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STUDIES IN COMPARATIVE ANATOMY-III

THE STRUCTURE AND LIFE-HISTORY

THE COCKROACH

(PERIPLANETA ORIENTALIS)

Jhitrotnution tcr the Stubn of Jirj

L. C. MIALL

PROFESSOR OF BIOLOGY IX THE YORKSHIRE COLLEGE, LEEDS

AND

ALFPvED DENNY

LECTURER OX BIOLOGY IX THE FIRTH COLLEGE, SHEFFIELD

LONDON: LOVELL REEVE & CO.
LEEDS: RICHARD JACKSON

1886

STUDIES IN COMPARATIVE ANATOMY.

I.- -THE SKULL OF THE CROCODILE. A Manual for
Students. By Professor L. C. MIALL. Svo, 2,s. 6d.

II.— THE ANATOMY OF THE INDIAN ELEPHANT. By

Professor L. C. MIALL and F. GREENWOOD. Svo, 5s.

III.— THE COCKROACH : An Introduction to the Study of
Insects. By Professor L. C. MIALL and A. DENNY. Svo, 7*. Gd-

IV.— MEGALICHTHYS ; A Ganoid Fisli of the Coal Measures.
By Professor L. C. MIALL (In preparation).

MAY BE HAD OF

LOVELL REEVE & CO., LONDON;
RICHARD JACKSON, LEEDS.

PBEFACE.

THAT the thorough study of concrete animal types is a
necessary preliminary to good work in Zoology or Comparative
Anatomy will now be granted by all competent judges. At a
time when these subjects, though much lectured upon, were
rarely taught, Dollinger, of Wiirzburg, found out the right
way. He took young students, often singly, and made them
master such animal types as came to hand, thereby teaching
them how to work for themselves, and fixing in their minds a
nucleus of real knowledge, around which more might crystallise.
" What do you want lectures for ? Bring any animal and
dissect it here," said he to Baer, then a young doctor longing
to work at Comparative Anatomy.* It was Dollinger who
trained Purkinje, Pander, Baer, and Agassiz, and such fame
cannot be heightened by words of praise. In our own time and
country Bellinger's methods have been practised by Professor
Huxley, whose descriptive guides, such as the Elementary
Biology and the delightful little book on the Crayfish, now
make it easy for every teacher to work on the same lines.
From the description of the Cockroach in Huxley's Anatomy
of Invertebrated Animals came the impulse which has
encouraged us to treat that type at length. It may easily
turn out that in adding some facts and a great many words to
his account, we have diluted what was valuable for its
concentration. But there are students — those, namely, who
intend to give serious attention to Entomology — who will find
our explanations deficient rather than excessive in detail. It
is our belief and hope that naturalists will some day recoil from
their extravagant love of words and names, and turn to

* Baer's account of Dollinger is to be found in the Leben und Schriften von K. E.
von Baer, § 8.

PREFACE.

structure, development, life-history, and other aspects of the
animal world which have points of contact with the life of
man. We have written for such as desire to study Insects on
this side.

Whoever attempts to tell all that is important about a very
common animal will feel his dependence upon other workers.
Much of what is here printed has been told before. The large
number of new figures is, however, some proof that we have
worked for ourselves.

It is a pleasant duty to offer our thanks for friendly help
received. Professor Felix Plateau, of Ghent ; Mr. Joseph
Nusbaum, of Warsaw ; and Mr. S. H. Scudder, of Cambridge,
Massachusetts, have very kindly consented to treat here of
those parts of the subject which they have specially illustrated
by their own labours.* Mr. E. T. Newton, of the Jermyn
Street Museum, has lent us the wood blocks used to illustrate
one of his papers on the Brain of the Cockroach. A number
of the figures have been very carefully and faithfully drawn
for us by Miss Beatrice Boyle, a student in the Yorkshire
College. We are much indebted to Dr. Murie, the Librarian
of the Linnean Society, for procuring us access to the
extensive literature of Insect Anatomy, and for answering
not a few troublesome, .questions.

Five articles on the Cockroach were contributed by us
to Science Gossip in 1884, and some of the figures were then
engraved and published.

In issuing a book which has been long in hand, but which
can never hope to be complete, we venture to adopt the
words already used by Leydig concerning his Lehrbuch der
Histologie : — " Die eigentlich nie fertig wird, die man aber
fur fertig erklaren muss, wenn man nach Zeit und Umstiinden
das Mo^lichste orethan hat."

o o

* Prof. Plateau's chief communications will be found on pp. 131 and 159 ;
Mr. Nusbaum has furnished the account of the Development of the Cockroach,
pp. 180 to 195 ; and Mr. Scudder the Geological History of the Cockroach, chap. xitj

CONTENTS.

CHAP. PAGE

I. — WRITINGS ON INSECT ANATOMY ... ... ... 1

II. — THE ZOOLOGICAL POSITION OF THE COCKROACH ... 9

III. — THE NATURAL HISTORY OF THE COCKROACH... ... 17

IV. — THE OUTER SKELETON ... ... ... ... ... 28

V. — THE MUSCLES; THE FAT-BODY AND CCELOM ... ... 71

VI. — THE NERVOUS SYSTEM AND SENSE ORGANS ... ... 86

VII. — THE ALIMENTARY CANAL AND ITS APPENDAGES ... 113

VIII. — THE ORGