands of the mature
larva. (Camera lucida drawing.)
Fig. 22. — Internal aspect of the posterior thoracic imaginal discs of the
right side.
d.ms. Dorsal mesothoracic or alar imaginal disc. d.mt. Dorsal meta-
thoracic imaginal disc. l.tr. Lateral tracheal trunk of the right side of larva.
v.mt. Ventral metathoracic imaginal disc.
PLATE 32.
Fig. 23.— Nervous system of the mature larva. The dorsal accessory
nerves are shown by single black lines, and the outline of the pharyngeal mass
is indicated by the dotted line.
I — XIII. Body segments of the larva, c.l. Cerebral lobes, m.c.d. Major
cephalic imaginal discs, as. (Esophagus, o.v. Anterior (oesophageal branch)
of visceral nervous system.
Fig. 24. — Left lateral aspect of the ganglion of the mature larva showing
the origin of the nerves, position of the imaginal discs, and anterior end of the
dorsal vessel.
1—11. Eleven segmental nerves, a.b. and c. Nerves arising from the bases
(10-1)
544
C. GORDON HEWITT.
of the stalks of the protlioracic and ventral mesothoracic imaginal discs.
c.l. Cerebral lobe. c.r. Problematical cellular structure (Weismann's " ring ").
d.a'., d.a"., d.a'". Dorsal accessory nerves, d.v. Dorsal vessel, m.c.d.
Major cephalic imaginal discs, ce. (Esophagus, pr.d. Protlioracic imaginal
disc. t. Pine tracheae which arise in association with the segmental nerves,
others arise with some of the more posterior nerves, but for the sake of clear-
ness they are not included in the figure. tr'., tr". Tracheal entering the gan-
glion, v.m.s. Ventral mesothoracic imaginal disc. v.n. Visceral nerve.
Fig. 25. — Longitudinal section of the proventriculus of the mature larva
(Camera lucida drawing.)
c.c. Large cells forming the central hollow core of the proventriculus. ch.i.
Chitinous intima of the oesophagus, e.v. Epithelial cells continuous with and
similar in character to those of the ventriculus. i.e. Ping of imaginal cells.
ce.ep. (Esophageal epithelial cells, v.c. Lumen of ventriculus.
Pig. 26. — The longitudinal lateral tracheal trunk of the left side seen latero-
dorsally showing the origin of the tracheal branches ; small portions only of
the right trunk are shown.
a.com. Anterior tracheal commissure, a.sp. Anterior spiracular process.
f.b. Pat-body. or. I. Oral lobe. l.tr. Longitudinal lateral tracheal trunk.
p.com. Posterior commissure, p.sp. Posterior spiracle, tr' . Trachea entering
ganglion anteriorly, tr" . Trachea entering ganglion laterally, v.tr. Visceral
tracheal trunk,
Pig. 27. — Longitudinal sections through the major cephalic imaginal discs
of mature larva to show the position of the individual imaginal rudiments. The
dextral section is more dorsal than the sinistral. (Camera lucida drawings.)
an.d. Imaginal disc of the antenna, f.d. Pacial imaginal disc. i.s. Sheath
of imaginal rudiments, o.d. Optic imaginal disc. o.g. Imaginal disc of the
optic ganglionic structures, o.s. Optic stalks, s.g. Fundament of the
imaginal supra-oesophageal ganglionic, sh. Sheath of cerebral lobe.
Fig. 28. — Transverse section of mature larva anterior to the ganglion and
cerebral lobes to show the position of certain of the imaginal discs. The body-
wall and muscles have been omitted. The folded character of the adipose
tissue lamina? can be seen in this section, and also the degenerating anterior
portions of the malpighian tubules (m.t.). (Camera lucida drawing.)
an.d. Antennal disc. c.r. Problematical cellular structure (Weismann's
"ring"), c.v. Caecum of ventriculus. d.ms. Dorsal mesothoracic (alar)
imaginal disc. f.c. Adipose tissue cell. l.tr. Lateral tracheal trunk, m.t.
Malpighian tubule cut rather longitudinally, ce. (Esophagus, pr.d. Pro-
thoracic imaginal disc. v.ms. Ventral mesothoracic imaginal disc.
(105)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 545
PLATE 33.
Fig. 29. — Alimentary system of mature larva. The course of the ventriculus
aud intestine as they lie in the larva is shown by the dotted lines. The
origins only of the Malpighian tubes are shown.
c.s.d. Common salivary duct. c.v. Caecum of ventriculus. int. Intestine.
m.t. Malpighian tubule, w. (Esophagus, ph. Pharynx, pv. Proventriculus.
r. Rectum, s.gl. Salivary gland, v. Ventriculus.
Pig. 30. — Transverse section of a portion of the ventriculus of mature
larva. (Camera lucida drawing.)
e.v. Epithelial cell of ventriculus showing large active nucleus and striated
peripheral region of cell. g.s. Probable gland cells, i.e. Group of imaginal
cells.
Pig. 31. Horizontal section of posterior or "cardiac" region of the dorsal
vessel. (Prom camera lucida drawings.)
os. Ostium, v. Valvular flaps guarding the same.
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'100)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 347
The Structure, Development, and Bionomics
of the House-fly, Musca domestica, Linn.
Part III.— The Bionomics, Allies, Parasites, and the Relations
of M. domestica to Human Disease.
By
C. Gordon Hewitt, D.Sc,
Late Lecturer in Economic Zoology, University of Manchester.
With Plate 22.
Contents.
page
I. Introduction . . . . . .348 (107)
n. Distribution . . ... 349 (108)
III. Flies occurring as Co-inhabitants of Houses with M.
domestica or as Visitants .... 351(110)
IV. Physiology :
1. Influence of Food, Temperature, and Light . . 362 (121)
2. Hibernation . . . . .363 (122)
3. Flight . . . . . .364 (123)
4. Regeneration of Lost Parts . . . 365 (124)
V. Natural Enemies and Occasional Parasites :
1. Chernes nodosus, Schrank . . . 367 (126)
2. Acarina or Mites borne by House-flies . . 369 (128)
3. Fungal parasite — Empusa muscse, Oohn . . 371 (130)
VI. Time Parasites :
1. Flagellata — Herpetomonas muscse - domesticae . 374(133)
Crithidia muscte-doniesticoe . 379 (138)
2. Nematoda — Habronema niusca; . . . 380 (139)
3. Dissemination of Pai-asitic Worms . . . 382 (141)
VII. Dissemination of Pathogenic Organisms by M. domestica
and its non-Blood-sucking Allies :
1. Typhoid Fever . . . . .385 (144)
2. Anthrax . . . . .394 (153)
3. Cholera . . . . . . .396 (155)
4. Tuberculosis . . . . .398 (157)
(K'7)
348
0. GORDON UK WITT.
PAGE
5. Ophthalmia . . . . .399 (158)
6. Plague . . . . . .401 (160)
7. Miscellanea . . . . .402 (161)
VIII. Flies and Intestinal Myiasis . . . . 404(163)
IX. Literature ...... 405 (164)
X. Appendix on the Winter Breeding of M. domestioa . 41U (171)
I. Introduction.
The present paper concludes this study of the structure,
development, and bionomics of Muse a domestic a (the
previous parts were published in 1907 and 1908). In it I
have described the bionomics, certain of its allies which may
occur in houses, its pai*asites, and its relation to man, especially
as the carrier of the bacilli of certain infectious diseases.
The last portion of the present paper, in which is described
what is known concerning the ability of M. domestica and
its allies to carry and disseminate the bacteria of many impor-
tant diseases, shows, I hope, the grave character of its relation
to man. Although its importance in this respect is being
gradually realised in this country, it is not so widely recog-
nised as it should be. In the United States of America it is
proposed to change this insect's name from the house-fly to
the " Typhoid fly " ; notwithstanding certain objections to this
name, it clearly indicates that more attention must be paid to
preventive measures, that is, they must be reduced by the
deprivation of suitable breeding-places. I have not discussed
in the present paper the relation of house-flies to infantile or
summer diarrhoea, chiefly because we are not yet certain as to
the specific cause, but this disease may be included for the
present under typhoid or enteric fever in so far as the relation
of flies with it is concerned.
I should like to take this opportunity of thanking those
medical men, whose names I mention later, for the kind
manner in which they have replied to my inquiries concern-
ing their observations on various diseases of which they have
special knowledge.
(iofi)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OT aOUSE-PLT. 349
[I. Distribution.
'Mufsca domstica is probably the most widely distributed
insect to be found ; the animal most commonly associated with
man, whom it appears to have followed over the entire globe.
It extends from the sub-polar regions; where Linnaeus refers
to its occurrence iu Lapland, and Finmark as " rara avis in
Lapponia, at in Finmarchia Norwegiae jntegras domos fere
replet," to the tropics, where it occurs in enormous numbers.
Referring to its abundance in a house near Para, in equatoral
Brazil, Austen (1904) says: "At the mid-day meal they
swarmed on the table in almost inconceivable numbers," and.
other travellers in different tropical countries have related
similar experiences to me, how they swarm round each piece
of food as it is carried to the mouth.
In the civilised and populated regions of the world it occurs
commonly, and the British Museum (Natural History) collec-
tion and my own contain specimens from the following
localities. , Certain of the localities have, in addition, been,
obtained from lists of insect faunas :
Asia. — Aden; North West Provinces (India) ; Calcutta;
Madras; Bombay (it probably occurs over the whole of
India); Ceylon; Central China; Hong-Kong; Shanghai;
Straits Settlements; Japan.
Africa. — Port Said; Suez; Egypt; Somaliland ; Nyassa-
land ; Uganda; British E. Africa; Rhodesia; Transvaal;
Natal ; Cape Colony ; Madagascar ; Northern and Southern
Nigeria ; St. Helena ; Madeira.
America. — Distributed over North America; Brazil;
Monte Video (Uruguay) ; Argentine ; Valparaiso ; West
Indies.
Australia and New Zealand.
Europe and the isles of the Mediterranean; it is especially
common in Cyprus.
Not only is this world-wide distribution of interest^ but its
distribution in our own country is noteworthy. From observa-
tions that I have made during a number of years in town and
(109)
350
C. GORDON HEWITT.
suburban houses and country houses and cottages, I find that
in the former it is by far the commonest house-fly. But
whereas M. domes tica may be almost the only species in
warm places where food is present, such as restaurants and
kitchens, in other rooms of houses Homalornyia cani-
cularis, the small house fly, increases in proportion and
often predominates ; occasionally one may find it to be
commoner than M. domestica. In country houses the
proportions vary by the intrusion of Stomoxys calcitrans,
which I have often found to be the dominant species. In a
certain country cottage, out of the several hundreds captured,
S. calcitrans formed 50 percent, of the total, the rest being
chiefly H. canicular is together with An tho myia radicum,
whose larvae, as I have shown (1907), breed in horse-manure
with those of M. domestica. The following records taken
from a " fly census " that was made in 1907 may be taken as
illustrative of the proportional abundance of the different
species in different situations ; although the numbers of these
records are small the proportions are more obvious.
Place.
M.
domestica.
H . c a n i c u-
laris.
Other species.
Restaurant, Manchester
1869
14
2 (M. stabulans,
C. erythrocephala).
Kitchen, detached sub-
urban house (six records),
Lancashire
581
265
14
Kitchen, detached sub-
urban house in Manchester
682
7
14
Stable, suburban house
22
153
14
(12. S. calcitrans).
Bedroom, suburban house .
1
33
4 (M. stabulans).
Out of a total of 3856 flies caught in different situations,
such as restaurants, kitchens, stables, bedrooms and hotels,
87*5 per cent, were M. domestica, 11*5 per cent. H. canicu-
lar is, and the rest were other species such as S. calcitrans,
Muscina stabulans, C. erythrocephala, and Antho-
myia radicum. These figures are comparatively small, but
(110)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 351
are representative of the average occurrence, as I have
observed, of the different species.
For the proportional occurrence in similar localities we have
interesting figures given by Howard (1900) for the United
States. Of 23,087 flies caught in rooms where food supplies
are exposed he found that 22,808, or 98*8 per cent. . of the
whole number, were M. domestica, and of the remaining
1*2 per cent. H. canicularis was the commonest species.
Hamer (1908) found that more than nine tenths of the flies
caught in the kitchens and "living-rooms" of houses in the
neighbourhood of depots for horse-refuse, manure, etc., were
M. domestica. In a further report Hamer gives more
details as to the different species that were found. In one
lot of 35,000 flies caught on four fly-papers exposed in similar
positions, 17 percent, were Homalomyia canicularis, less
than 1 per cent. wereC. ery throcephala, and considerably
less than 1 per cent, were Muscina stabulans, whereas of
nearly 6000 flies caught in another situation in four fly-
balloons 24 per cent, were H. canicularis, 15 per cent, were
C. ery throcephala, and nearly 2 percent, were M. stabu-
lans. He gives an interesting diagram showing from counts
of flies the seasonal prevalence which 1 have previously
recorded from observation. The report shows how the pro-
portions of the different species vary in different situations
according to the substances and refuse that are present in
the locality. We may therefore say with certainty that
M. domestica is the commonest species of house-fly, and
next to this H. canicularis, and that in country houses
S. calcitrans often occurs in large numbers, although
it is not a house-fly in the strict sense of the word.
III. Flies Occurring as Co-inhabitants of Houses with
M. DOMESTICA OR AS VlSITANTS.
We have seen from the preceding section that M. domes-
tica is by far the commonest species which occurs in houses,
and is, in fact, " domesticated " in the true sense of the word
(Ill)
352
0. GORDON HEWITT.
— Ijinnams never selected a tnore truly specific title;
nevertheless, other species of closely allied flies are found in
houses. These may be either co-inhabitants, tha.t is, living in
houses, as in the case of H. canicular is and one or two
others to be mentioned subsequently, or they may be
visitants. The visitants normally lead an open-air life, but
sometimes, as in the case of Stomoxys calcitrans, they
spend a portion of their time in houses, when climatic condi-
tions are less favourable for out-door life. Such flies as the
blow-fly, or "blue-bottle," Calliphora ery throcephala,
and its allies, enter houses only in search of suitable sub-
stances upon which to deposit their eggs. The appearance in
houses of certaiu flies, as, for example, Pollenia rudis, can
only be regarded as accidental, and the cause may be often
traced to the occurrence of climbing plants such as ivy or other
creepers on the walls of the house,
In India two species of flies closely allied to M. domestica
are found — M uscadomestica sub-sp. d e t e r m i n a t a Walker
and M. enteniata, both of which, ou account of their close
resemblance to M. domestica and the similarity of their
breeding habits, are frequently mistaken for it.
(1) M. domestica sub-sp. deter minata "Walker.
This Indian variety of the house-fly was described by
Walker (1856) from the East Indies. His description is as
follows : " Black, with a hoary covering ; head with a white
covering; frontalia broad, black, narrower towards the
feelers; eyes bare; palpi and feelers black; chest with four
black stripes ; abdomen cinereous, with a large tawny spot on
each side at the base ; legs black ; wings slightly grey, with
a tawny tinge at the base ; prasbrachial vein forming a very
obtuse angle at its flexure, very slightly bent inward from
thence to the tip; lower cross-vein almost straight; alula?
whitish, with pale yellow borders ; halteres tawny."
in appearance and size it is very similar to M . domestica.
Its breeding habits are also similar. Aldridge (1904) states
(11?)
STRUCTURE, DEVELOPM KNT, AND BIONOMICS OE HOUSE-ELY. 353
that at certain seasons of the year it is present in enormous
numbers. The method of disposal of the night soil is to bury
it in trenches about one foot or less in depth. From one
sixth of a cubic foot of soil taken from a trench at Meerut
and placed in a cage, 4042 flies were hatched. Lieut. Dwyer
collected 500 from one cage covering three square feet of a
trench at Mhow. Specimens in the British Museum collection
were obtained from the hospital kitchens, and Smith found
them in a ward at Benares.
They have also been recorded from the N.W. Provinces,
Kangra Valley (4500 feet), Dersa, and I have received speci-
mens from Aden.
(2) Musca enteniata Bigot.
This fly has a distribution somewhat similar to the last
species, and like it, has a marked resemblance to M. domes-
Bigot's (1887) description indicates :
" Front tres etroit, les yeux, toutefois, separes. Antennis et
palpes noirs ; face et joues blanches; thorax nqir avec trois
larges bandes longitudinales grises ; flancs grisatres, ecusson
noir avec deux bandes semblables ; cuille.rons et. balanciers
d'un jaunatre tres pale ; abdomen fauve, avec une bande
dorsale noir et quelques reflets blancs ; pieds noirs; ailes
hyalines; cinquieme nervure longitudinal (Rondin) coudee
suivant un angle legerement arrondi, ensuite un peu concave;
deuxieme transversale (I'extreme) presque perpendiculaire,
legerement bisinueuse, soudee a la cinquieme longitudinale, a
egale distance du conde et de la premiere nervure transversale
(l'interne)."
M. enteniata measures 4 to 5 mm. in length. The British
Museum collection contains specimens sent by Major F. Smith
from Benares, with these notes : " Bred from human ordure ;
hospital ward fly ; at an enteric stool ; bred from cow-dung
fuel cakes." I have received specimens from Suez, and
Aden, and it is recorded as breeding in human excrement in
Khartoum (Balfour, 1908) and in stable refuse, as also M
(113)
354 0. GORDON HEWITT.
domestica and M. corvina. It will be seen, therefore,
that its breeding habits are very similar to those of M.
domestica and the sub-species determinata. It is in-
teresting and important to note the rather exceptional choice
of cow-dung as a breeding-place.
(3) Homalomyia canicularis L.
This species of fly (see 'Quart. Journ. Micr. Sci.,' vol. 51,
PI. 22, fig. 3) is often mistaken by the uninitiated for M.
domestica which are not full grown. Although it may be
called the small or lesser house-fly its differences from M.
domestica are great, as it belongs to a different group of
calypterate Muscidae, namely, the Anthomyidae. One of the
chief distinguishing features of this group is that the fourth
longitudinal vein of the wing (M. 1 + 2) goes straight to the
margin of the wing and does not bend upwards at an angle
as in M. domestica.
The male of H. canicularis differs from the female in
some respects. In the male the eyes are close together, and
the frontal region is consequently very narrow ; the sides of
this, these are the inner orbital regions, are silvery white,
separated by a narrow black frontal stripe. In the female
the space between the inner margins of the eyes is about one
third of the width of the head; the frons is brownish black,
and the inner orbital regions are dark ashy grey. The bristle
of the antenna of H. canicularis is bare; in M. domes-
tica., it will be remembered, the bristle bears a row of setaa
on its upper and lower sides. The dorsal side of the thorax
of the male is blackish grey with thi*ee rather indistinct longi-
tudinal black lines. In the female it is of a lighter grey, and
the three longitudinal stripes are consequently more distinct.
The abdomen of the male H. canicularis is nari'ow and
tapering compared with that of M. domestica. It is bronze
black in colour, and each of the three abdominal segments
has a lateral translucent area, so that when it is seen against
the light, as on a window-pane, three, and sometimes four,
pairs of yellow translucent areas can be seen by the trans-
(114)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 355
mitted light. In the female the abdomen is short in propor-
tion to its length, and is of a greenish or brownish-grey colour
H. canicularis appears in houses before M. domestica,
and can be found generally in May and June. In the latter
month its numbers are swamped, as it were, by M. domes-
tica, and it appears to seek the other rooms of a house than
the kitchen, although I have found it frequently in consider-
able numbers in kitchens. The average length is 5*7 mm.
The larva of H. canicularis (PI. 22, fig. 1) is very
distinct from that of M. domestica, as will be seen from
the figure. It is compressed dorso-ventrally, and has a
double row of processes on each side. Owing to the rough
and spinous nature of these processes dirt adheres to the
larva and gives it a dirty-brown appearance. The full-grown
larva measures 5-6 mm. in length. The breeding habits of
H. canicularis are very similar to those of M. domestica.
The larvae feed on waste vegetable substances and also on
various excremental products, but particularly, I have found,
on human excrement, for which they show a great partiality.
I have frequently found excrement in privy middens to be a
moving mass of the larvae of H. canicularis. The larval
period is from three to four weeks, and the insect spends
fourteen to twenty-one days in the pupal stage.
(4) Homalomyia scalaris F.
Newstead (1907) has found this species occurring as a
house-fly. It is slightly larger than, though similar in many
respects to, H. canicularis. The larva is very similar in
appearance. Newstead found the larva; in ash-pit refuse,
and bred the flies from human faeces. The larvae have been
found frequently to be the cause of intestinal myiasis.
(5) Anthomyia radicum Meigen.
This member of the Anthomyidae has been found in houses,
especially those in or near the country. The female has been
illustrated already (Part I, 'Quart. Journ. Micr. Sci./ vol. 51,
PI. 22, fig. 2). The male is darker in colour, the dorsal side
(115)
356,. 0. G0BD0N HEWITT.
of the thorax being blackish with three black longitudinal
stripes; the frontal region is very narrow; the abdomen is
grey with a dark median stripe. The average length of the
body is 5 mm.
In the. summer they are common and may be found in the
neighbourhood of manure. The eggs are laid in this substance,
especially in horse-manure. The larvse have also been
found feeding on the roots of various cultivated cruciferous
plants, from which the insect has derived the name "root-
maggofc." The eggs hatch out from eighteen to thirty-six
hours after deposition. The first larval stadium lasts twenty-
four hours, the second forty-eight hours, and five days later
the larva changes into a pupa, the whole larval life occupy-
ing about eight days. The pupal stage lasts ten days, so that
in warm weather the develoyjmeut may be completed in nine-
teen to twenty days. The full-grown larvas measure 8 mm.
in length, and may be distinguished by the tubercles sur-
rounding the caudal extremity. In this species there are six
pairs of spinous tubercles surrounding the posterior end and
a seventh pair is situated on the ventral surface posterior to
the anus. The tubercles of the sixth pair, counting from the
dorsal side, are smaller than the rest and are bifid. The
arrangement of the tubercles can be seen in fig. 2. The
anterior spiracular processes (fig. 3) are yellow in colour and
have thirteen lobes.
(6) Stomoxys calcitrans Linn.
The species is common, especially in the country from
July to October, and during these months it may be often
fouud iu houses, although Earner's observations (1908)
appear to indicate that the presence of cowsheds, in which
they occur in large numbers, does not affect their numbers
in houses. I have found S. calcitrans in large numbers
in the windows of a country house in March and April,
and it may be found frequently out of doors on a sunny
day in May, and .throughout the ensuing summer months.
It is normally an outdoor insect', but appears to seek the shelter
(110)
STRUCTURE, DEVELOPMENT, AND BIONOMICS <)K HOUSE-PLY. -'557
of houses, especially during wet weather, from which habit it
has no doubt derived the popular name of " storm-fly " j it is
also know as the "stable-fly." As these names may be equally
applicable to certain other Diptera they should be discarded.
As I have already mentioned this species is frequently mis-
taken by the public for M. domestica, which is supposed to
have adopted the biting habit, although, the latter is unable
to inflict the slightest prick. If examined side by side the
sreat differences between the two will be seen readily (see
Part I in 'Quart. Journ. Micr. Sci., vol. 51, PI. 22, fig. 4).
S. calcitrans has an awl-like proboscis for piercing and
blood-sucking ; this projects horizontally forward from
beneath the surface of the head (fig. 4). It is slightly
larger and more robust than M. domestica; the bristles of
the antennas bear setas on their upper sides only. The colour
is brownish with a greenish tinge ; the dorsal side of the
thorax has four dark longitudinal stripes, the outermost pair
being interrupted. At the anterior end of the dorsal side of
the thorax the medium light-coloured stripe has a golden
appearance, which is very distinct when the insect is seen
against the light. The abdomen is broad in proportion to its
length, and each of the large second and third segments has
a single median and two lateral brown spots ; there is also
a median spot on the fourth segment.
The life-history of S. calcitrans has been studied by
Newstead (1906), aud I have been able to confirm his observa-
tions during 1907 and 1908. From fifty to seventy eggs,
measuring 1 mm. in length, are laid by the female. The eggs
are laid on warm, decaying vegetable refuse, especially in
heaps of fermenting grass cut from lawns ; I have frequently
confirmed this observation of Newstead's. The eggs are also
deposited on various excremental substances upon which the
larvae feed. Osborne (1896) reared them in horse-manure ;
Howard (1900) states that they live in fresh horse-manure,
and records their occurrence in outdoor privies in some
localities ; Newstead reared them in moist sheep's dung ; they
can also be reared in cow-dung.
(H7)
358 0. G0ED0N HEWITT.
The larva? are creamy-white in colour and have a shiny,
translucent appearance. They are rather similar to those of M .
domestica, but can be distinguished by the character of the
posterior spiracles. These (fig. 5 and 6) are wider apart than
in M. domestica and are triangular in shape with rounded
corners; each of tlje corners subtends a space in which a
sinuous aperture lies. The centre of the spiracle is occupied
by a circular plate of chitin. The anterior spiracular pro-
cesses are five-lobed. Under warm conditions Newstead
found that the egg state lasted from two to three days ;
the larval stage lasts from fourteen to twenty-one days
and the pupal stage nine to thirteen days. There are
three larval stages. The whole life-history may be complete
in twenty-five to thirty-seven days. Some specimens passed
the winter in the pupal state.
Although S. calcitrans does not frequent to such a great
extent asM. domestica material likely to contain pathogenic
intestinal bacilli, on account of its blood-sucking habits, which
cause it to attack cattle and not infrequently man, it may
occasionally transfer the anthrax bacillus, as many have
believed, and give rise to malignant pustule, etc.
(7) Calliphora erythrocephala Mg.
This is the commoner of the two English blow-flies or
"blue-bottles." The other species, Calliphora (Musca)
vomitoria, is less common, although the name is frequently
given to both species indiscriminately. They can be dis-
tinguished, however, by the fact that in C. erythrocephala
the genae are fulvous to golden^yellow and are beset with
black hairs, whereas in C. vomitoria the genae are black
and the hairs are golden-red.
The appearance of C. erythrocephala is sufficiently well
known with its bluish-black thorax and dark metallic blue
abdomen. Its length varies from 7 to 13 mm. The larvae
are necrophagous. The flies deposit their eggs on any fresh
or decaying meat, nor is such flesh always dead. On one
occasion, when obtaining fresh material in the form of wild
(11H>
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 359
rabbits upon which to rear the larvae of C. ery throcephala,
I found the broken leg of a live rabbit, which had been caught
in a spring trap set the previous evening, a living mass of
small larvae, which were devouring the animal while it was
still alive. An enormous number of eggs are laid by a single
insect; Portchinski ('Osten. Sacken/ 1887) found from 450
to 600 eggs, though I have not found so many. With an
average mean temperature of 23° 0. (73*5° F.) and using fresh
rabbits as food for the larvae, the following wei*e the shortest
times in which I reared C. ery throcephala. The eggs
hatched from ten to twenty hours after deposition. The laiwae
undervvent the first ecdysis eighteen to twenty-four hours after
hatching ; the second moult took place twenty-four hours later,
and the third larval stage lasted six days, the whole larva life
being passed in seven and a half to eight days. Fourteen days
were spent in the pupal state ; thus the development was com-
plete in twenty-two to twenty-three days. I have no doubt
that this time could be shortened by the presence of a very
plentiful supply of food, as an enormous amount, comparatively,
is consumed.
The full-grown larva may measure as much as 18 mm. in
length. The posterior extremity is surrounded by six pairs
of tubercles arranged as shown in the figure (fig. 12) ; there
is also a pair of anal tubercles. The anterior spiracular
(fig. 11) processes are niue-lobed. The posterior spiracles
(fig. 10) are circular in shape and contain three slit-like
apertures. In the second larval instar (fig. 9) there are only
two slits in each of the posterior spiracles, and in the first
larval instar (fig. 8) each of the posterior spiracles consists of
a pair of small slit-like orifices. Howard (1900) found the fly
on fresh human faeces, and Eiley records it as destroying the
Rocky Mountain locust.
C. ery throcephalais an outdoor fly, but frequently enters
houses in search of material upon which to deposit its eggs
and also for shelter. From its habit of frequenting faeces,
which may be observed in this country especially in insanitary
court-yards, and such food as meat and fruit, it is not improb-
VOL. 54, PAKT 3. NEW SERIES. 26
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C. OORDON EEW1TT.
able that it occasionally may bear intestinal bacilli on its
appendages or body and thus carry infection. Its flesh-seek-
ing habits may also render it liable to carry the bacilli of
anthrax should it have access to infected flesh.
(8) Muscina (Cyrtoneura) stabulans Fallen.
This common species is frequently found in and near houses.
I have usually found it occurring with H . canicularis in the
early summer (June) before M. domes tica has appeared in
any numbers. It is larger than M. domestica, and more
robust in appearance. Its length varies from 7 to nearly
10 mm. Its general appearance is gi'ey. The head is
whitish-grey with a " shot " appearance. The frontal region
of the male is velvety black and narrow ; that of the female
is blackish-brown, and is about a third of the width of the
head. The bristle of the antenna bears seta3 on the upper
and lower sides. The dorsal side of the thorax is grey and
has four longitudinal black lines ; the scutellutn is grey. The
abdomen, as also the thorax, is really black covered with
grey; in places it is tinged with brown, which gives the
abdomen a blotched appearance. The legs are rather slender,
and are reddish-gold or dirty orange and black in colour.
The eggs are laid upon the following substances, on which
the larva? feed : Decaying vegetable substances such as fungi,
fruit, cucumbers, decaying vegetables, and they sometimes
attack growing vegetables, having been introduced probably
as lai va? with the manure, as they also feed on rotting dung
and cow-dung. Howard (1. c.) found the fly frequenting
him an excrement, and observed the species breeding in the
same. In the United States it has been reared from the pupa?
of the cotton-worm and the gipsy moth ; Riley was of the
opinion that in the first case it fed on the rotten pupa? only.
In 1891 it was also reared on the masses of larva? and pupa?
of the elm-leaf beetle. Other observers record it as being
reared from the pupa? of such Hymenoptera as Lophyrus.
In all these cases of its occurrence in the pupa? of insects, it
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 361
is difficult to say whether it is parasitic or whether it feeds on
the rotting pupaa only ; many observers are inclined to take
the last view. The larva may reach a length of 11 mm. It
is creamy-white in colour; the anterior spiracular processes
are five-lobed and are like hands from which the fingers have
been amputated at the first joint. The posterior spiracles
are rounded and enclose three triangular-shaped areas, each
containing a slit-like aperture. I have not been able to study
the complete life-history, but Taschenberg (1. c.) states that it
occupies five or six weeks.
(9) Lucilia Cassar L.
Although it is not a house-fly, this common fly occasionally
occurs in houses, especially those in the country, and it is often
called a "blue-bottle." It is smaller than C. ery throcephala
and is more brilliant in colouring, being of a burnished gold,
sometimes bluish, and also of a shining green colour.
It frequents the excrement of man and other animals in
which it is able to breed. Howard (1. c.) reared it from human
excrement. It also breeds in carrion, but the chief breeding-
place in which I have found it in this country is on the backs
of sheep. It is one of the destructive species of "maggots"
of sheep. The larvae are very similar to those of C . ery thro-
cephala— in fact, Portchinski considered them indistinguish-
able from the larvae of the latter except in size. The full-
grown larva measures 10-11 mm. in length. The larval life
lasts about fourteen days, and the pupal stage a similar length
of time, but I have l'eason to believe that under very favour-
able conditions development may take place in a much
shorter time.
(10) Psychoda spp.
There may be found frequently on window-panes small,
grey, moth-like flies belonging to the family Psychodidas.
The wings of these small flies are large and broad in propor-
tion to the size of the body, and are densely covered with
haii-; when tlie insect is at rest they slope in a roof-like
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362
0. OOKHON EEWITT.
manner. The larvae of some species breed in human and other
excrement, others breed in decaying vegetable substances,
while certain species breed in water, especially when polluted
with sewage, and these aquatic species have the spiracular
apparatus modified accordingly. Although a form, Phlebo-
tamus, which occurs in Southern Europe, has blood-sucking
habits, the British species have no such annoying habits, and
are of little importance in their relation to man.
IV. Physiology.
1. The Influence of Food, Temperature, and Light.
Food. — Mention has already been made in the second part
of this work of the influence of food on the development of the
larvae ; the experiments which were cai'ried out showed that
the larvae develop more rapidly in certain kinds of food, such
as horse-manure, than in others. It has yet to be discovered
what are the chemical constituents which favour the more
rapid development. It was found that insufficient food in the
larval state retarded development and produced flies which
were subnormal in size. Bogdanow (1908), in an interesting
experiment, fed M. domestica through ten generations on
unaccustomed food such as meat and tanacetum in different
pi-oportions, and he found that the resulting flies did not show
any change.
Temperature. — The influence of temperature on the
development of the larvae has been shown also. A high
temperature accelerates the development of the egg, larva
and pupa. Temperature also affects the adult insect; they
are most active at a high summer temperature, and cold
produces an inactive and torpid condition. They are able,
however, to withstand a comparatively low temperature.
Bachmetjew (1906) was able to submit M. domestica to as
low a temperature as — 10° C, aud vitality was retained, as
they recovered when brought into ordinary room temperature.
Donhoff (1872) performed a number of experiments previous
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STRUCTURE, DEVELOPMENT, AND BIONOMICS 01 EO USE-ELY. 363
to this with interesting results. He submitted M. domes-
tica for five houi'S to a temperature of - 1'5° C, and they
continued to move. Exposed for eight hours to a temperature
of first - 3° C. and then - 2° 0. they moved their legs. On
being submitted for twelve hours to a temperature first of
— 3*7° C. and then — 6"3° C, they appeared to be dead, but
on being warmed they recovered. When exposed for three
hours to a temperature of — 10° C. which was then raised
to — 6° C, they died. These experiments show that M.'
domestica is able to withstand a comparatively low degree
of temperature.
Light. — The female of M. domestica deposits the eggs
in dark crevices of the substance chosen for the larval nidus
and as far away from the light as possible. Beclard (1858)
showed that the eggs develop more quickly under blue and
violet glass than under red, yellow, green, or white. The
larvae are negatively heliotropic, as Loeb (1890) has also
proved in the larvae of the blow-fly. As I have previously
shown, the distinction between light and darkness is probably
appreciated by the larvae by means of the sensory tubercles
of the oral lobes.
2. Hibernation.
This question is intimately connected with the preceding
physiological facts. The disappearance of the flies towards
the end of October and in November is a well-known fact,
and an endeavour to discover the reason for this has been
made in the present investigation.
I have found that the majority of flies observed were killed
off by the fungus Empusa muscas Cohn which is described
in the present paper. Of the remainder some hibernate and
some die naturally. This natural death may be compared,
I think, to the like phenomenon that occurs iir the, case of
the hive-bee Apis mellifica, where many of the workers
die at the end of the season hi/ reason of the fact that they
are simply worn out, their function having1 been fulfilled.
The flies which die naturally have probably lived for many
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364
0. GORDON HEWITT.
weeks or mouths during the summer and autumn, and in the
case of the females have deposited many batches of eggs;
their life work, therefore, is complete. Those flies which
hibernate are, I believe, the most recently emerged, and
therefore the youngest and most vigorous. On dissection it
is found that the abdomens of these hibernating individuals
are packed with fat cells, the fat body having developed
enormously. The alimentai'y canal shrinks correspondingly
and occupies a veiy small space; this is rendered possible by
the fact that the fly does not take food during this period.
In some females it was found that the ovaries were very well
developed, while in others they were small, and mature
spermatozoa were found in the males. Like most animals in
hibernating, M. domestica becomes negatively heliotropic
and creeps away into a dark place. In houses they have been
found in various kinds of crevices such as occur between the
woodwork and the walls. A favourite place for hibernation
is between wall-paper which is slightly loose and the wall.
A certain number hibernate in stables, where, owing to the
warmth, they do not become so inactive, and they emerge
earlier at the latter end of spring. During the winter the
hibernating flies are sustained by means of the contents of
the fat body, which is found to be extremely small in hiber-
nating flies if dissected when they first emerge in May and
June. The abdominal cavity is at first considerably decreased
in size, but the fly begins to feed and soon the alimentary
tract regains its normal size, and, together with the develop-
ment of the reproductive organs, causes the abdomen to
regain its normal appearance. The emergence from hiber-
nation appears to be controlled by temperature, as one may
frequently find odd flies emerging from their winter quarters
on exceptionally warm days in the early months of the year
(see Appendix).
3. Flight.
The distance that M. domestica is able to fly is one of
practical importance in connection with their breeding habits
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STBUOTURE, DEVELOPMENT, AND BIONOMICS OF EOUSE-FLY. 365
and disease-germ-carrying powers. Normally they do not fly
great distances. They may be compared to domestic pigeons
which hover about a house and the immediate neighbourhood.
On sunny days they may be found in large numbers out-of-
doors, but they retire into the houses when it becomes dull or
rains. They are able to fly, however, a considerable distance,
and can be carried by the wind. A few years ago, when
visiting the Channel Islands, I found M. domestica from
1y to 2 miles from any house or any likely breeding-place,
so far as I was able to discover. Dr. M. B. Aimold has
made some exact experiments at the Monsall Fever Hospital,
Manchester, on the distance travelled by Hies.1 Three hundred
flies were captured alive, and marked with a spot of white
enamel on the back of the thorax. These were liberated in
fine weather. Out of the 300 five were recovered in fly-traps
at distances varying from 30 to 190 yards from the place of
liberation, and all the recoveries were within five days.
M. domestica is also able to fly at a considerable height
above ground, and I have found them flying at an altitude of
80 feet above the ground. Such a height would greatly
facilitate their carriage by the wind.
4. Eegeneration of Lost Parts.
If the wings or legs of M. domestica are broken off they
do not appear to be able to regenerate the missing portions,
as in the case of some insects, notably certain Orthoptera.
Kammerer (1908), however, experimenting with M. domes-
tica and C. vomitoria, has found that if the wing is
extirpated from a recently pupated fly it is occasionally
regenerated. The new wing is at first homogeneous, and con-
tains no veins, but these appear subsequently.
1 Kecorded on p. 262 of the ' Report on the Health of the City of
Manchester for 1906,' by James Niven, 1907.
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366
0. GOEDON HEWITT.
V. Natural Enemies and Occasional Parasites.
The most important of all the natural enemies of M.
domestica is the parasitic fuugus Empusa muscae, which
will be described here ; this is the most potent of the natural
means of destruction/ Of animals, apart from the higher
animals such as birds, spiders probably account for the
greatest number, though owing to the normally clean con-
ditional' the modern house these enemies of the house-fly are
refused admittance. I have been unable to rear any insect
parasites, such as ichneumons, from M. domestica. Their
life indoors and the cryptic habits of the larvas^no doubt save
them from the attacks of such insects; but- Packard (1874)
records the occurrence of the pupa of what was probably a
Dermestid beetle, which he figures ; this was found in a pupa
of M. domestica. Predatory beetles and their larvae pro-
bably destroy the larvaa, and Berg (1898) states that a species
of beetle, Trox suberosus F., known as "Champi" in
S. America, is an indirect destructor of the common fly. I
have frequently obseiwed the common wasp, Vespa ger-
manica, seize M. domestica and carry it away. In some
places in India it is the custom, so I have been told by resi-
dents, to employ a species of Mantis, one of the predatory
" praying insects," to destroy the house-flies^/
In view of the fact that the Arachnids Chernes nodosus
and the species of Gramasid are occasionally found actually
attached in a firm manner to M. domestica, they will be
described under this head, but it must be clearly understood
that it is still an open question whether they are external
parasites in the true sense of the word, or whether M. domes-
tica, instead of being the host, is merely the transporting
agent as it appears to be in the majority of cases. For the
present they may be termed for convenience "occasional
parasites/' in view of the fact that they have been found
occasionally feeding upon M. domestica.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 367
f~ 1. Cherries nodosus Schrank.
There are frequently found attached to the legs of the
house-fly small scorpion or lobster-like creatures which are
Arachnids belonging to the order Pseudo-scorpionidea;
the term "chelifers" is also applied to them on account of the
large pair of chelate appendages which they bear. The
species which is usually found attached to M. domestica is
Chernes nodosus Schrank (fig. 13). It is very widely
distributed, and my observations agree with those of Pickard-
Cambridge (1892), who has described the group.
The species is 2*5 mm. in length/and Pickard-Cambridges's
description of it is as follows :
" Cephalothorax and palpi yellowish red-brown, the former
rather duller than the latter. Abdominal segments yellow-
brown ; legs paler. The caput and first segment of the
thorax are of equal width (from back to front) ; the second
segment of the thorax is very narrow. The surface of
the cephalothorax and abdominal segments is very finely
shagreened, the latter granulose on the sides. The hairs on
this part as well as on the palpi and abdomen are simple, but
obtuse. The palpi are rather short and strong. The axillary
joint is considerably and somewhat subconically protuberant
above as well as protuberant near its base underneath. The
humeral joint at its widest part, behind, is considerably
less broad than long ; the cubital joint is very tumid on its
inner side ; the bulb of the pincers is distinctly longer, to the
base of the fixed claw, than its width behind; and the claws
are slightly curved and equal to the bulb in length/'
They appear to be commoner in some years than in others.
Godfrey (1909) says: " The ordinary habitat of Ch. nodosus,
as Mr. Wallis Kew has pointed out to me, appears to be among
refuse, that is, accumulations of decaying vegetation, manure-
heaps, frames and hot-beds in gardens. He refers to its occur-
rence in a manure-heap in the open air at Lille, and draws my
attention to its abundance in a melon-frame near Hastings in
1898, where it was found by Mr. W. R. Butterfield." In
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368
C. GORDON HEWITT.
view of these facts it is not difficult to understand its frequent
occurrence on the legs of flies, which may have been on the
rubbish heaps either for the purpose of laying eggs, or, what
is more likely, because they have recently emerged from
pupas in those places and in crawling about, during the pro-
cess of drying their wings, etc., their legs were seized by the
C. nodosus.
The inter-relatiou of the Chernes and M. domestica,
however, is one of no little complexity; much has been
written and many diverse views are held concerning it. An
interesting historical account of the occurrences of these
^rachnids on various^ insects has been given by Kew (1901).
Three views are held in explanation of the association and
they are briefly these : First, that the Chernes, by clinging
passively to the fly, uses it as a means of transmission and
distribution ; second, that the Ai'achnid is predaceous ; and
third, that it is parasitic on the fly. Owing to the unfortunate
absence of convincing experimental proof in favour of either
of the last two opinions, it is practically impossible to give
any definite opinion as to the validity of these views ; never-
theless they are worthy of examination^/
The dispersal theory was held by Pickard- Cambridge and
Moniez (1894). Whether the other views are held or not
there is no doubt that such an association, eveu if it were
only accidental, would result in a wider distribution of the
species of Chernes, as the flies are constantly visiting fresh
places suitable as a habitat for the same. Except in one or
two recorded cases the Arachnids are always attached to the
legs of the fly, the chitin of which is hard and could not be
pierced, a fact which is held in support of this theory as the
only explanation of the association.
The parasitic and predaceous views are closely related.
The Pseudo-scorpionidea feed upon small insects, which
they seize with their chelae. It is suggested by some that
the Chernes seizes the legs of the fly without realising the
size of the latter. Notwithstanding its size, however, they
remain attached until the fly dies and then feed upon the
»
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STRUCTURE, DEVELOPMENT, AKfD BIONOMICS 01 HOUSE-FLY. 369
body. In some cases as many as teu of the Arachnids have
been found on a single fly, and if the movements of the
insect are impeded by the presence of a number of the
Chernes it will be easily understood that the life of the fly
will be curtailed thereby. Pseudo -scorpionidea have been
observed feeding on the mites that infest certain species of
Coleoptera, and it has been suggested that they associated
with the flies for the same purpose, although I do not know
of any recoi'ded case of a fly infested with mites carrying
Chernes also. If this were the case the Chernes would be
a friend and not a foe of the fly, as Hickson (1905) has
pointed out.
There are few records to support the view that the Chernes
is parasitic on the flv^, Donovan (1797) mentions the occur-
rence of a pseudo-scorpionid on the body of a blow-fly, and
Kirby and Spence (1826) refer to their being occasionally
parasitic on flies, especially the blow-fly, under the wings of
which they fix themselves. It is probable that the Chernes
seldom reaches such a position of comparative security on the
thorax of the fly ; should it succeed in doing so, however, it
could become parasitic in the true sense of the word. As I
have previously pointed out, little experimental evidence is at
present available and further investigation is necessary before
it is possible to maintain more than a tentative opinion with
regard to this association between the Chernes and the
fly. It is obvious that the association will result in the dis-
tribution of the Pseudo-scorpionid, but whether this is
merely incidental and the real meaning lies in a parasitic or
predaceous intention on the part of the Arachnid, as some of
the observations appear to indicate, further experiments alone
will show.
2. Acarina or Mites borne by House-flies.
As early as 1735 de Geer observed small reddish Acari in
large numbers on the head and neck of M. domestica.
They ran about actively when touched. The body of this
mite was oval in shape, completely chitinised, and polished ;
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370
0. CORDON HEWITT.
the dorsal side was convex aud the ventral side flat. Linnaeus
(1758) called this mite Acarus muscaruni from de Greer's
description, and Geoff roy (1764) found what appears to be
the same, or an allied species of, mite, which he called the
"brown fly-mite." Murray (1877) describes a form, Trom-
bidium parasiticum,1 which is a minute blood-red mite
parasitic on the house-fly. He says : " In this country they
do nob seem so prevalent, but Mr. . Biley mentions that in
North America, in some seasons, scarcely a fly can be caught
that is not infested with a number of them clinging tenaciously
round the base of the wings." As it only possessed six legs
it was doubtless a larval form.
Anyone who has collected Diptera as they have emerged
from such breeding-places as hot-beds, rubbish and manure
heaps will have noticed the frequently large number of these
insects which are to be found carrying immature forms of the
Acari. These are being transported merely by the flies in
the majority of cases. Mr. Michael tells me that he used to
call such flies "the emigrant waggons " — a very descriptive
term. Many of these mites belong to the group Gamasidae —
the super-family Gamasoidea of Banks (1905). These mites
have usually a hard coriaceous integument. In shape they are
flat and broad and have rather stout legs. Sometimes imma-
ture forms of these mites swarm on flies emerging from rubbish
heaps. Banks holds the opinion that they are not parasitic,
but that the insect is only used as a means of transportation.
It is difficult to decide whether this is so in all cases. I have
illustrated (fig. 14) a specimen of the small house-fly, H.
canicularis, caught in a room ; on the under-side of the fly's
abdomen a number of immature Gamasids 2 ai-e attached,
1 This species was named Atoma parasiticum and later Astoma
parasiticum by Latreille (' Magazin Encyclopedique." vol. iv. p. 15.
1795). Mr. A. D. Michael tells me that the genus was founded on
Trombidium parasiticum of de Geer. They were really larval
Trouibidiidse and Atoma was founded on larval characters ; probably
any larval Trombidium came under the specific name.
2 Being unable to identify these immature specimens I submitted
them to Mr. Michael, who kindly informs me that it is extremely diffi-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF EOUSE-FLY. 371
apparently by their stomal regions. These specimens may be
truly parasitic, as I am inclined to believe, since many Acari
are parasitic in the immature state, although the adults may
not be so; on the other hand this form of attachment may be
employed as a means of maintaining a more secure hold of
the transporting insect.
3. Fungal Disease — Empusa muscaa Cohn.
Towards the end of the summer large numbers of flies may
be found attached in a rigid condition to the ceiling, walls or
window-panes. They have an extremely life-like appearance,
and it is not until one examines them closely or has touched
them that their inanimate, so far as the life of the fly is con-
cerned, condition is discovered. These flies have been killed by
the fungus Empusa nauseas Cohn, and in the later stages of
the disease its fungal nature is recognised by the fact that a
white ring of fungal spores may be seen around the fly on the
substratum to which it is attached. The abdomen of the fly
is swollen considerably, and white masses of sporogenous
fungal hyphae may be seen projecting for a short distance
from the body of the fly, between the segments, giving the
abdomen a transversely striped black and white appearance.
The majority of flies which die in the late autumn — and it
is then that most of the flies which have been present during
the summer months perish — are killed by this fungus. Its
occurrence, therefore, is of no little economic value, especially
if it were possible to artificially cultivate it and destroy the
flies in the early summer instead of being compelled to wait
until the autumn for the natural course of events.
Empusa muscae belongs to the group Entoinoplithoreae,
the members of which confine their attacks to insects, and in
many cases, as in the case of the present species, are produc-
tive of great mortality among the individ nals of the species of
cult to identify immature Gamaeids owing to the scarcity of knowledge
as to their life-histories, but lie says that they are very like Dinychella
asperata Berl.
131)
372
0. GORDON HEWITT.
insect attacked. In this country it may be found from about
the beginning of July to the end of October, and usually
occurs indoors. It appears to be very uncommon out-of-
doors. A case has been recently recorded1 of its occurrence
on Esher Common, where it had attacked a species of Syrphid,
Melanostomum scalare Fabr. Thaxter (1888) also
mentions two cases of its occurrence out-of-doors in America,
in both of which cases it had attacked, singularly enough,
species of Syrphidte. This author states that Empusa
m us cse is probably the only species which occurs in flowers
attractive to insects, but he only observed it on the flowers of
So lid a go and certain Umbel 1 if ereas.
The development of this species was studied by Brefeld
(1871). An E mpusa spore which has fallen on a fly rests
among the hairs covering the insect's body and there adheres.
A small germinating hypha develops, which pierces the
chitin, and after entering the body of the victim penetrates
the fat-body. In this situation, which remains the chief
centre of development, it gives rise to small spherical struc-
tures which germinate in the same manner as yeast cells,
forming gemmae. These separate as they are formed, and
falling into the blood sinus are carried throughout the whole
of the body of the fly. It was probably these bodies that
Cohn (1855) found, and he explained their presence as being
due to spontaneous generation ; he believed that the fly first
became diseased and that the fungus followed in consequence.
After a period of two or three days the fly's body will be
found to be completely penetrated by the fungus, which
destroys all the internal tissues and organs. The whole
body is filled with the gemmae, which germinate and produce
ramifying hyphae (fig. 15). The latter pierce the softer
portions of the body-wall between the segments and produce
the short, stout conidiophores (c), which are closely packed
together in a palisade-like mass to form a compact white
cushion of conidiophores, which is the transverse white ring
that one finds between each of the segments of a diseased, and
1 ' Trans. Ent. Soc. London,' 1908 (" Proceedings," p. 57).
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE EOUSE-FLY. 373
consequently deceased, fly, A conidium now develops
(fig. 16) by the constriction of the apical region of the
conidiophore. When it is ripe the conidium (fig. 17) is
usually bell-shaped, measuring 25-30 '/x in length; it generally
contains a single oil-globule (o.g.). In a remarkable manner it
is now shot off from the conidiophore, often for a distance of
about a centimetre, and in this way the ring or halo of white
spores, which are seen around the dead fly, are formed. In
some cases, although I find that it is not an invariable rule as
some would suggest, the fly, when dead, is attached by its
extended proboscis to the substratum. Griard (1879) found
that blow-flies killed by Entomophthora calliphora were
attached by the posterior end of the body. If the conidia,
having been shot off, do not encounter another fly, they have
the power of producing a small conidiophore, upon which
another conidium is in turn developed and discharged. If
this is unsuccessful in reaching a fly a third conidium maybe
produced, and so on. By this peculiar arrangement the
conidia may eventually travel some distance, and it is no
doubt a great factor in the wide distribution of the fuugus,
once it occurs. On the fly itself short conidiophores may be
found producing secondary conidia.
Reproduction by conidia appears to be the only form of
generation, as we are still uncertain as to the occurrence of a
resting-spore stage in this species. Winter (1881) states
that he found resting-spores in specimens of M. domestica
occurring indoors; they also produced conidia which he
identified as E. muscse. These azygospores measured
30-50 /j. in diameter, and were produced laterally or termin-
ally from hyphse within the infected fly. Giard (1. c.) describes
resting spores which were produced externally and on
specimens found in cool situations. Brefeld, however, is of
the opinion that E. muscae does not produce resting-spores.
The question of the production of resting-spores needs further
investigation, as it is one of some importance. In the absence
of confirmatory evidence it is extremely difficult to understand
how the gap in the history of the Em pus a, between the
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374
C. GOfiDON EE WITT.
late autumn of oue year and the summer of the next, is filled.
A number of suggestions have been made, many of which
cannot be accepted ; for example, Brefeld believes that the
Empusa is continued over the winter in warmer regions,
migrating northwards with the flies on thei'eturn of summer!
In the case of Entomophthora calliphora, Griard believes
that the cycle is completed by the corpses of the blow-flies
falling to the ground, when the spores might germinate in the
spring and give rise to conidia which infect the larvae. Olive
(1906) studied the species of Empusa which attacks a species
of Sciara (Diptera) and found the larvas infected. He
accordingly thinks that the disease may be carried over the
winter by those individuals which breed during that period in
stables and other favourable places. As I have shown,
M. domestic a, under such favourable conditions as warmth
and supply of suitable larval food, is able to breed during the
winter months, although it is not a normal occui*rence so far
as I have been able to discover. If, then, these winter-pro-
duced larvae could become infected they might assist in
carrying over the fungus from one year to the next, and thus
carry on the infection to the early summer broods of flies.
This suggestion and the possible occurrence of a i*esting-spore
stage appears to me to be the probable means by which the
disease may be carried over from one " fly-season " to the next.
E. muscae, besides occurring in M. domestica, has been
found on several species of Syrphidae, upon which it usually
occurs out-of-doors, as I have already mentioned. In addi-
tion to these Thaxter records its occurrence in Lucilia
caesar and Calliphora vomitoria.
VI. Trcjk Pabasites.
1. Plagellata. Herpetomonas rnuscae-domesticas
Burnett.
This flagellate has been known as a parasite of the ali-
mentary tract of M. domestica for many years. Stein
(1878) figures a flagellate which he calls Cercomonas
in u scae-domestica, and identifies it with the Bodo muscae-
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STRUCTURE, DEVELOPMENT, AND BEONOMCCS OP HOUSE-PLY. 375
domesticas described by Burnett and the Cercomonas
muse arum of Leidy. For this form figured by Stein, a new
genus, Herpetomonas, was instituted by Kent (1880-81),
and it is taken as the type-species. It was not until the
economic importance of certain of the haemo-flagellates was
recognised that other flagellates, including H. muscae-
domesticas, received further attention, and then Prowazek
(1904) described with great detail the development of this
species. In the previous year Leger (1903) had given a short
account of it, and since Prowazek's memoir Patton (1908,
1909) has given short preliminary accounts of his study of
the life-history. The accounts of both these authors differ in
several respects from that of Prowazek, as will be shown. I
have examined a very large number of the contents of English
specimens of M. domestica, but, with one or two doubtful
exceptions, unfortunately I have been unable so far to
discover any of these flagellates in my film preparations.
The full-grown flagellate (VIII) measures 30-50 /u in
length. The body is flattened and lancet-ska/ped, the pos-
terior end being pointed and the anterior end bluntly rounded.
The alveolar endoplasm contains two nuclear structures. In
the centre is the large " ti*ophonucleus " (tr.) ; it contains
granules of chromatin, but is sometimes difficult to see. Near
the anterior end the deeply staining rod-shaped "kineto-
nucleus" (blepharoplast of many authors) (/c.) lies, usually in
a transverse position. The single stout flagellum, which is a
little longer than the body of the flagellate, arises from the
anterior end, near the kinetonucleus. Prowazek describes the
flagellum as being of a double nature and having a double
origin ; this, which is a mistaken interpretation, is repeated
by Lingard and Jennings (19D6).
This mistake, as pointed out by Leger and Patton, is due to
the fact that the majority of the adult flagellates have the
appearance of a double flagellum, which represents the
beginning of the longitudinal division of the flagellate (VI).
Patton (1908) figures a stage in H. lygaai with the double
flagellum, and Leger (1902) in a similar stage in H . jaculum,
VOL. 54, PART 3. NEW SERIES 27
Di agrarn of the life-cycle of Herpetomonas muscse-domes-
ticae Burnett. Arrangement chiefly after Patton ; figures
after Leger, Patton, and Prowazek. I-III. Pref lagellate
stage. IV- VIII. Flagellate stage : V. Young flagellate.
VI. Flagellate beginning to divide, flagellum having already
divided. VII. Advanced stage of division. VIII. Adult
flagellate. IX-XI. Post-flagellate stage: IX. Degene-
ration of flagellum. Xa. Post-flagellate stage completed by
formation of gelatinous covering, containing double row of
granular bodies (Prowazek). f.v. Flagellar vacuole. 7s. Kineto-
nucleus. s.t. Spiral chromophilous thread, tr. Trophonucleus.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 377
parasitic in the gut of Nepa cinerea, from which figures it
may be understood how the mistake has arisen. Through
this misinterpretation Prowazek was led to consider that the
parasite was of a bipolar type, in which the body had been
doubled on itself so that the two ends came together and the
flagellum remained distinct. The flagellum, according to
Leger, is continued into the cytoplasm as a thin thread,
which stains with difficulty, and terminates in a double
granule above the kinetouucleus ; this double granule is no
doubt the "diplosome" of Prowazek. According to the
latter author another deeply staining double thread (s.t.),
that appeal's to be spirally coiled, runs backwards from the
kinetonucleus and terminates posteriorly in a distinct granule,
shown in fig. VIII.
The flagellates congregate in the proventi'iculus or in the
posterior region of the intestine, where they become united
by their anterior ends to form rosettes. Prowazek states that
in the rosette condition the living portion of the flagellate
resides, as it were, in the long tail-like process.
Patton divides the life-cycle of H. mu scee-domesticas
into three stages — the preflagellate, flagellate, and post-
flagellate. The last two are common, but the first stage is
not common, and Prowazek appears to have overlooked, it.
For convenience I have described the flagellate stage first,
and the process of division in this stage is simple longitudinal
fusion. The nuclei divide independently, and the kineto-
nucleus usually precedes the trophonucleus. The latter
undergoes a primitive type of mitosis, in which Prowazek
recognised eight chrosomes (VII). The flagellum divides
longitudinally, and each of the two halves of the kineto-
nucleus appropriates one of the halves with its basal granule.
The pi*eflagellate stage, which Patton (1909) describes,
usually occurs in the masses which lie within the peritrophic
membrane.1 They are round or slightly oval bodies (I), their
average breadth being 5*5 fx. The protoplasm is granular and
1 I assume that Patton refers to this membrane by the term " peri-
tricheal membrane."
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378
0. GORDON HEWITT.
contains a trophonucleus and kinetonucleus. Division takes
place by simple longitudinal division or multiple segmenta-
tion, and in this manner a large number of: individuals are
formed (II b and III) . These develop into the flagellate stage :
a vacuole, the flagellar vacuole (III, /.v.) appears between the
kinetonucleus and the rounded end of the pre-flagellate form,
and in it the flagellum appears as a single coiled thread, which
is extended when the vacuole has approached the surface.
The flagellate form has already been described, and in the
concluding portion of the flagellate stage, which, according
to Prowazek, is found in starved flies, these forms are found
collecting in the rectal region, and attaching themselves by
their flagellar ends in rows to gut epithelium. The more
external ones begin to shorten, during which process the
flagella degenerate (IX) and are shed. Thus a palisade of
parasites is formed, the outer oues being rounded and devoid
of flagella, and some of them may be found dividing (X).
Leger (1902) terms these the "formes gregariennes," and
maintains that the existence of these "gregarine" forms is a
powerful argument in favour of the flagellate origin of the
Sporozoa, which he had previously suggested, and which
Biitschli had put forward in 1884. After the degeneration of
the flagellum a thickened gelatinous covering is formed, con-
taining a double row of granular bodies (Xa), and these cysts
are regarded by Patten as the post-flagellate stage. They
pass out with the fasces, and dropping on the moist window-
pane or on food, are taken up by the proboscides of other flies.
Prowazek describes dimorphic forms of the flagellate stage,
which he regards as sexually differentiated forms, but Patton,
in a letter to me, says that he is unable to find any of these
complicated sexual stages. According to Prowazek, one of
these forms is slightly larger than the other, and has a greater
affinity for stain. The dimorphic forms conjugate; their cell
substance and nuclei fuse, and a resting-stage cyst is formed,
but the subsequent stages have not been followed. He
further states that the sexually differentiated forms may force
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 379
their way into the ovaries, where they undergo autogamy
and infect the subsequent brood. '
In Madras Patton found that 100 per cent, of the flies were
infected with the flagellate ; Provvazek found it in 8 per cent,
of the flies at Rovigno. In the cold season in the plains
(India) Lingard and Jennings (I.e.) found the. flagellate in
less than 1 per cent, of the flies examined ; in the hills
(Himalayas), at an elevation of 7500 feet, the flagellates were
most numerous during the hottest season of the year, and
gradually decreased in number to October and November,
when none were discovered.
One of the chief points of interest in connection with this
flagellate is its similarity to the " Leishmann-Donovan "
bod}r, the parasite of kala-azar, as it was this resemblance
that prompted Rogers (1905) to suggest that the latter
parasite was a Herp'etomonas, which I think Patton has
now conclusively proved to be the case, and he calls it
Herpetomonas donovani (Laveran and Mesnil).
Crithidia Muscas-doniesticas Werner.
This parasite has been recently described by Werner (1908),
who found it in the alimentary tracts of four out of eighty-two
flies. It measures 10-13 fx in length, the length of the body
being 5—7 fx and the flagellum 5-6 ju. As in other members
of the genus Crithidia, which, is closely allied to Herpeto-
monas, the breadth of the body is great compared with the
length, and the kinetonucleus and trophonucleus are rather
close together. A short, staining, rod-like body lies between
the kinetonucleus and the base of the flagellum. The flagellum
is single. Dividing forms undergoing longitudinal division
were frequently found. The kinetonucleus appears to divide
first, followed in succession by the flagellum and the tropho-
nucleus. Forms undergoing division and showing a single
trophonucleus and double kinetonucleus and flagellum were
also found. Cases occurred in which the fission began at the
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380
C. GORDON HEWITT.
non-flagellate end of the body. No conjugating forms were
found, nor any wandering into the ovaries.
Lingard and Jennings (1. c.) describe certain flagellates of a
flag-shaped or rhomboidal nature, which I am strongly of the
opinion are species of Crithidia and not species of He r-
petomonas. Closely following Prowazek's account of H.
muscas-domesticas they describe and figure all their forms
as having two flagellas in the flagellate stage. If one allows
for the rupture of the flagellum from the bodies of the
organism in making the film, some of their figures are not
unlike those of Crithidia gerridis, parasitic in the alimen-
tary tract of an Indian water-bug, Cerris fossarum Fabr.,
and described by Patton (1908).
2. Nematoda — Habronema muscae (Carter).
Carter (1861) appears to be the first to have described
a pai'asitic worm in M. domestic a. He described a bi-
sexual nematode infesting this insect in Bombay, and found
that : "Every third fly contains from two to twenty or more
of these worms, which are chiefly congregated in, and con-
fined to, the proboscis, though occasionally found among the
soft tissues of the head and posterior part of the abdomen."
His description of this nematode, to which he gave the name
Filaria muscse, is as follows: "Linear, cylindrical, faintly
striated transversely, gradually diminishing towards the
head, which is obtuse and furnished with four papilla? at a
little distance from the mouth, two above and two below ;
diminishing also towards the tail, which is short and termi-
nated by a dilated round extremity covered with short spines.
Mouth in the centre of the anterior extremity. Anal orifice
at the root of the tail." He gives the length as being one
eleventh of an inch and the breadth as one three hundred and
thirteenth of an inch. In his description of his figures of the
worm he calls what is evidently the anterior region of the
intestine the " liver." Von Linstow (1875) described a small
nematode, which he calls Filaria stomoxeos; from the
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 381
head of S. calcitrans ; this larva measured 1*6 to 2 mm. in
length. Generali (1886) described a nematode froin the
common fly, which he calls Nematodum spec. It is
highly probable, as my friend Dr. A. E. Shipley has suggested
to me, that Generali' s nematode and the F. muse as of Carter
are identical. Diesing (1861) created the genus Habronema
for the Filaria muscaa of Carter, and his description is
practically a translation of Carter's original description.
Piana (1896) describes a nematode from the proboscis of M.
domestica, which, in the occurrence of the male and female
genital organs in the same individual, he says, resembles
Carter's nematode. He finds that at certain seasons of the
year and in certain localities it is very rare, while at others it
may occur in 20-30 per cent, of the flies. The larva, after
fixation, measured 2'68 mm. in length and 0'08 mm. in breadth.
It was cylindrical and gently taperiug off at the extremities,
with the mouth terminal.
Out of the many hundreds of flies which I have dissected I
have only found two specimens of this nematode (fig. 18). From
the descriptions given by Carter and Piana and the figures of
the latter I feel convinced that their specimens and mine are
the same species, called by Diesing Habronema muscse
(Carter). It is linear, cylindrical, tapering gradually towards
both ends. The anterior end is slightly rounded, having the
mouth in the centre. I am unable to confirm the presence of
the four papillae which Carter describes as a little distance
from the mouth, nor are they figured by Piana. The cuticle
is very faintly marked with transverse striations. The
common genital and anal orifice is situated at a short distance
from the posterior end of the body, which tapers off slighly
more than the anterior end and terminates in a small dilated
extremity, which is covered with minute spines (fig. 19). My
specimens appear to be immature adult forms, not having
reached sexual maturity. The species measures 2 mm. in
length and 0"04 mm. in breadth. The specimens that I
obtained were situated in the head region, between the optic
ganglia and the cephalic air-sacs, from which position they
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382
C. GORDON HEWITT.
could easily move clown into the cavity of the proboscis. I
am unaware of any previous record of the occurrence of
Habronema muscle in this country, but I have no doubt
that if one searched specially for it it would be found to
occur more commonly than might appear from my experience,
and to be generally distributed with its host throughout the
world.
The occurrence of a parasitic worm in this position is of
great interest, even though M. domestica is not a blood-
sucking species and the nematode is not of the nature of
Filaria bancrofti. There is no reason, however, why M.
domestica should not under certain conditions carry patho-
genic nematodes, which might easily get on to the food of
man.
3. Dissemination of Parasitic Worms.
In this connection reference might be made to the experi-
ments of Grrassi (1883) to which reference is made by Nuttall
in his valuable memoir (1899). Grassi broke up segments of
Taenia solium in water; they had previously been preserved
in alcohol for some time. Flies sucked up the eggs in the
water and he found them unaltered in the faeces. Oxyuris eggs
were also passed unaltered. In another experiment hies fed
on the eggs of Trichocephalus and he found the eggs some
hours afterwards in the flies' fasces, which had been deposited
in the story beneath the laboratory ; he also caught flies in
this kitchen with their intestines full of eggs.
Calandruccio1 examined flies (? species) which had settled
upon fasces containing the ova of Taenia nana. The ova
were found in the flies' intestines. The excrement deposited
by a fly on sugar contained two or three ova of the Taenia.
By means of such infected sugar a girl was infected, and ova
of T. nana were found in her stools on the twenty-seventh
day.
1 "Ulteriori ricerche sulla Taenia nana," 'Boll. Soc. Zool. Ital.
Roma,' vol. vii, pp. 65-69 ; also in ' Boll. Acad. Gioenia, Catania,' Fasc.
89, pp. 15-19.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 383
Nuttall (1. c.) records a personal communication of Stiles,
who placed the larvae of Musca with female Ascaris lum-
bricoides, which they devoured together with the eggs
contained by the nematodes. The larvae and adult flies con-
tained the eggs of the Ascaris, and as the weather at the
time of the experiment was very hot the Ascaris eggs
developed rapidly and were found in different stages of
development in the insect, thus proving, as Nuttall points
out, " that the latter may serve as disseminators of the
parasite." These experiments of Grassi and Stiles show that
flies can act as carriers of the eggs of these parasitic worms,
and that man could be infected by the fly depositing its
excreta on his food, or being accidentally immersed in food
as flies frequently are.
VII. The Dissemination op Pathogenic Organisms by
Musca domestica and its non-Blood-sucking Allies.
Although M. domestica is unable to act as a carrier of
pathogenic micro-organisms in a manner similar to that of
the mosquito, so far as we know at present, nevertheless its
habits render it a very potent factor in the dissemination of
disease by the mechanical transference of the disease germs.
These habits are the constant frequenting and liking for
substances used by man for food on the one hand and excre-
mental products, purulent discharges, and moist surfaces on
the other. Should these last contain pathogenic bacilli, the
proboscis, body, and legs of the fly are so densely setaceous
(see fig. 20) that a great opportunity occurs, with a maximum
amount of probability, for the transference of the organisms
from the infected material to either articles of food or such
moist places as the lips, eyes, etc. As I have already pointed
out (1907), M. domestica is unable to pierce the skin, as
certain persons have suggested. The structure of the pro-
boscis will not permit the slightest piercing or pricking
action, which fact eliminates such an inoculative method of
infection. It is as a mechanical carrier, briefly, that M.
(MS)
384
0. GOEDON H14WITT.
domestic a and such allies as H. canicular is, etc., though
to a less degree, may be responsible for the spread of in-
fectious disease of a bacillaiy nature, and an account will
now be given of the role which this insect plays in the
dissemination of certain diseases.1 Before doing so, however,
it should be pointed out that whereas in some of the diseases
the epidemiological evidence adduced in support of the trans-
ference of disease germs by flies is confirmed bacteriologically,
in others only the former evidence exists. Should neither
form of evidence be available in support of the idea that M.
domestica plays a part in the dissemination of the infection
of a particular disease, it is essential, nevertheless, that if
such a method of transference is possible the potency of this
insect should be realised. This potency is governed by such
factors as the presence of M. domestica; its access to the
infected or infective material, this being attractive to the
insect either because it is moist or because it will serve as
food for itself or its progeny ; and a certain power of resist-
ance for a short time against desiccation on the part of the
pathogenic organisms, although, as in the case of the typhoid
bacillus, the absence of this factor is not fatal to the idea, as
it may be overcome by the fact that the fly is able to take on
its appendages an amount sufficient to resist desiccation for a
short time. The last factor is the presence of suitable culture
media, such as certain foods, or moist sui'faces as the mouth,
eyes, or wounds, for the reception of the organisms which
have been carried on the body or appendages of the fly. If
these conditions are satisfied the possibility of M. domestica
or its allies playing a part in the transference of the infection
should be carefully considered, and this suggestive evidence
will be discussed in certain of the diseases which follow, in
addition to the epidemiological and bacteriological evidence.
1 Though it should he unnecessary, I wish to explain, as I have been
occasionally misunderstood by medical men and others, that M.
domestica is not regarded as being the cause of any disease, but as a
carrier of the infection.
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STEUCTUIIE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 385
1. Typhoid Fever.
Of all infectious diseases the conditions in this are most
favourable for the transference of infection by M. domestic a,
and it is no doubt on this account that the greatest attention
has been paid to the role of house-flies in the dissemination
of this disease. The chief favourable condition is that the
typhoid bacillus occurs in the stools of typhoid and incipient
typhoid cases. Human excrement attracts flies not only on
account of its moisture but as suitable food for the larvae.
The infected excrement is often accessible to flies, especially
in military camps, as will be shown shortly, and the flies also
frequent articles of food and not infrequently the moist lips of
man. Such are the conditions most suitable for the transfer-
ence of the bacilli, and it is on account of the frequent
coincidence of these conditions that flies can play, and have
played, such an important role in the dissemination of this
disease among communities, in spite of the fact that the
typhoid bacillus cannot survive desiccation, which I think is
an argument against its being carried by dust.
Epidemiological and other evidence. — There is a
very large amount of testimony given as to the role played
by flies in the spread of enteric in military stations and camps,
and especially during the two wars — the Spanish- American
and the Boer War. All the conditions most favourable for
the dissemination of the bacilli by flies were, and in many
military stations are still, present; open latrines or filth-
trenches accessible to flies on the one hand and on the other
the men's food within a short distance of the latrines. I
cannot do better than repeat the evidence in the words of the
witnesses and allow it to speak for itself.
Vaughan, a member of the U.S. Army Typhoid Commis-
sion of 1898, states
" My reasons for believing that flies were active in the dis-
semination of typhoid fever may be stated as follows :
1 Tn a paper, " Conclusions Reached after a Study of Typhoid Fever
among American Soldiers," read before the American Medical Asso-
ciation at Atlantic City, N.J., in 1900.
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386
C. GORDON HEWITT.
" (a) Flies swarmed over infected faecal matter in the pits and
then visited and fed upon the food prepared for the soldiers
in the mess-tents. In some instances where lime had recently
been sprinkled over the contents of the pits, flies with their
feet whitened with lime were seen walking over the food.
"b) Officers whose mess-tents were protected by screens
suffered proportionately less from typhoid fever than did
those whose tents were not so protected.
" (c) Typhoid fever gradually disappeared in the fall of
1898 with the approach of cold weather and the consequent
disabling of the fly.
" It is possible for the fly to carry the typhoid bacillus in
two ways. In the first place faecal matter containing the
typhoid germs may adhere to the fly and be mechanically
transported. In the second place, it is possible that the
typhoid bacillus may be carried in the digestive organs of the
fly and may be deposited with its excrement."
One of his conclusions was that infected water was not an
important factor in the dissemination of tj^phoid in the
national encampments of 1898, since only about one fifth of
the soldiers in the national encampments during the summer
of that year developed t}7phoid fever, whereas about 80 per
cent, of the total deaths were due to this disease. In the
latter connection Sternberg (1899) refers to a report of Dr.
Reed upon an epidemic in the Cuban "War, in which it was
stated that the epidemic was clearly not due to water
infection but was transferred from the infected stools of the
patients to the food by means of flies, the conditions being
especially favourable for this means of dissemination. Stern-
berg, as Surgeon-General of the U.S. Army, issued the follow-
ing instructions1 : " Sinks should be dug before a camp is
occupied or as soon after as practicable. The surface of the
faecal matter should be covered with fresh earth or quicklime
or ashes three times a day." I think that the instructions
of that ancient leader of men, Moses, who probably had
1 ' Circular No. 1 of the Surgeon- General of the U.S. Army,' April,
1898.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 387
experienced the effects of flies, were even better than these.
He said (Deut., Ch. xxiii, v. 12-13) : "Thou shalt have a
place also without the camp whither thou shalt go forth
abroad; and thou shalt have a paddle [or ' shovel '} among
thy weapons; and it shall be, when thousittest down abroad,
thou shalt dig therewith, and shalt turn back and cover that
which cometh from thee."
Sternberg is of the opinion that typhoid fever and camp
diarrhoea are frequently communicated to soldiers through
the agency of flies, "which swarm about faecal matter and
filth of all kinds deposited upon the ground or in shallow pits,
and directly convey infectious material attached to their feet
or contained in their excreta to the food which is exposed
while being prepared in the common kitchen, or while being
served in the mess-tent."
Veeder (1898), in referring to the conditions existing in the
camps of the Spanish- American war, says that in the latrine
trenches he saw " fascal matter fresh from the bowel and in
its most dangerous condition, covered with myriads of flies,
and at a short distance there was a tent, equally open to the
air, for dining and cooking. To say that the flies were busy
travelling back and from between these two places is putting
it mildly." Further, he says, " There is no doubt that air
and sunlight kill infection, if given time, but their very access
gives opportunity for the flies to do serious mischief as con-
veyers of fresh infection wherever they put their feet. In a
very few minutes they may load themselves with the dejec-
tions from a typhoid or dysenteric patient, not as yet sick
enough to be in hospital or under observation, and carry the
poison so taken up into the very midst of the food and water
ready for use at the next meal. There is no long and round-
about process involved. It is very plain and direct. Yet when
the thousands of lives are at stake in this way the danger
passes unnoticed, and the consequences are disastrous and
seem mysterious until attention is directed to the point ; then
it becomes simple enough in all conscience."
The Commission which investigated the outbreaks of
388
0. GORDON HEWITT.
enteric fever that occurred in 1898 in tlie United States
during tin's war came to the conclusion that " flies undoubtedly
served as carriers o£ the infection" under the conditions
which have already been described. Many other authorities
bear witness to the same facts.
In our own South African war, a year or two later, the
same conditions existed, and there was a very heavy loss of
life from enteric fever. Writing on the subject, Dunne
(1902) says: "The plague of flies which was present during
the epidemic of enteric at Bloemfontein in 1900 left a deep
impression on my mind, and, as far as I can ascertain from
published i-eports, on all who had experience on that occasion.
Nothing was more noticeable than the fall in the admissions
from enteric fever coincident with the killing off of the flies
on the advent of the cold nights of May and June. In July,
when I had occasion to visit Bloemfontein, the hospitals there
were half empty, and had practically become convalescent
camps."' A similar experience is related by Tooth (1901).
Referring to the role of flies he says: "As may be expected,
the conditions in these large camps were particularly favour-
able to the growth and multiplication of flies, which soon
became terrible pests. I was told by a resident in Bloem-
fontein that these insects were by no means a serious plague
in ordinary times, but that they came with the army. It
would be more correct to say that the normal number of flies
was increased owing to the large quantities of refuse upon
which they could feed and multiply. They were all over our
food, and the roofs of our tents were at times black with
them. It is not unreasonable to look upon flies as a very
possible agency in the spreading of the disease, not only
abroad but at home. It is a well-known fact that with the
first appearance of the frost entei-ic fever almost rapidly
disappears. ... It seems hardly credible that the almost
sudden cessation of an epidemic can be due to the effect of
cold upon the enteric bacilli only. But there can be no doubt
in the mind of anybody who has been living on the open
veldt, as Ave have for three or four months, that flies are ex-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-FLY. 389
tremely sensitive to the change of temperature, and that the
cold nights kill them off rapidly." In the discussion on this
paper Church stated that " many nurses told me that if one
went into a tent or ward in which the patients were suffering
fronra variety of diseases, one could tell at once which were
the typhoid patients by the way in which the flies clustered
about their mouths and eyes while in bed." It was further
stated in the discussion that where the Americans used quick-
lime in their latrines the cooks in the neighbouring kitchens
found that the food became covered with quicklime from the
flies which came from the latrines to the kitchens.
Dr. Tooth, in a letter to me, says : " I am afraid my written
remarks hardly express strongly enough the importance that
I attach to flies as a medium of spreading infection. Of course
I do not wish to under-rate the water side of the question,
but once get, by that means, enteric into a camp the flies, in
rny opinion, are quite capable of converting a sporadic incidence
into an epidemic. A pure water supply is an obvious necessity,
but the prompt destruction of refuse of every description is
eveiy bit as important."
Smith (1903), in speaking of his experiences in South
Africa, says that : " On visiting a deserted camp during the
recent campaign it was common to find half a dozen or so
open latrines containing a foetid mass of excreta and maggots."
Similar observations were made by Austen (1904), who, de-
scribing a latrine that had been left a short time undisturbed,
says : "A buzzing swarm of flies would suddenly arise from it
with a noise faintly suggestive of the bursting of a percussion
shrapnel shell. The latrine was certainly not more than one
hundred yards from the nearest tents, if so much, and at meal-
times men's mess-tins, etc., were always invaded by flies. A
tin of jam incautiously left open for a few minutes became a
seething mass of flies (chiefly Pycnosoma chloropyga
, Wied), completely covering the contents."
Howard (1900) referring to an American camp, where no
effort was made to cover the fasces in the latrines, says : " The
camp contained about 1200 men, and flies were extremely
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:.HH)
C. GORDON HEWITT.
numerous in and around the sinks. Eggs of Musca domes-
tica were seen in large clusters on the faeces, and in some
instances the patches were two inches wide and half an inch
in depth, resembling little patches of lime. Some of the sinks
were in a very dirty condition and had a very disagreeable
odour."
A few examples of the prevalence of conditions favouring the
dissemination of enteric by flies in permanent camps may be
noted. Cockerill (1905), in .describing camp conditions in
Bermuda, mentions kitchens within one hundred yards of the
latrines ; the shallow privy, seldom or never cleaned out, and
middens are found'which contain masses of filth swarming with
flies. He states that in. more recent years the period of greatest
incidence is in the summer, being chiefly due to flies and con-
taminated dust. Quill (1900), reporting on an outbreak of
enteric in the Boer camp in Ceylon, states : " During the
whole period that enteric fever was rife in the Boer camp
flies in that camp amounted to almost a plague, the military
camp being similarly infested, though to a less extent. The
outbreak in the Boer camp preceded that among the troops;
the two camps were adjacent, and the migration of the flies
from the one to the other easy." Weir, reporting on an out-
break of enteric fever in the barracks at Umbala, India,1 says
that most of the pans in the latrines were half or quite full,
and flies were very numerous in them and on the seats, which
latter were soiled by the excreta conveyed by the flies' legs.
The men stated that the plague of flies was so great that
in the morning they could hardly go to the latrines. He
found that the flies were carried from the latrines to the
barrack-rooms on the clothes of the men. This state of affairs
suggests another mode of infection, namely, per rectum.
As Smith has pointed out (I.e.) it is not improbable that
flies under these conditions may be inoculators of dysentery.
Aldridge (1907) gives some interesting statistics showing
the influence of the presence of breeding-places of flies. Flies
are found in greater numbers in mounted regiments thau in
1 ' Army Medical Department Report,' 1902, p. 207.
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 391
infantry, and he shows how this affects the incidence of enteric
fever. In the British Army in India, 1902-05, the ratios per
1000 per annum of cases admitted were : cavalry 41'1, and
infantry 15-5 ; and iu the U.S. Army were: cavalry 5*74,
and infantry 4*75. He states that : "A study of the incidence
of enteric fever shows that stations where there are no filth
trenches, or where they are a considerable distance from the
barracks, all have an admission-rate below the average, and
all but one less than half the average."
All these facts are equally applicable to the conditions in our
own towns and cities. Where the old conservancy methods are
used, such as pails and privy middens, the incidence of typhoid
fever is greater than in those places where the system of water
disposal has been adopted. I have examined the annual
reports of the medical officers of health of several large towns
where such conversions are being made, and they show a
falling-off of the typhoid fever-rate coincident with this
change. In Nottingham, for example,1 in the ten years 1 887—
1896, there was one case of typhoid fever for every 120 houses
that had pail-closets, one case for every 37 houses with privy
middens, and one case for every 558 houses with water-closets.
The last were scattered, and not confined to the prosperous
districts of the town.
One of the most important investigations on the relation
of flies to intestinal disease was that of Jackson (1907).
He investigated the sanitary condition of New York
harbour and found that in many places sewer outfalls had not
been carried below low-water mark, consequently solid matter
from the sewers was exposed on the shores, and that during
the summer months on and near the majority of the docks
in the city a large amount of human excreta was deposited.
This was found to be covered with flies. The report, consi-
dered as a mere catalogue, is a most severe indictment against
the insanitary condition of this great water front. By means
of spot-maps he shows that the cases of typhoid are thickest
1 " Typhoid Fever and the Pail System at Nottingham," ' Lancet,'
November 29th, 1902, p. 1489.
VOL. 54, PART 3. — NEW 8EKIES. 28
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392
C. GORDON HEWITT.
near the points found to be most insanitary. He shows, as
English investigators have also shown, how the curves of
fatal cases correspond with the temperature curves and with
the curves of the activity and prevalence of flies which were
obtained by actual counts. He also adduced bacteriological
evidence, and it is stated that one fly was found to be carrying
over one hundred thousand fajcal bacteria.
Bacteriological evidence. — In addition to the evidence
of Jackson, to which reference has been made, further proof
that flies are able to carry the typhoid bacillus has been
available for some years. Celli (1888) recovered the Bacillus
typhi abdominalis from the dejections of flies which had
been fed on cultures of the same, and he was able to prove
that they passed through the alimentary ti-act in a virulent
state by subsequent inoculation experiments. Ficker (1903)
found that when flies were fed upon typhoid cultures they
could contaminate objects upon which they rested. The
typhoid bacilli were present in the head a,nd on the wings
and legs of the fly five days after feeding, and in the alimen-
tary tract nine days after. Firth and Horrocks (1902), in
their experiments, took a small dish containing a rich emul-
sion in sugar made from a twenty-four-hour agar slope of
Bacillus typhosus recently obtained from an enteric stool
and rubbed up with fine soil. This was introduced with some
infected honey into a cage of flies together with sterile litmus
agar plates and dishes containing sterile broth, which were
placed at a short distance from the infected soil and honey.
Flies were seen to settle on the infected matter and on the
agar and broth. The agar plates and broth were removed
after a few days, and after incubation at 37° C. for twenty-
four hours colonies of Bacillus typhosus were found on
the agar plates and the bacillus was recovered from the
broth. In a further experiment the infected material was
dusted over with fine earth to represent superficially buried
dejecta, and the bacillus was isolated from agar plates upon
which the flies had subsequently walked, as in the former
experiment. They also found the bacillus on the heads, wings,
STRUCTURE, DEVELOPMENT, AND BIONOMICS OP HOUSE-PLY. 393
legs and bodies of flies which had been allowed to have access
to infected material. Hamilton (1903) recovered Bacillus
typhosus five times in eighteen experiments from flies caught
in two undrained privies, on the fences of two yards, on the
walls of two houses and in the room of an enteric fever
patient. A series of careful experiments were made by
Sellars1 in connection with Niven's investigations on the
relation of flies to infantile diarrhoea. Out of thirty-one
batches of house-flies carefully collected in sterilised traps in
several thickly populated districts in Manchester he found,
as a result of cultural and inoculatory experiments, that
bacteria having microscopical and cultural characters resem-
bling those of the Bacillus coli group were present in four
instances, but they did not belong to the same kind or
variety. Buchanan (1907) was unable to recover the bacilli
from flies taken from the enteric ward of the Glasgow Fever
Hospital. Flies were allowed to walk over a film of typhoid
stool and then ti'ansferred to the medium (Griinbaum and
Hume's modification of MacConkey's medium), and subse-
quently allowed to walk over a second and a third film of
medium. Few typhoid bacilli were recovered and none from
the second and third films. Sangree (1899) performed
somewhat similar experiments to those of Buchanan and re-
covered various bacilli in the tracks of the flies. This method
of transferring the flies immediately from the infected material
to the culture plate is not very satisfactory, as I have already
pointed out (1908), as it would be necessaiy for the flies to
be very peculiarly constructed not -to carry the bacilli. The
fly should be allowed some freedom before it has access to the
medium to simulate natural conditions. Experiments of this
kind were carried out in the summer of 1907 by Dr. M. B.
Arnold (superintendent of the Manchester Fever Hospital)
and myself. Flies were allowed to walk over a film of
typhoid stool and then were transferred to a wire cage, where
they remained for twenty-four hours with the opportunity
1 Recorded in the ' Report on the Health of the City of Manchester,.
1906,' by James Niven, pp. 86-96.
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394
C. GORDON HEWITT.
of cleaning themselves, after which they were allowed to walk
over the films of media. Although we were unable to recover
B. typhosus the px-esence of B. coli Avas demonstrated.
B. coli was also obtained from flies obtained on a public tip
upon which the contents of pail-closets had been emptied; the
presence of B. coli, however, may not necessarily indicate
recent contamination with human excrement. Aldridge (\.c.^
isolated a bacillus apparently belonging to the paratyphoid
group from flies caught in a barrack latrine in India during
an outbreak of enteric fever. In appearance and behaviour
to tests it was very similar to B. typhosus.
Although we are not certain yet as to the specific organism
or organisms which cause the intestinal disease known as
infantile or summer diarrhoea, which is so prevalent during
the summer months and is responsible for so great a mortality
among young children, I think we must consider the relation-
ship of M. domestica and its ally Homalomyia cani-
cularis to this disease epidemiologically similar to typhoid
fever.
2. Anthrax.
In considering the relation of flies to anthrax several facts
should be borne in mind. As early as the eighteenth century
it was believed that authrax might result from the bite of a
fly, and the idea has been used by Murger in his romance
'Le Sabot Rouge.' A very complete historical account of
this is given by Nuttall (1899). Most of the instances in
support of this belief, however, that flies may carry the
infection of anthrax, refer to biting flies. As I have already
pointed out, M. domestica and such of its allies as H.
canicularis, C. ery throcephala, C. vomitoria, and
Lucilia cassar are not biting or blood-sucking flies. The
nearest allies of M. domestica which suck blood in England
are S. calcitrans, Haamatobia stimulans Meigen, and
Lyperosia irritans L. ; the rest of the blood-sucking flies
which may be considered in this connection belong to the
family Tabanidaj, including the coinmon genera Has ma-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 395
lopota, Tabanus, and Chrysops. These biting and blood-
sucking- flies live upon the blood of living rather than dead
animals. But it is from the carcases and skins of animals
which have died of anthrax that infection is more likely to
be obtained, and I believe that such flies as the blow-flies
(Calliphora spp.), and sometimes M. domestica and
Lucilia caasar, which frequent flesh and the bodies of dead
animals for the purpose of depositing their eggs and for the
sake of the juices, are more likely to be concerned in the
carriage of the anthrax bacillus and the causation of malig-
nant pustule than are the blood-sucking flies. Consequently,
as M. domestica and its allies only are under consideration,
and for the sake of brevity, the relation to anthrax of the
non-bitingf flies onlv will be considered hei'e.
The earliest bacteriological evidence in support of this
belief was published by Raimbert (1869). He experimentally
proved that the house-fly and the meat-fly were able to carry
the anthrax bacillus, which he found on their probosces and
legs. In one experiment two meat-flies were placed from
twelve to twenty-four hours in a bell-jar with a dish of dried
anthrax blood. One guinea-pig was inoculated with a pro-
boscis, two wings and four legs of a fly, and another with a
wing and two legs. Both were dead at the end of sixty
hours, anthrax bacilli being found in their blood, spleen, and
heart. He concludes: "Les mouches qui se posent sur les
cadavres des animaux morts du Charbon sur les depouilles,
et s'en nourissent, ont la faculte de transporter les virus char-
bonneux depose sur la peau peut en ti-averser les differentes
couches." Davaine (1870) also carried out similar experi-
ments with C. vomitoria, which was able to carry the
anthrax bacillus. Bollinger (1874) found the bacilli in the
alimentary tract of flies that he had caught on the carcase
of a cow dead of anthrax. Buchanan (I.e.) placed C.
vomitoria under a bell-jar with the carcase of a guinea-pig
(deprived of skin and viscera) which had died of anthrax.
He then transferred them to agar medium and a second agnr
capsule, both of which subsequently showed a profuse growth
396
C. GORDON HEWITT.
of B. anthracis as one might expect. Specimens of M.
domestica were also given access to the carcase of an ox
which had died of anthrax; they all subsequently caused
growths of the anthrax bacillus on agar. I entirely agree
with Nuttall, who says: "It does seem high time, though,
after nearly a century and a half of discussion, to see what
would be the result of properly carried out experiments.
That ordinary flies (M. domestica and the like) may carry
about and deposit the bacillus of anthrax in their excrements,
or cause infection through their soiled exterior coining in
contact with wounded surfaces or food, may be accepted as
proven in view of the experimental evidence already pre-
sented."
3. Cholera.
One of the first to suggest that flies may disseminate the
cholera spirillum was Nicholas (1873), who, in an interesting
and prophetic letter, said : " In 1849, on an occasion of going
through the wards of the Malta Hospital, where a large
amount of Asiatic cholera was under treatment, my first
impression of the possibilty of the transfer of the disease by
flies was derived from the observation of the manner in which
these voracious creatures, pi*esent in great numbers, and
having equal access to the dejections and food of the patients,
gorged themselves indiscriminately, aud then disgorged
themselves on the food and drinking utensils. In 1850 the
' Superb/ in common with the rest of the Mediterranean
squadron, was at sea for nearly six months; during the
greater part of the time she had cholera on board. On
putting to sea the flies were in great force, but after a time
the flies gradually disappeared and the epidemic slowly sub-
sided. On going into Malta Harbour, but without com-
municating with the shore, the flies returned in greater
force, and the cholera also with increased violence. After
more cruising at sea the flies disappeared gradually, with the
subsidence of the disease. In the cholera years of 1854 and
1866 in this country the periods of occurrence and disappear-
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-ELY. 397
ance of the epidemics were coincident with the fly-season."
Buchanan (1897), in a description of a gaol epidemic of cholera
which occurred at Burdwan in June, 1896, states that swarms
of flies occurred about the prison, outside which there were a
number of huts containing cholera cases. Numbers of flies
were blown from the sides where the huts lay into the prison
enclosure, where they settled on the food of the prisoners.
Only those prisoners who were fed in the gaol enclosure
nearest the . huts acquired cholera, the others remaining
healthy.
Bacteriological evidence. — Maddox (1885) appears to
have been the first to conduct experiments with a view to
demonstrating the ability of flies to carry the cholera spirillum,
or, as it was then called, the " comma-bacillus." He fed the
flies C. vomitoria and Bristalis tenax (the "drone-fly")
on pure and impure cultures of the spirillum, and appears to
have found the motile spirillum in the f asces of the flies. He
concludes that these insects may act as disseminators of
cholera. During a cholera epidemic Tizzoni and Cattaui
(1886) showed experimentally that flies were able to carry the
" comma-bacillus " on their feet. They also obtained, in two
out of three experiments, the spirillum from cultures made
with flies from one of the cholera wards. Sawtchenko (1892)
made a number of careful experiments. Flies were fed on
bouillon culture of the cholera- spirillum, and to be certain
that the subsequent results should not be vitiated by the
presence of the spirillum on the exterior of the flies, he dis-
infected them externally and then dissected out the alimentary •
canal, with which he made cultures. In the case of flies
which had lived for forty-eight hours after feeding, the
second and third cultures represented pure cultures of the
cholera spirillum. Simmonds (1892) placed flies on a fresh
cholera intestine, and afterwards confined them from five to
forty-five minutes to a vessel in which the}'- could fly about.
Boll cultures were then made, and colonies of the cholera
spirillum were obtained after forty-eight hours. Colonies
were also obtained from a fly one and a half hours after having
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398
C. GORDON nEWITT.
access to a cholera intestine, and also from flies caught in a
cholera post-mortem room. Uffelmaun (1892) fed two flies on
liquefied cultures of the cholera spirillum, and after keeping
one of them for an hour in a glass he obtained 10,500
colonies from it by means of a roll culture ; from the other,
which was kept two hours under the glass, he obtained
twenty-five colonies. In a further experiment he placed one
of the two flies similarly infected with the spirillum in a glass
of sterilised milk, which it was allowed to drink. The milk
was then kept for sixteen hours at a temperature of 20-21° C,
after which it was shaken, and cultures were made from it;
one drop of milk yielded over one hundred colonies of the
spirillum. The other fly was allowed to touch with its pro-
boscis and feed upon a piece of juicy meat that was sub-
sequently scraped. From one half of the surface twenty
colonies, and from the other half one hundred colonies, of the
spirillum were obtained. These experiments show the danger
which may result if flies having access to a choWa patient, and
bearing the spirillum, have access also to the food. Macrae
(1894) records experiments in which boiled milk was exposed
in different parts of the gaol at Gaya in India, where cholera
and flies were prevalent. Not only did this milk become
infected, but the milk placed in the cowsheds also became
infected. The flies had access both to the cholera stools and
to such food as rice and milk.
These foregoing experiments prove beyond doubt the ability
of flies to carry the cholera spirillum, both internally and
externally, in a virulent condition, and to infect food.
4. Tuberculosis.
Although it may be considered to be hardly necessary to
introduce flies as a means of disseminating the tubercle
bacillus, it has, nevertheless, been proved experimentally
that they are able to carry the bacillus in a virulent condition.
As early as 1887 Spillman and Haushalter carried on experi-
ments in which they found the tubercle bacillus in large
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STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 399
numbers in the intestines of flies from a hospital ward, and
also in the dejections which occurred on the windows and
walls of the ward. Hoffmann (1886) also found tubercle
bacilli in the excreta of flies in the room where a patient had
died of tuberculosis, and he also found the bacilli in the
intestinal contents. One out of three guinea-pigs which were
inoculated with the intestines died ; two inoculations with the
excreta had no effect, which led him to believe that the bacilli
became less virulent in passing through the alimentary tract.
But Celli (1. c.) records experiments in which two rabbits
inoculated with the excreta of flies fed with tubercular sputum
developed the disease. Hay ward (1904) obtained tubercle
bacilli in ten out of sixteen cultures made from flies which
had been caught feeding on bottles containing tuberculous
sputum. Tubercle bacilli were also recovered from cultures
made from the faeces of flies which had fed in the same
manner, which apparently caused a kind of diarrhoea in the
flies, and they died from two to three days afterwards.
Faeces of flies fed on tubercular sputum were rubbed up in
sterile water and injected into the peritoneal cavity of guiuea-
pigs, which developed tuberculosis. Buchanan (I.e.) allowed
flies to walk over a film of tubercular sputum and then over
agar; a guinea-pig died of tuberculosis in thirty-six days by
inoculating it with the resulting culture.
5. Ophthalmia.
Flies have been suggested as playing an important part in
the spread of conjunctivitis, especially Egyptian ophthalmia,
and although, so far as I have been able to discover, we have
no bacteriological evidence in favour of the belief, the circum-
stantial evidence is sufficiently strong to warrant it.
In speaking of its occurrence at Biskra, Laveran (1880)
says that in the hot season the eyelids of the indigenous
children are covered with flies, to the attentions of which
they submit; in this way the infectious discharge is carried
on the legs and probosces of flies to the healthy children.
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400
C. GORDON HEWITT.
Dr. Andrew Balfour, of the Gordon College, Khartoum, m a
letter to me, says that the Koch-Weeks bacillus is generally
recognised as being the exciting cause of Egyptian ophthal-
mia. He says, " Ophthalmia is not nearly so common in the
Sudan as in Egypt, nor are flies so numerous ; doubtless the
two facts are associated." Dr. MacCallan, of the Egyptian
Department of Public Health, in answer to my inquiries, says
that acute ophthalmias are more liable to transmission by
flies than is trachoma. In his opinion the spread of the
latter is, to a comparatively small extent, through the agency
of flies, but it is mainly effected by direct contact of the
fingers, clothes, etc.
The Koch- Weeks bacillus Avas first seen by Koch (1883) in
Egypt in cases of acute catarrhal ophthalmia. He found that
two distinct diseases were referred to under the name ; in the
severe purulent form he found diplococci, which he identified
as very probably Gonococci; in the more catarrhal form he
found small bacilli in the pus-corpuscles. He ascribed the
propagation of the disease to flies, which were often seen
covering the faces of children. Axenfeld (1908) states that
"almost the only organisms occurring in acute epidemics
of catarrhal conjunctivitis are the Koch-Weeks bacillus
(perhaps also influenza bacillus), and the pneumococcus (in
Egypt the gonococcus also, rarely subtilis). Other
pathogenic conjunctival organisms1 only exceptionally occur."
And, further, "Gonococci and Koch-Weeks bacilli evi-
dently lose their power of causing a conjunctivitis very slowly
indeed, and are very independent of any disposition." His
statement that, "on account of their great virulence and the
marked susceptibility to them, a very small number suffices,"
is important in considering the relation of flies to the spread
of the disease, although, as he remarks, every infection does
not produce the disease. The fact that the Koch-Weeks
bacillus cannot resist dryness cannot be urged as an argument
1 In this connection lie states (p. 236) : " We can make the general
statement that the staphylococcus in the conjunctiva is not conta-
gious.'
(160)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 401
against the spvead of the infection by flies, or the same would
apply to the typhoid bacillus, whose carriage by flies is
proven. Axenfeld mentions L. Miiller and Lakah and Khouri
as advocating the view that flies may spread the infection
more readily. In view of the fact that, as the same author
states, " Koch- Weeks conjunctivitis is to be classed with the
most contagious infectious disease which we know of," it is
important that the role of flies should be fully recognised.
Notwithstanding the occurrence in this country of flies in less
numbers than in such countries as Egypt, it would be well to
bear in mind the probable influence of flies in cases of acute
conjunctivitis, such as those described by Stephenson (1897)
in our own country. The sole difference between the disease
in Egypt and here is, as Dr. Bishop Harman points out to me
in a letter, that " the symptoms produced (in- Egypt) are, from,
climate aud dirtiness of the subjects, more severe, and that
there is found a greater number of cases of gonorrbceal
disease than in England"; and, I would add, a far greater
number of flies. This disease is eminently suited for dissemi-
nation by flies, both on account of the accessibility of the
infectious matter in the form of a purulent discharge from
the eyes and on account of the flies5 habit of frequenting
the eyes.
6. Plague.
Although fleas are considered to be the chief agents in the
dissemination of the plague bacillus in spite of the fact that
the proof is not absolutely convincing, it is nevertheless
interesting, and certainly not unimportant, to refer to the
series of experiments of Nuttall (1897) on M. domestica.
In these experiments he conclusively proved that flies were
able to carry the plague bacillus, and that they subsequently
died of the disease. Flies were fed upon the crushed organs
of animals which had died of plague. Control flies were fed
in a similar manner on the organs of uninfected animals, and
the control experiments were kept under the same conditions.
(161)
402
C. GORDON HEWITT.
In two of the experiments the flies were all dead on the
seventh and eighth days respectively, at a temperature of
14° C. At higher temperatures he found that flies died more
rapidly. He was able to show that the flies contained the
bacilli in a virulent condition for about two days after they
had fed on infected organs ; this, and the fact that the infected
flies can live for several days, are extremely important from
the practical standpoint, as indicating that flies should neither
be allowed to have access to the bodies or excreta of cases of
plague, nor to the food.
7. Miscellanea.
There are on record a number of suggestions that flies may
be responsible for the dissemination of other diseases caused
by bacteria and other micro-organisms, and some account will
now be given of these and the experiments in support of such
beliefs.
If flies have access to wounds of an inflammatory and sup-
purative nature they are liable to transport the Staphylo-
cocci to other spots. Buchanan (1907) allowed M. domestica
to walk over a film of Staphylococcus pyogenes aureus
from an abscess, and afterwards over agar ; a mixed growth
resulted, in which S. pyogenes aureus predominated.
Celli (I.e.) records experiments which proved that S.
pyogenes aureus retains its virulence after passing
through the intestine of the fly.
In the experiments carried out in 1907 by my friend Dr.
M. B. Arnold and myself, he chose B. prodigiosus for
the purposes of the experiment, as it is easily recognisable
and not likely to be accidentally introduced. Flies which had
just emerged from the pupa3, and therefore not already con-
taminated with an extensive bacterial flora, were allowed to
walk over a film of the bacillus, after which they were con-
fined to sterile glass tubes. At varying periods they were
taken out and allowed to walk over the culture plates. Those
confined for over twelve hours retained the bacilli on their
(162)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 403
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404
C. GORDON HEWITT.
appendages and transferred them subsequently to the culture
media, but they were not recovered from those flies which
were kept in confinement for twenty-four hours ; a large
number of flies, however, were not used.
Dr. Kerr, of Morocco, in a paper on " Some Prevalent
Diseases in Morocco/5 read before the Glasgow Medico-
Chirurgical Society (December 7th, 1906), described epidemics
of Syphilis where, according to the author, the disease was
spread by flies which had been feeding upon the open sores
of a syphilitic patient.
Howard (1909) calls attention to an important investigation
carried on by Esten and Mason (1908) on the role which flies
play in the carriage of bacteria to milk. The flies were caught
by means of a sterile net'; they were then introduced into a
sterile bottle and shaken up in a known quantity of sterilised
water to wash the bacteria from their bodies and to simulate
the number of organisms that would come from a fly falling
into a quantity of milk. They summarised their results in the
table given on p. 403.
From that table it will be seen that the numbers of
bacteria carried by a single fly may range from 550 to
6,600,000, while the average number was about 1,222,000.
Commenting on these results, the authors state that " early in
the fly-season the numbers of bacteria on flies are compara-
tively large. The place where flies live also determines
largely the numbers that they carry." From these results the
importance of keeping flies away from milk and other food
will readily be seen.
VIII. Flies and Intestinal Myiasis.
The larvae of M. domestica and its allies are frequently
the cause of intestinal myiasis and diarrhoea in children. The
occurrence of the larvae in the human alimentary tract may be
accounted for in several ways. The flies may have deposited
the eggs on the lips or in the nostrils of the patient, or the
eggs may have been deposited on the food, subsequently
(164)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 405
passing uninjured either as eggs or as young larvae into the
alimentary tract owing to insufficient mastication. Or the
larvae may have entered per rectum, the eggs having been
deposited when the patient was visiting one of the old-style
privies where these flies, especially H. canicularis and
H. scalaris, frequently abound. These last two species are
frequently the cause of this intestinal trouble, and it is most
probable that the larvae enter per rectum.
Owing to the inability on the part of the observers to dis-
tinguish the different species of dipterous larvae we have
little information as to their occurrence in these cases.
Stephens (1905) records two cases. Two larvae were pro-
cured which were stated to have been passed per rectum ;
one was H. canicularis and the other is described as
M. corvina. The latter larva was stated to possess eight
lobes on the anterior spiracular processes which " distinguishes
these larvae from M. domestica, which has seven only." I
suspect this larva was M. domestica, which has six to eight
lobes on the anterior spiracular processes. Some years ago
a number of larvae which had been passed by a child Avere
sent to this laboratory, and I found that they were M. domes-
tica. In 1905 some eggs taken from the stool of a patient
suffering from diarrhoea were sent to me and on examination
they proved to be the eggs of C. ery throcephala. The
larvae of the small house-fly, H. canicularis, as I have
already mentioned, have occasionally been found in the stools
of patients.
In certain cases the larvae may wander from the mouth or
alimentary tract and get into the nasal passages or other
ducts, in which cases complications may ensue and result in
the death of the patient.
IX. Literature.
A few of the more important references included in the two previous
bibliographies are repeated here for the sake of convenience.
1909. Ainsworth, R. B.— "The House-fly as a Disease Carrier," ' Journ.
Roy. Army Med. Corps,' vol. xii, pp. 485-498.
(166)
406 C. GORDON HEWJTT.
1904. Aldridge, A. R. — " The Spread of the Infection of Enteric Fever
by Flies," ibid., vol. iii, pp. 649-651.
1907. "House-flies as Carriers of Enteric Fever Infection,"
ibid, vol. ix, pp. 558-571.
. 1904. Austen. E. E.— " The House-fly and Certain Allied Species as
Disseminators of Enteric Fever among Troops in the Field,"
ibid, vol. ii, pp. 651-668, 2 pis.
1908. Axenfeld, T.— 'The Bacteriology of the Eye' (Translated by
A. MacNab), London, 402 pp., 87 figs., 3 pis.
1901. Bachmetjew, P. — ' Experimentelle entomologische Studien. i.
Temperaturverhiiltnisse bei Insekten,' Leipzig, 160 pp.
1903. Balfour. A.—' Third Report of the Wellcome Research Labora-
tories, Gordon College, Khartoum,' pp. 218, 219.
1905. Banks, N. — " A Treatise on the Acarina or Mites," ' Proc. U.S.
Nat. Mas.,' vol. xxviii, pp. 1-114, 201 figs.
1858. Beclard, J. — " Influence de la lumiere sur les animaux," ' C.R. de
l'Acad. d. Sc.,' vol. lvi, pp. 441-453.
1898. Berg, C. — " Sobre los enemigos pequefios de la langosta peregrina
Schistocerca paranensis (Burm.)," 'Com. Mus. Buenos
Aires,' vol. i, pp. 25-30.
1887. Bigot, J. M. F. — " Dipteres nouveaux on pen connus," ' Bull. Soc.
Zool. France,' vol. xii, pp. 581-617.
1903. Bogdanow, E. A. — " Zehn Generationen der Fliegen (Musca
domestica) inveriindertenLebensbedingungen," ' Allg. Zeitschr.
f. Entom.,' vol. viii, pp. 265-267.
1874. Bollinger, O. — " Experimentelle Untersuchungen uber die Ent-
stehung des Milzbrandes," 46 Yersamml., d. ' D. Naturf. u.
Aerzte zu Wiesbaden,' September, 1873; and " Milzbrand," in von
Ziemssen's ' Handb. d. spec. Patol. u. Therapie,' vol. iii, pp. 457
and 482.
1871. Brefeld, O. — "Untersuchungen uber die Entwickelung der
Empusa muscse and E. radicans," ' Abh. d. Naturf. Gesellsch.
Halle.,' vol. xii, pp. 1-50, pis. 1-4.
1897. Buchanan, W. J.—" Cholera Diffusion and Flies," ' Indian Med.
Gaz.,' pp. 86, 87.
1907. Buchanan. R. M. — " The Carriage of Infection by Flies," 'Lancet,'
vol. clxxiii, pp. 216-218, 5 figs.
1861. Carter, H. J. — " On a Bi-sexual Nematoid Worm which Infests
the Common House-fly (Musca domestica) in Bombay," ' Ami.
Mag. Nat. Hist.,' ser. (3), vol. vii, pp. 29-33, 4 figs.
1888. Celli, A.—" Transmissibilita dei germi patogeni mediante le
STRUCTURE, DEVELOPMENT, AND BIONOMICS OF ROUS 15-PLV. 407
dejecioni delle Mosche." 'Bull. Soc. Lancisiana ospedali di Roma,'
fasc. 1 , p. 1.
1905. Cockerill, J. W.—" Report on the Prevalence of Enteric Fever in
Bermuda," with Tables and Diagrams, ' Journ. Roy. Army Med.
Corps,' vol. iv, pp. 762-796.
1855. Colin, F. — "Empusa uiuscse mid die Krankheit der Stuben-
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1870. Davaine, C. — " Etudes sur la contagion du charbon chez les
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1861. Diesing, K. M. — " Kleine helmintliologische Mittheilungen,"
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1872. Donhoff. — " Beitriige zuv Physiologie, I : Ueber das Verhalten
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724.
1797. Donovan, E. — ' Natural History of British Insects,' vol. vi, p. 84.
1902. Dunne, A. B. — " Typhoid Fever in South Africa ; its Cause and
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1908. Esten, W. M., and Mason, C. J.—*' Sources of Bacteria in Milk,"
' Bull. No. 51, Storrs Agric. Exp. Sta.,' Storrs, Conn., U.S.A.
1903. Ficker, M— " Typhus und Fliegen," ' Arch. f. Hygiene,' vol. xlvi,
pp. 274-282.
1902. Firth, R. H, and Horrocks, W. H.— " An Incpiiry into the
Influence of Soil, Fabrics, and Flies in the Dissemination of
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1906. Franklin, G. D. — " Some Observations on the Breeding Ground
of the Common House-fly," ' Indian Med. Gaz.,' vol. xli, p. 349.
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176-1. Geoffroy, E. L. — 'Histoire abrcgce des Insectes.' vol. ii, p. 624.
1879. Giard, A. " Deux esprces d'Entomophthora no\i vcaux pour la
flore francaise et In presence de la forme Tarichium sur une
Muscide," 'Bull. Scient. du Department du Nord,' si r. 2, second
year, No. 11, pp. 353-363.
1909. Godfrey, R. — " The False-scorpions of Scotland," 'Ann. Scot.
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VOL. 54, PART 3. — NEW SERIES. 29
(167)
408
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1883. Grassi, B.— '• Les nicfaits des Mdnches," 'Arch. ital. de biologie,'
vol. iv, pp. 205-228.
1908. Hamer, W. H. — " Nuisance from Flies," Report by the Medical
Officer presenting a report by Dr. Hamer. Medical Officer (General
Purposes), on the extent to which the fly nuisance is produced
in London by accumulations of offensive matter. 10 pp., 2 figs.,
3 diagrams. Printed for the London County Council (Public
Health Committee), London.
1908. Hamer, W. H.— " Nuisance from Flies," Report of the Medical
Officer of Health presenting a further report by Dr. Hamer,
Medical Officer (General Purposes), on the extent to which the fly
nuisance is produced in London by accumulations of offensive
matter. 6 pp., 4 diagrams. Printed for the London County
Council (Public Health Committee), London.
1904. Hayward. E. H.— " The Fly as a Carrier of Tuberculous Infec-
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1888. Hoffmann, E. — " Ueber die Verbreitung der Tubereulose durch
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•STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-ELY. 409
to Health by the Dissemina tion of Intestinal Disease through the
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1908. Kammerer, P. — " Regeneration des Dipterenflugels beim Imago,"
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Kaiserl. Gesundlieitsamte,' vol. xx, pp. 440-152, 7 figs.
L900. Quill, R. H. — "Report on an Outbreak of Enteric Fever at
Diyatalawa Camp, Ceylon, among the 2nd King's Royal Rifles,"
' Army Med. Dept. Report,' Appendix 4, p. 425.
1869. Raimbert, A. — " Reclrercbes experimentales sur la transmission
du Charbon par les mouclies," ' C.R. Ac. Sci. Paris,' vol. lxix, pp.
805-812.
1905. Rogers, L. — " Tlie Conditions affecting the development of
Flagellated organisms from Leishman bodies and their bearing
on the probable mode of infection," 'Lancet,' June 3rd, 1905,
pp. 1484-1487.
1899. Sangree, E. B. — " Flies and Typhoid Fever," ' New York Med.
Record,' vol. lv, pp. 88-89, 4 figs.
1802. Sawtckenko, J. G. — "Le role des mouches dans la propagation de
l'epidcinic cholcrique," ' Yratch,' St. Petersburg. (Reviewed in
' Ann. de l'lnstitut Pasteur, vol. vii, p. 222.)
1892. Simmonds, M. — " Fliegen imd Choleraiibertragen," ' Dents ch.
med. Wochenschr.,' No. 41, p. 931.
1903. Smith, F. — " Municipal Sewage," 1 Joum. Trop. Med.,' vol. vi,
p. 285.
1887. Spillmann and Haushalter.- — " Dissemination du bacille de la
tuberculose par les mouches," 'C.R. Ac. Sci.,' vol. cv, pp. 352-
353.
1878. Stein, F. R. — " Der Organismus des Infusionsthiere, iii, Abthei-
ltmg — Die Naturgeschichte des Flagellaten oder Geisselin-
fiisiorien," 154 pp., 24 pis., Leipzig.
1905. Stephens, J. W. W— " Two Cases of Intestinal Myiasis," 'Thomp-
son Yates and Johnstone Laboratories Report,' vol. vi, part i.
pp. 119-121.
L897. Stephenson, S. — "Report on the Prevalence of Ophthalmia in the
Metropolitan Poor-Law Schools," ' Blue-Book,' October 2nd.
1 897. (Reviewed in ' Lancet,' October 16th, pp. 090, 991.)
1899. Sternberg, G. M.— " Sanitary Lessons of the War," ' Philad. Med.
Joum.,' June 10th and 17th, 1S00.
1888. Thaxter, R— "The Entomophthorese of the United States,"
'Mem. Boston Hoc. Nat. Hist,,' vol. iv. pp. 133-201, pis. 14-21.
L886. Tizzoni, G., and J. Cattani. — " Untersuchungen iiber Cholera,"
' Centralbl. £. d. med. Wissench. Berlin,' vol. xxiv, pp. 769-771.
(171)
412
0. GORDON HEWITT.
1900. Tooth, H. H. — " Enteric Fever in the Army in South Africa."
' Brit. Med. Joum.,' November 10th, 1900.
1901. " Some Personal Experiences of the Epidemic of Enteric
Fever among the Troops in South Africa, in the Orange River
Colony." ' Trans. Olin. Soc.,' vol. xxxiv, 64 pp.
1892. Uffelmann, J. — "Beitriige zur Biologie der Oholerabaoillus,"
' Berl. klin. Wochenschr.,' 1892, pp. 1213-1214.
1898. Veeder, M. A. — " Flies as Spreaders of Disease in Camp," ' New
York Med. Record,' vol. liv, September 17th, p. 429.
1856. Walker, F. — ' Insecta Sanndersiana, i, Diptera,' p. 345.
1908. Werner, H. — " Uber eine eingeisselige Flagellatcnform im Darm
der Stubenfliege," ' Arch, f . Protistenk.,' vol. xiii, pp. 19-22, 2 pis.
1881. Winter, G.— " Zwei neue Entomophthoreen," 'Bot. Centralbl.,'
vol. v, p. 62.
X. Appendix.
On the Breeding of M. dotnestica during the
Winter Months.
In the account that I gave of the breeding habits of M.
doraestica in the second part of this monograph, it was
stated (p. 503) that the experiments and observations pointed
to the fact that, in the presence of suitable larval food, such
as excremental matter or decaying and fermenting food
materials in a moist and warm condition, the female flies
would lay their eggs and the larvae would develop if the
temperature of the air was sufficiently high for the prolonged
activity of the flies. Flies are sometimes found under these
conditions in warm restaurants and kitchens, stables, and
cowsheds, and under these conditions are able to breed during
the winter months. I am pleased to find that my own observa-
tions and those of Griffith (there referred to) as to the ability of
M.domestica to breed during the winter months has been
confirmed by Jepson1 during the past winter.
Flies were caught in February (1909 J in the bakehouse of
1 In " Reports to the Local Government Board on Public Health and
Medical S\ibjects (New Series, No. 5). Preliminary Reports on Flies as
Carriers of Infection. No. 3. Mr. Jepson's Report on the Breeding of
the Common House-Fly during the Winter Months," pp. 5-8, 1909.
(172)
STRUCTURE, DEVELOPMENT, AND BIONOMICS OE HOUSE-FLY. 413
one of the colleges (Cambridge), and were transferred to a
small experimental greenhouse in the laboratory where the
temperature was from 65° F. in the morning to 75° F. in the
evening. The flies were allowed to oviposit in moist bread in
which the process of fermentation had begun. He found
that the times for the developmental stages approxi-
mately agreed with those obtained by me at about the same
temperature, and that the whole development was completed in
about three weeks. At an average temperature of 70° F. the
eggs were all hatched in twenty-four hours. The first larval
stage lasted thirty-six hours, the second larval stage four
days, and the third stage was complete in five and a half
days; the whole larval period, therefore, occupied eleven
days. The average period occupied in the pupal stage was
ten days ; some pupse incubated at a temperature of 77° F.
hatched in three days.
It may be stated now, therefore, without fear of contra-
diction, that flies are able to breed during the winter months,
if the necessary conditions of food, temperature, and moisture
are present. It is probably from these winter flies that the
early summer flies are produced, as I have previously sug-
gested.
Corrigendum.
My attention has been very kindly called by Prof. W. A.
Riley to a slight mistake that I have made in my account of
the venation of the wing (Part I, p. 412). By an oversight
I have termed transverse nervures the two small veins
m.cu. (medio-cubital) and cu.a. (cubito-anal) . These are
really parts of the original longitudinal veins M. 3 and Cu. 2.
A study of such a series of dipterous wings as those figured
by Comstock in the papers there quoted (Comstock and
Needham, 1898), or in his ( Manual for the Study of Ento-
mology,' will show that these apparent transverse or cross-
veins are morphologically equivalent to branches of the
primary veins.
The University ;
Manchester.
(178)
414
C. (iOUHON HEWITT.
EXPLANATION OF PLATE 22,
Illustrating Dr. 0. Gordon Hewitt's paper on "The Structure,
Development, and Bionomics of the House-fly, Musen
domestica, Linn. Part III. The Bionomics, Allies,
Parasites, and the Relations of M. domestic^ to
Human Disease."
Fig. L — Mature larva of Homalomyia canicularis, L. x 17.
a.sp. Anterior spivaculav processes, p.sp. Posterior spiracular apertures.
Fig. 2.— Posterior end of mature larva of Anthomyia radicum
Mg. an. Anns.
Pig. 3.— Anterior spiracular process of mature larva of A. radicum.
Fig. 4.— Head of Stomoxys calcitrans. L. ; left lateral aspect.
Fig. 5. — Posterior end of mature larva of S. calcitrans.
Pig. (). — Posterior spiracle of the same, enlarged,
Fig. 7.— Posterior spiracle of mature larva of Mnsca domestica.
Fig. 8. — Posterior spiracles of first larval stage of Oalliphora
erythrocephala, Mg.
Fi^. !)- — Posterior spiracles of second larval singe of 0. ery thro -
cepha la.
Fig. 10. — Posterior spiracle of mature larva of 0. erythrocephala.
Fin'. 11. —Anterior spiracular process of mature larva of 0. erythro-
cephala.
Fig. 12. — Posterior end of mature larva of C. erythrocephala.
Fig. 13. — C hemes no do s us. Schr. x 30.
Pig. 14. — Thoi'aco-abdominal region of Homalomyia canicu-
laris, ? . showing Gamasids attached to the ventral side of the abdomen.
Fi^'- 15; — Longitudinal (sagittal) section of abdomen of M. domestica,
which has been killed by Bmpusa niuscte, showing the felt work of
fungal hyphse filling the inside of the abdominal cavity and the pro-
duction of conidia in the intersegmental regions. X 12. c. Conidio-
phores producing conidia. /. Fungal hyphas.
Fig. lfi. — Four conidiophores showing the formation of conidia (c).
X 100 (approx.).
Fig. 17.— Conidium of Empusa muscse. X 400. o.g. Oil globule.
Fig. 18. — Habronema muscse (Carter). Adult but immature
specimen. X 85. (j.a. Genito-anal aperture.
Fig. 1^. — Candid end of Habronema musca3. x 360.
Fig. 20. — Tarsal joints of one of posterior pair of legs of Miisca
domestica. Lateral aspect, to show densely setaceous character.
174
XIII. APPENDIX A.
FTJETHEE OBSEEYATIONS OX THE DISSEMINA-
TION OF BACTEEIAL AND OTHEE OEGANISMS
BY MUSGA D0MEST1CA.
I. The Eelation of Elies to Summer Diakkhcea of
Infants.
Nash was one of the first medical observers to call
attention (in 1902) to the remarkable coincidence between
the abundance of flies and the prevalence of this serious
infantile disease. In the years 1902 and 1903 the summers
were wet and therefore unfavourable to the breeding and
activity of M. domestica, and in these years the diarrhceal
diseases were less prevalent and the infantile mortality rate
was considerably below the average. He suggested (1903),
in a paper read before the Epidemiological Society of London
in January, 1903, that flies carried the infective material
from all kinds of filth to the food supplies and were
responsible for the spread of this disease and supported his
contention with a further instance, namely, that " in the
early part of September, 1902, flies became prevalent, and
co-incidentally diarrhoea, which had hitherto been conspi-
cuous by its absence, caused thirteen deaths in Southend.
Then came a spell of cold weather; the flies rapidly
diminished in number, and no further deaths from diarrhoea
were recorded " (1905). In 1904, by means of a "spot map,"
he found that the great majority of deaths from diarrhoea
occurred in the proximity of brick fields in which were
daily deposited some thirty tons of house refuse, an admir-
able breeding place for this insect. He has shown the actual
175
APPENDIX A
danger Avhich exists in flies carrying bacterial organisms to
milk as many other investigators have shown, and the
danger resulting from the coincident occurrence of uncovered
milk and infected flies is too obvious to need emphasis.
"While one regrets that he should feel almost lost, as he
states, in the crowd which proclaims far and wide the
relation between summer diarrhoea and flies when he had
previously felt like one crying in the wilderness (1909, p.
154), it must be acknowledged that Nash did great service
in making this fact more widely known when there was so
little inclination on the part of medical men to believe it.
The great difficulty with which we are faced in discussing
the question of the relation of flies to the prevalence of
summer diarrhoea is that it has not been proved to the
satisfaction of most investigators what the specific patho-
genic organism is, or perhaps there are associated organisms.
Morgan (1906-7) isolated a bacillus which he designated
" No. 1," and which appears to be an important factor in
the causation of the disease. In a further paper Morgan
and Ledingham (1909) give a more complete account of
their researches on Morgan's bacillus which belongs to the
non-lactose fermenting group, to which group all the
pathogenic bacteria inducing affections of the intestinal
tract belong, namely, the typhoid and paratyphoid bacilli,
the dysentery and food-poisoning organisms. In 1905, 58
cases of infantile diarrhoea were examined and Morgan's
bacillus was found in 48'2 per cent. ; in 1906, in 54 cases it
was found in 55-8 per cent.; in 1907, 191 cases were
examined and it occurred in 16"2 per cent., and in 1908 it
occurred in 53 per cent, of the cases, numbering 166, that
were examined. It was found that rats and monkeys were
susceptible to infection by feeding and that they succumbed
after a period of diarrhoea. One of the most interesting and
highly suggestive results of the research was the discovery
of Morgan's bacillus in flies. " Batches of flies came for
APPENDIX A
176
examination from infected and uninfected houses in
Paddington and from a country house situated many miles
from London, where no cases of diarrhoea had occurred, at
any rate within a radius of two miles. The flies were killed
with ether vapour and crushed with a sterile rod in peptone
broth. The result was that Morgan's bacillus was isolated
from nine of the thirty-six batches from infected houses and
from one of the thirty-two batches from uninfected houses.
It was also got in five out of twenty-four batches from the
country house." Dr. Morgan in the course of a letter to
me says : " I certainly think they are carriers of summer
diarrhoea, and the variety I especially suspect of doing this
is the Musca domestica."
Hamer in his first report (1908) points out a difficulty in
the way of accepting this relation of flies to summer diar-
rhoea. He states : " It should be pointed out that there are
certain difficulties in the way of accepting the thesis that
the correspondence exhibited in the curves [he refers to the
fly curve and diarrhoea curve] affords reason for concluding
that flies and summer diarrhoea stand to one another in
relation of cause and effect. At the commencement of the
hot summer weeks, when the number of flies has begun to
show marked increase, the diarrhoea curve is rapidly rising.
After some weeks the number of flies reaches the maximum,
and then diminishes, and so, in almost precise correspon-
dence, does the amount of diarrhoea. A period is later
reached, towards the close of the hot weeks, at which the
number of flies is still as markedly excessive as at the
earlier period when the amount of diarrhoea was increasing,
but at the later period the amount of diarrhoea is declining ;
it even anticipates decline in the number of flies. If the fly
is to be regarded as the carrier of the organism which
causes diarrhoea, it might perhaps have been anticipated that
at the later period — the number of flies still being excessive
and infective material being then presumably more widely
177
APPENDIX A
distributed than ever before — the amount of diarrhoea,
instead of showing early and rapid decline, would still be
increasing. It would almost appear that the advocate of the
' fly-borne diarrhoea hypothesis ' must necessarily fall back
in support of his theory upon the hypothetical organism,
conveyed by the fly, which he may claim is affected by
temperature in such a way as to bring about correspondence
between the diarrhoea curve and the fly curve. The very
closeness of the correspondence between these two curves
may indeed from this point of view be thought of as
constituting a difficulty rather than a point in favour of the
hypothesis that summer diarrhoea is caused by flies." [The
italics are mine. — C. Gr. H.] No one, I think, would argue
this. What is argued is that there are excellent grounds
for believing that flies carry the infective organism or
organisms of summer diarrhoea.
Niven (1904) suggested that the explanation of the falling
off of the diarrhoea curve while the number of flies still
remain large might be due to the exhaustion of susceptible
material.
The one point which does not appear to be considered and
which, I think, will explain this seeming objection is the
great susceptibility of flies to changes of temperature, which
fact all who have studied closely the habits of M. domestica
and its allies will admit. When the temperature falls, flies
become more sluggish and retire more into the shelter of
houses and other buildings, although their numbers may
still be considerable. It is necessary, therefore, to study the
temperature curve in addition to the fly and diarrhoea curves.
If this is done, it is usually found that the fall in the
number of flies is preceded by a fall in the temperature and
that these two curves are associated closely, that is, the
numerical activity of the flies— since the numbers caught are
more indicative of their numerical activity than of their
numerical occurrence— is dependent upon the temperature,
APPENDIX A
178
and also, I have found, on the state of the weather and sky.
If the flies therefore become less active, they will be less
liable to transmit the organisms causing summer diarrhoea,
and although the numbers caught in the houses may exceed
in numbers those caught earlier in the season when the
diarrhoea curve was rising, those which are very active will
be less in number and consequently instead of increasing,
the diarrhoea curve begins to fall. The dissemination of
summer diarrhoea is brought about chiefly owing to the
activity of the flies outside the houses as well as inside. A
fall in temperature or a spell of dull weather decreases
considerably this outside activity and will therefore cause a
decline in the number of diarrhoea cases. The number of
cases of diarrhoea is dependent on the activity of the flies
and this is dependent on climatic conditions, chief of which
is temperature. Considered in the light of these facts this
seeming difficulty is not an argument against the idea that
we hold on the relation of flies to summer diarrhoea, hut
rather one in support of it.
II. Bacteria and Fungal Spores carried by Musca
DOMESTICA.
In the summer of 1908 my friend Mr. H. T. Giissow,
Dominion Botanist of Canada, made three extremely inter-
esting and instructive experiments with a view to discovering
the kinds of organisms which the house-fly may normally
carry, and he has kindly allowed me to give his results,
hitherto unpublished, here.
Experiment No. 1.
A fly was caught in his living room (Norwood, London)
at 10 a.m. on May 4th and allowed to walk over nutrient
agar-agar in a Petri dish; the necessary precautions being
taken to prevent extraneous infection of the medium. The
179
APPENDIX A
Petri dish was placed in an incubator and kept at 28° — 30°C.
At 6 p.m. on the same day there were plain indications of
colonies forming but they were too small to allow a separation
count.
May 5th, 10 a.m. — 7 colonies of Bacteria and 4 of Fungi
showing.
6th, 10 a.m. — 16 colonies of Bacteria and 5 of Fungi
showing.
,, 7th, 10 a.m. — 23 colonies of Bacteria and 6 of Fungi
showing.
,, 8th, 10 a.m. — 30 colonies of Bacteria and 6 of Fungi
showing.
That is, in 96 hours, 30 colonies of Bacteria and 6 colonies
of Fungi were observed.
The fungi were examined and identified as follows : —
2 colonies of Saccharomyces sp.
2 , , ,, Penicillium glaucum.
1 colony ,, Aspergillus niger.
1 ,, ,, Cladosporium herbarum.
The bacteria were removed in the ordinary manner and
were sub-cultured, plated out and identified as follows : ■ —
Micrococcus urece
Bacillus subtilis
Bacillus coli commune
Sarcina lutea
Stained by Gram
Not stained by Gram
2 colonies.
7
11
9
3
5
Experiment No. 2.
A fly was caught at 11.30 a.m. on May 4th out of doors
on Central J I ill, Norwood, London, and was allowed to walk
over nutrient agar-agar at 12 o'clock noon.
APPENDIX A
180
May 4th, 6 p.m. — Colonies were plainly forming.
,, 5th, 10 a.m. — 13 colonies of Bacteria and 6 colonies of
Fungi.
,, 6th, 10 a.m. — 21 colonies of Bacteria and 7 colonies of
Fungi.
,, 7th, 10 a.m. — 39 colonies of Bacteria and 7 colonies of
Fungi.
8th, 10 a.m. — 46 colonies of Bacteria and 7 colonies of
Fungi.
That is, in 94 hours, 46 colonies of Bacteria and 7 colonies
of Fungi were obtained from this fly No. 2. The fungi
were identified as follows : — ■
2 colonies of Macrosporium sp.
3 ,, ,, Penicillium glaucum.
1 colony ,, Cladosporium herbarum.
1 ,, ,, Fusarum roseum.
The bacteria after being sub-cultured and plated out were
identified as : —
Bacillus tumescens
Micrococcus pyogenes aureus
Sarcina lutea
Sarcina ventriculi
Bacillus amylobacter
Acid fast bacillus...
Stained by gram ...
Not stained by gram
18
9
2
1
4
1
4
colonies.
colony,
colonies,
colony,
colonies.
Experiment No. 3.
This experiment was perhaps the most interesting of the
three as the fly was captured at 10.30 a.m. on May 4th on
a dust bin (Norwood, London), a situation in which flies are
frequently found. It was allowed to walk over the surface
of nutrient agar-agar.
181
APPENDIX A
May 4tli, 6 p.m. — Signs of colonies observed.
5th, 10 a.m. — 18 colonies of -Bacteria and 7 colonies of
Fungi.
,, 6th, 10 a.m. — 58 colonies of Bacteria and 9 colonies of
Fungi.
,, 7th, 10 a.m.— 113 colonies of Bacteria and 10 colonies of
Fungi.
,, 8th, 10 a.m. — 116 colonies of Bacterid and 10 colonies of
Fungi.
That is, after 95^ hours, 116 colonies of Bacteria and 10
colonies of Fungi were obtained from this single fly. The
fungi were identified as : —
Penicillium glaucum 4 colonies.
Eurotium sp 1 colony.
Saccharomyces sp 2 colonies.
Fusarium roseum 1 colony.
Aspergillus nigcr 1 ,,
Mucor racemosa .. 1 ,,
The bacteria after having been sub-cultured and plated
out were identified as : —
Bacillus coli commune ... 34 colonies.
Bacillus subtilis 16 ,,
Bacillus tumescens 8 ,,
Bacillus lactis acidi 4 , ,
Sarcina lutea 12
Sarcina ventriculi 2 ,,
Micrococcus pyogenes aureus 21 ,,
Micrococcus urece 11 >>
Acid fast bacilli 2 ,,
Bacilli stained by gram ... 4 ,,
Bacilli not stained by gram 2 ,,
*
APPENDIX A 182
The extremely large number and preponderance of bacilli
carried by this fly No. 3 shows very strikingly the infection
which a fly frequenting 'such miscellaneous household refuse
as is contained in the average household dustbin and the
results of such careful experiments^ as those which are
recorded aboA^e demonstrate clearly not only that flies
normally carry about the spores of fungi and bacteria and
the extra-infection which they obtain by frequenting refuse,
but also their liability to carry and disseminate such, bacteria,
pathogenic and non-pathogenic, with which they may come
into contact in their wanderings. Such a demonstration as
to their ability to transfer non-pathogenic, putrefactive, or
pathogenic organisms renders further comment unnecessary.
III. Flies and Milk.
An instructive example of the influence of flies and milk
in the dissemination of typhoid fever is communicated by
Taylor (Colorado State Board of Health, U.S.A.) to the New
York Merchants' Association. He says : " In the city of
Denver we had a very sad as well as a plain demonstration
of the transmission of typhoid fever by flies and milk.
Early in August of this year the wife of a dairyman was
taken with typhoid fever, remaining at home about three
weeks before her removal to the hospital, August 28th.
During the first two weeks in September we received reports
of numerous cases of typhoid fever in the northern portion
of Denver, and upon investigation found that all these cases
had been securing th'eir milk from this dairy. An inspection
of the dairy was then made, and in addition to learning of
the illness of the dairyman's wife, we also found the dairy-
man himself suffering with a mild case of typhoid fever, but
still up and delivering milk. The water supply of this
dairy was fairly good. However, we found that the stools of
183
APPENDIX B
both the wife and husband had been deposited in an open
privy vault located thirty-five feet from the milk-house,
which was unscreened and open to flies. The gelatine
culture exposed for thirty minutes in the rear of the privy
vault and in the milk-house among the milk-cans gave
numerous colonies of typhoid bacilli, as well as colon bacilli
and the ordinary germ-life. The source of infection in the
dairyman's wife's case is unknown, but I am positive that
in all the cases that occurred on this milk route the infection
was due to bacilli carried from this vault by flies and
deposited upon the milk-cans, separator and utensils in the
milk-house, thereby contaminating the milk. The dairyman
supplied milk to 143 customers. Fifty-five cases of typhoid
fever occurred, and six deaths resulted therefrom." (From
" The House-fly at the Bar Indictment Guilty or Not
Guilty?" The Merchants' Association of New York. April,
1909, 48 pp.)
IV. Flies in Military Camps.
Dutton (1909) gives an interesting figure to demonstrate
the manner in which flies would be carried from sources of
typhoid infection (Division Hospitals and Latrines) in the
Camps of the United States Army at Fernandina and Tampa
to different parts of these camps. He states that Sergeant
Brady, who was stricken with typhoid fever at Fernandina,
mentioned to him that the lime used about the latrines and
garbage dumps was carried by flies to the food which was
being used in the camps.
XIV. APPENDIX B.
ADDITIONAL OBSEEVATIONS ON THE BREEDING-
HABITS OF MUSCA DOMESTIC A.
Since the third part of this monograph was written and
sent to press (July, 1908) I have collected further data as to
APPENDIX B
184
the substances in which they are able to breed, and to make
this account of the bionomics of Musca domestica as complete
as possible I am giving a brief account of them here.
In the collection of Diptera in the Division of Entomology
of the Department of Agriculture of Canada, I found
specimens of M. domestica which had been reared in ger-
minating wheat. The parent fly had no doubt chosen such
material as an admirable nidus for her progeny, as
germinating wheat, on account iof the fermentation taking
place in the same, forms an excellent substance for the
development of the larvae.
Allied to this observation are some experiments by Nash
(1909) in which he reared flies in fermenting bread, and
his methods were followed by Jepson in the experiments
already recorded. Nash also mentions (I.e.) that he has
succeeded in rearing them on pear, potato, banana skins,
boiled rice and old paper, but he experienced the same
failure as I did in attempting to breed them in cheese. He
records an interesting observation of Austen's which the
latter made in 1908. Austen found the larvae of M. domestica
in rubber which was suspended in a drying room at a
temperature of 100oI\ They were apparently full grown
and the circumstances indicated that they could not have
been more than three days in developing from the egg stage,
which indicated a rapid growth at this exceedingly high
temperature.
The foregoing observations taken in conjunction with those
of my own and other investigators given in the second part
of this monograph emphasise the fact that M. domestica is
able to breed in practically any decaying animal or vegetable
substance or excrement, especially if it is in a state of fer~
mentation and if there is a sufficient amount of moisture
and a suitable temperature, the last two conditions being
concomitant with fermentation.
185
XV. APPENDIX C.
PREVENTIVE MEASURES.
In 1897 Howard conducted a series of experiments with a
view to discovering an insecticidal substance which could be
used for the destruction of the larvae in the heaps of manure
in which they were breeding. He found that both lime and
gas lime were not efficacious. In an experiment in which
8 lbs. of horse manure containing larvae were treated with a
pint of kerosene, which was washed down into the manure
with water, it was found that all the larvae were killed. He
also found that by treating 8 lbs. of well-infested horse
manure with one pound of chloride of lime all the larva?
were killed, but the results were not satisfactory when a
quarter of the quantity of chloride of lime was used. On
experimenting with the kerosene treatment on a large scale
he found that it was not only laborious but also not entirely
successful, as is sometimes the case in the practical applica-
tion on a large scale of successful experimental methods. He
therefore devised another method of treating the horse
manure of stables. A chamber six feet by eight feet was
built in the corner of the stable with which it communicated
by means of a door; it was provided also with a window
furnished with a wire screen. The manure was thrown into
the chamber -every morning and a small shovelful of chloride
of lime scattered over it. At the end of ten days or a
fortnight the manure was removed through an open door
and carted away. The experiment was carried out in the
stable of the U.S. Department of Agriculture and a marked
decrease in the number of flies was observed.
In France residuum oil has been proposed as a suitable
substance for the destruction of the eggs and larvae in privies
ami cesspools. Of such insecticidal substances as have been
practically tested chloride of lime is undoubtedly the cheapest
and most efficacious. The best preventive measure, however,
APPENDIX D
ISO
which can be suggested as a result of the study of the
breeding habits is the periodical and regular removal of the
horse-manure at intervals not exceeding seven days. Tbe
use of insecticidal substances could not be satisfactorily
supervised, apart from the fact that there would be a great
risk of their not being wholly efficacious. The periodic
removal of the breeding places could be regulated. The
same method of procedure should also be adopted with
respect to the other breeding places such as kitchen refuse,
the keeping of which in perfectly closed receptacles should
be enforced as also the periodic emptying of the same within
seven days in the summer months. The substitution of
modern methods of water-carriage for the older conservancy
methods in privies, etc., will abolish a very common breeding
place and also a common source of infection. The destruc-
tion of refuse by public and other destructors instead of its
deposition on £ tips ' would decrease a common breeding
place. In a few words, the prohibition of the exposure and
the frequent periodic removal of the substances in which
Musca domestica has been shown to breed are the methods to
be employed to bring about its numerical reduction and a
diminution of its liability to bacterial infection.
In addition, such substances as milk, sugar, etc., to Avhich
flies are attracted, should be kept covered, and flies should
not be allowed to come into contact with any food substances
nor with the faces of young children or persons who are ill
but should be prevented from doing so by means of muslin
or other screens.
XVI. APPENDIX D.
A FURTHER PARASITE OP THE HOUSE-FLY
(MUSCA DOMESTICA).
In a series of papers, of which the first only has appeared,
Girault and Sanders (1909) are describing a number of
187
APPENDIX D
hyruenopterous parasites reared from Musca domestica. All
the parasites belong to the family Pteromalidae and the
three generic forms which predominated were Spalangia,
Latreille; Musciclifurax, Girault and Sanders; and Nasonia,
Ashmead. One species of the last genus only is described in
the first paper of the series, namely, Nasonia brevicornis,
Ashmead.
Nasonia brevicornis , Ashmead.
It was found that this small parasite which is very
sluggish in its movements attacked the larvae and pupa? of
Musca domestica in confinement. A number of males and
females were reared from the pupae of M. domestica. The
female of N. brevicornis varies in length from 1 mm. to 2'30
mm., and is of a metallic dark brassy green colour, the eyes
are garnet. The male is about one-third smaller than the
female, varying in length from 0"60 mm. to 2'00 mm. It is
lighter in colour, more brassy in appearance, metallic and
green ; the eyes are sometimes a brilliant carmine.
188
XVII. ADDITIONAL LITERATURE.
Anderson, J. F. " The Differentiation of outbreaks of Typhoid
Fever due to infection by water, milk, flies and contacts."
Medical Record (Nov. 28, 1908), vol. 74, p. 909.
Bergey, D. H. " The Relation of Insects to the dissemination of
disease." New Yorh Med. Joum., vol. 85, p. 1120, 1907
Campbell, C. " House-flies and Disease." Brit. Med. Joum.,
1901 (2nd vol.), p. 980.
Chapman and Johnson. " House-flies and Disease." Ibid., p.
126.
Coplin, W. M. S. " The Propagation of Disease by means of
Insects, with special consideration of the common domestic
types." Pennsylvania Med. Joum., vol. 3, p. 241, 1900.
Cleaver, Emma 0. " The Role of Insects in the Transmission of
Disease: a Resume." Ibid., vol. 4, p. 457, 1900.
Dickenson, G. K. " The House-fly and its connection with dis-
ease dissemination." New York.
GiRAULT, A. A., and G. E. Sanders. " The Chalcidoid Parasites
of the Common House or Typhoid Fly (Musca domestica, L.)
and its allies." Psyche, vol. 16, pp. 119—131, 1909.
Howard, L. 0. " Further notes on the House-fly," in " Some
Miscellaneous Results of the work of the Division of Ento-
mology." U.S. Dept. of Agriculture, Division of Entomology,
Bull. No. 10 n.s., pp. 63—65, 1898.
Klein, E. " Flies as carriers of the Bacillus typhosus." Brit.
Med. Joum. (Oct. 17, 1908), p. 1150.
Manewaring, W. H. " Flies as carriers of Bacteria." Joum.
Applied Micr. (Rochester, N.Y.), vol. 6, p. 2402, 1903.
Martin, A. W. " Flies in relation to typhoid fever and summer
diarrhoea." Public Health (London), vol. 15, p. 652, 1903.
Morgan, H. de R. " Upon the Bacteriology of the Summer Diar-
rhoea of Infants." Brit. Med. Joum., April 21, 1906, 12 pp.,
and July 6, 1906, 11 pp.
189
ADDITIONAL LITERATURE
Morgan, H. de R., and J. C. G. Ledingham. " The Bacteriology
of Summer Diarrhoea. Proc. Roy. Soc. Med., Mar., 1909,
pp. 1 — 17 (separate pagination).
Nash, J. T. C. " The waste of infant life." Joum. Roy. Sa?iit.
Inst., vol. 26, pp. 494—498, 1905.
Nash, J. T. C. " Annual Report of the Medical Officer of Health,
Borough of Southend on Sea." 1906.
Nash, J. T. C. " Special Report on Epidemic Diarrhoea, Borough
of Southend on Sea." 16 pp., 1 chart, 1906.
Nash, J. T. C. " Second Report on same." 28 pp., 1906.
Nash, J. T. C. " The Prevention of Summer or Epidemic Diar-
rhoea." The Practitioner, May, 1906, 12 pp.
Nash, J. T. C. " House-flies as carriers of Disease." Joum. of
Hygiene, vol. 9, pp. 141—169, 1909.
Niven, J. " Annual Report on the Health of the City of Man-
chester." 1904.
Schilling, C. " Die Ubertragung von Krankheiten durch In-
sekten und ihre Bekampfung." Gesundh. Ingeniewr, vol.
30, pp. 300—303, 1907.
ERRATA.
P. 3, read Berlese for Belese.
P. 21, read macrochaetae for macrochaebae.
P. 154, read Ilaematopota for Haemalopota.
190
INDEX.
A
Abdomen, external structure, 20.
Abdominal ganglia, 25.
nerves, 25.
Acarina. See Mites.
Acorns muscarum, 129.
Accessory glands, female genital, 37.
Africa, 108.
Air sacs, 31, 32, 33, 34.
Alar membrane, 14.
muscles, 35.
Alimentary system of fly, 26-30.
of larva, 83-88.
Aldridge, 111, 149.
Allies and co-inhabitants of houses, 110.
America, 108.
Ampulke, 15.
Anopheles maculipemiis, 91
Antenme, 8.
Antliomyia radicum, 2, 109, 114, 115.
Anthrax, 153-155.
bacteriological evidence for trans-
mission of, 155, 156.
Arista, 8.
Arnold, 124, 152, 161.
Ascaris, 142.
Asia, 108. See also India.
Aspergillus mge.r, 179, 181.
Astoma paraxiticum, 129.
Atoma pnraxitin/m, 129.
Audonin, 14.
Austen, 2, 108, 148.
Australia, 108.
Axenfeld, 159.
B
Bacillus anvylobacter, 180.
B. antJiracis, 117, 119, 154, 155.
B. roli commune, 152, 153, 179, 181.
Bacillus, Koch- Weeks', 159, 160.
/,'. lactis acidi, 181.
It. prodigiosus, L61.
subtiUs, 179, 181.
/{. tumescens, 180, 181.
Bacteria. See Disease.
number carried, 151, 162, 103.
Balfour, 112, 159.
Banks, 129.
Beetles, predatory, 125.
Berg, 125.
Berlese, 3, 40, 65.
Bermuda, camp conditions in, 149.
Bibliography, 48-50, 98-100, 164-173.
Bigot, 112.
Blood of fly, 35.
of larva, 92.
Blowfly. See Calliplwra erytlirocephala
and O. vomitoria.
Blue-bottle. See C. eryihrocefliola.
Bodo muscce-domesticce, 133.
Body cavity, of fly, 35.
of larva, 90.
Bollinger, 154.
Bouche, 2, 57.
Brauer, 71.
Breeding habits, 57-60, 63, 171, 172, 183.
rapidity of, 64.
Brefeld, 131.
Buchanan (R. M.), 152, 154, 158, 161.
Buchanan (W. J.), 156.
C
Calandruccio, 141.
Callvphoraeryihrocephala, 3, 4, 109, 110.
Ill, 117-119, 132, 153, 164.
development of, 118.
C. vomitoria, 117, 154, 156. See also
C. erytlirocephala.
Camps, flies in military, 144, 145, 146,
147, 148, 149, 150, 183.
Carter, 139.
Celli, 151, 158, 161.
Cephalic ganglion, 23.
air sacs, 32.
Cephalothoracic nerve cord, 24.
Cephalopharyngeal skeleton of first
instiir, 67.
of second instar, 67.
of mature larva, 84.
muscles, 76.
Oerromonas m usc-ce-domesticce, 133.
( 'erebral lobes, larval, 80.
Ceylon, Boer camp in, 149.
Cherries nodosus, 125-128.
Cholera, 155-158.
bacteriological evidence, 156-158.
Chordonotal sense organs, 19.
191
INDEX
Church, 148.
Chrysops, 154.
Chyle stomach of fly, 27.
of larva, 86.
Cladosjjoriiivi Jierbarum, 179-180.
( llavicle, 13.
Clypeus, 7, 8.
Co-inhabitants of houses, 110.
( 'omnia bacillus, 156.
Comstock and Needham, 17.
Conjunctivitis. See Ophthalmia.
Copulation, 65.
Copulatory vesicles, 37, 65.
Costa, 16.
Crithidia muscce-domestica, 138, 139.
Crop, 26.
Cyclorrapha, 4.
Cyprus, 109
Gyrtbnevra stabulans. See Muscina
stabulans.
D
Davaine, 154.
Dell, 91.
Dermestid beetle, 125.
Destruction of larvae.
Development, 64-70.
rate of, 62.
factors governing, 60.
Diarrhoea, 153, 164, 174.
infantile or summer, 154, 174-178.
Diesing, 140.
Dinychella asperata, 130.
Discal sclerites of proboscis, 11.
retractor muscles of, 43.
Disease, dissemination of organisms of,
142-164, 174-184.
factors affecting dissemination of,
143, 176.
Distance flown. See Flight.
Distribution of M. domestica, 108.
Donovan, 128.
Dorsales muscles, 21.
Dorsal vessel of fly. See Heart.
■ of larva, 90.
Dorso-pleural membrane, 14.
Drone-fly. See Eristalis.
Dunne, 147.
Dutton, 183.
Dwyer, 112.
Dysentery, 149.
E
Egg, 66.
Egypt, ophthalmia in, 158-160.
Ejaculatory duct, 38.
sac, 38.
apodeme, 38.
Empusa muscm, 122, 130-133.
Enemies, 125.
Entomophthoreae, 130.
Entomophthora calliphora, 132.
Entopleura, 15.
Entothorax, 16.
Epicephalon, 8.
Epicranium, 7, 8.
Epiopticon, 23.
Epistomium, 8.
Eston and Mason, 163.
Europe, 108.
Eurotium, 181.
Exclusion of imago, 70.
External structure of fly, 6.
of larva, 70.
Eyes, 7, 24.
F
Fabricius, 4.
Face, 8.
Facialia, 7.
Fat-body of fly, 35.
of larva, 91.
Fermentation, effect of, 57, 62.
Filaria muscw, 139, 140.
F. stomoxeos, 139.
Filth trenches and flies, 59, 60, 112, 144-
148. See also Breeding habits.
Finmark, 108.
Firth and Horrocks, 151.
Flagellate parasites, 133-139.
Flight, 123, 124.
Fly mite, brown, 129.
Food of larva. See Breeding habits.
effect of character of,61.
influence of, 121.
Frontal sac, 70. See also Ptilinium.
lobes, 23.
Fronto-orbital bristles, 8.
Fulcrum, 12.
retractor muscles of, 42.
Fungal disease. See Empusa.
spores, carriage of, 178-182.
Fungiform bodies, 23.
Furca, 9.
retractor muscles of, 43.
Fusarum roseum, 180, 181.
G
Gamasids, 128, 130.
Ganglion of larva, 79.
Geer, de, 2, 57.
Genae, 7.
Generali, 140.
Geoffroy, 129.
Gerris fossarum, 139.
Giard, 132.
Girault and Saunders, 186.
INDEX
192
Glossitia, 26.
Godfrey, 126.
Gonapophyses, male, 39, 65.
female, 37, 65.
Gonococci, 159.
Grassi, 141.
Griffith, 56, 60, 63, 64.
Gula, 7.
Gulo-mental plate, 7.
Gustatory papillae, 12, 44.
bristles, 44.
Giissow, 178.
H
IJribronema muscce, 139-141.
Hcematobia stimulans, 153.
Halteres, 19.
Hamer, 110, 115.
Hamilton, 152.
Hammond, 21, 22.
Harman, 160.
Haustellum, 9, 10.
retractor muscles, 42.
flexor muscles, 42.
extensor muscles, 43.
Hayward, 158.
Head capsule, 6.
internal structure of, 41.
Heart of fly, 35.
of larva, 90, 91.
Henneguy, 71.
Hepworth, 3.
H erpetomonas donvani 138.
//. jaculum,, 134.
H. lygati, 134.
//. muscce-domesticce, 133-138.
Hibernation, 122, 123.
Hickson, 23, 24, 128.
Hoffmann, 158.
Holmgren, 85.
1 1 omalomyia canicularis, 2, 109, 110, 111,
113, 114, 143, 153, 164.
//. Sedans, 114, 164.
Howard, 5, 58, 110, 116, 118, 119, 120,
148, 163.
Humeri, 14.
Humidity, effect on development, 61
Hypopharynx, 10.
Hypopharyngeal tube, 10.
Hypotremata, 13, 14.
I
[maginal discs, 92.
cephalic, 93.
thoracic, 94.
Imms, 91.
India, camp conditions in, 149.
integument, larval, 87.
interclavicle, 13.
Intestine of Hy, proximal, 27.
distal, 28.
larval, 87.
Intestinal myiasis, 163, 164.
J
Jackson, 150, 151.
Jowl, 7.
Jugum, 7.
Jugulares, 13.
K
Kammerer, 124.
Koch-Weeks' bacillus, 159, 160.
Keller, 3, 57.
Kent, 134.
Kerr, 163.
Kerosene, effect of, 185.
Kew, 126.
Kirby and Spence, 128.
Koch, 159.
Kraepelin, 9, 12, 45.
Kunckel d'Herculais, 21, 92.
L
Labial nerves, 24.
Labium, 9, 10.
Labium-hypopharynx, 10.
dilator muscles of, 44
Labium epipharynx, 10.
Lapland, 108.
Larva, first instar, 66, 67.
Second instar, 67, 68.
third instar or mature larva, 68,
70-98.
external features, 70.
Latrines. See Filth trenches.
Laveran, 158.
Leger, 134, 137.
Legs, 20.
Leishmann-Donovan body, 138.
Light, effect of, 82, 122.
Lime, effect of chloride of.
Lingual glands, 28.
Lingard and Jennings, 134, 138, 139.
Linstow, von, 139.
Locomotory pads of larva, 72.
Locomotion of larva, 78.
Longitudinal and tracheal trunks of
larva, 89.
Lowne, 3(i, !), '21, 24, 29, 71, 73, 88, 92.
Lucilia ccesar, 120, 154.
Lunule, 8, 41.
Lyperosia irritans, 153.
M
MacCalliin, If,!).
Macloskie, 3.
Macrae, '157.
193
INDEX
Macrosporium, 180.
Maddox, 156.
Malpighian tubes of fly, 29.
■ of larva, 87.
Malta, 155.
Mantis, 126.
Maxillae, 9.
Measures, preventive, 185.
Melanostomum scalare, 131.
Melophagus uriiu/i<, 78.
Merlin, 3.
Mesenteron of fly, 27.
■ of larva, 86.
Mesophragma, 16.
Mesothorax, 14, 15.
Metafurca, 16.
Metathorax, 16.
Methods, 5, 56.
Micrococcus pyogenes aureus, 180, 181.
.1/. urece, 179, 181.
Michael, 129.
Middens. 60, 114, 150.
Milk, infection of, 157, 162, 163.
Minchin, 26.
Mites borne by house-flies, 128, 130. '
Moniez, 127.
Morgan, 175.
— and Ledingham, 175.
Morgan's bacillus. 175.
Mortality, infantile. 174-178.
Muses. 1 I.").
Mucor racemosa, 181.
Murray, 129.
Musca corvina, 113, 164.
M. domestica sub. sp. determinata, 111.
M. enteniata, 112.
Muscina stabulans, 109, 110, 119, 120.
Muscles of body wall of larva, 73.
Myiasis, 163, 164.
N
Nash, 174.
Nasonia brevicornis, 187.
Nematode. 139-141.
Nepa rinerca, 138.
Nervous system of fly, 22, 26.
of larva, 79-83."
Nervures of wings, 17, 18, 19, 172.
Neuroblast, 79.
Newport, 71.
Newport's segment, 72.
Ncwstead, 56, 57, 114, 116.
New York harbour, 150, 151.
New Zealand, 108.
Nicholas, 155.
Niven, 152, 177.
Nuttall, 142, 153, 155, 160.
Numerical occurrence, 109, 110.
Nymph, 69.
0
Occellar triangle, 8.
nerve, 23.
Ocelli, 8, 23.
Occipital foramen, 7.
ring, 7.
Occurrence. See Distribution.
CEsophagus of fly, 26.
of larva, 85.
Oil, effect of
Olive, 134.
Ophthalmia, 158-160.
Opticon, 23.
Oral lobes of fly, 9, 11, 44.
of larva, 83.
pit, 11.
Ovaries, 36.
Ovipositor, 37.
Oxyuris, 141.
P
Packard, 3, 57, 125.
Para, 108.
Paracephala, 7.
Parapteron, 16.
Paraphyses, 10.
Parasites, true, 133, 141, 186.
occasional, 125.
hyinenopterous, 186.
Parasitic worms, 139.
dissemination of, 141, 142.
Patton, 134, 135, 136, 138.
P&nicillium glaucum, 179, 180, 181.
Penis, 40, 41, 65.
Pericardium of fly, 35.
of larva, 91.
Periopticon, 23.
Phaiacrocera, 85.
Pharyngeal nerve, 24.
Pharynx ol fly, 12, 26.
of larva, 84.
PJdebotamus, 121.
Physiology, 121-124.
Piana, 140.
Pickard-Cambridge, 126.
Piercing skin, inability of .1/. domestica,
142.
Plague, 160, 161.
Pollenia rudis, 111.
Portchinski, 118, 120.
Preventive measures, 185.
Proboscis, skeleton of, 9.
musculature of, 42.
extension of, 45.
Procerebrum, 23.
Prothorax, 13.
Prowazek, 134, 135, 136, 137, 139.
Proventriculus of Ily, 27.
of larva, 85.
INDEX
194
Pseudocephalon, 71.
Pseudoscorpionidca, 25.
Psychoda punctata, 91.
Psychoda, 119, 121.
Pteronialid parasites, 186.
Ptilinium, 8, 41.
Pupa, 68, 69.
Pupal spiracles, 69.
Pustule, malignant, 154.
Pycnbsoina chloropyga, 148.
Q
Quill, 149.
R
Raimbert, 154.
Reaumur, 2, 65.
Reed, 145.
Regeneration of lost parts, 124.
Reconstruction method, 6.
Rectal glands, 28, 30.
valve, 28.
Rectum of fly, 28.
of larva, 87.
Reproductive system, 36-41.
organs of female, 36-38.
— — organs of male, 39-41.
Respiratory system of fly, 30- 34.
of larva, 88-90.
Riley, 118, 119, 129.
Rogers, 138.
Root-maggot. See Anthomyia radicum.
Rostrum, 9.
S
Saccliaromyces, 179, 181.
Salivary glands of fly, 28.
of larva, 87.
Salivary duct, lingual, 10.
Samuelson and Hicks, 3.
Sangree. 152.
Sarcina lutea, 17!). 180, 181.
S. ventriculi, 180, 181.
Sawtchenko 156.
Scape, 8.
Schiner, 4, 71.
Sciara, 133.
Scutum, 14.
Scutellum, L5.
Segmental muscles, 22.
Sella, 13.
Sellars, 152.
Sensory tubercles of larva, 72, 82.
organs of larva, 82.
Sex distinction, 8.
Shipley, 141.
Simmonds, 157.
Small house-liy. See llomaloinyia
canicularis.
Smith, 60, 113, 148, 149.
Spermathecae, 36.
Spillmann and Haushalter, 157.
Spiracle, anterior thoracic, of fly, 14, 30.
posterior thoracic, of fly, 33.
abdominal, 34.
Spiracular processes of larva, anterior,
88.
Spiracles of larva, posterior, 89.
Staphylococcus pyogenes omens, 161.
Stable fly. See Stomoxy* calcitrant.
Stein, 133.
Stephens, 164.
Sternberg, 145, 146.
Sternodorsales muscles, 21.
Stomato-gastric nervous system. See
Visceral nervous system.
Stomoxys calcitrcms, 2, 26, 63, 109, 110,
111, 115, 116, 117, 140, 153.
Storm fly. See S. calcitrans.
Summary of anatomy of fly, 45-48.
of larva, 95-98.
Summer diarrhoea. See Infantile
diarrhoea.
Supra-cesophageal ganglion, 22, 23.
Syphilis, 163.
Syrphid, Em pitta on, 131, 133.
T
Tabanidfe, 153.
7' 1 1 nia solium, 141.
7. nana, 142.
Taschenberg, 3, 58, 66, 120.
Taylor, 182.
Temperature, effect on development, 60.
effect on fly, 121, 122.
Testes, 38.
Thaxter, 131, 133.
Thalami, 23.
Thorax, 12, 20.
Thoracic muscles, 21, 22.
ganglion, 24, 25.
nerves, 25.
Tizzoni and Cattani, 156.
Tooth, 147, 148.
Tracheal sacs. 31, 32.
trunks of larva, 89.
Trichocephalns, Ml.
Tritocerebrum, 23.
Trombidium parasiticum, 129.
Trox suberosus, 125.
Tuberculosis, 157-158.
Tulloch, 26.
195
INDEX
Typhoid fever, 144-153, 182.
epidemiological evidence, 144-151,
182.
■ bacteriological evidence, 151-153.
Commission of U.S., 144, 146.
U
Uffelman, 157.
V
Vagina, 36, 65.
Vaney, 91.
Vascular system of fly, 35.
■ of larva, 90-92.
Vas deferens, 38.
Vaughan, 144.
Veeder, 146.
Ventriculus of fly, 27.
of larva, 86.
Vertex, 8.
Vesicula; seminales, 36.
Vcspa germanica, 125.
Vignon, 87.
Visceral nervous system of larva, 82.
Volucdlu, 21, 22.
W
Walker, 111.
War, Spanish-American, 144, 145, 146.
South African, 144, 147, 148.
Wasp, 125.
Weir, 149.
Weismann, 71, 92.
Werner, 138.
Wesche, 3.
Wings, 17, 172.
Wing base, 16.
Winter, 132.
Winter, breeding in, 63, 171, 172.
habits. See Hibernation.
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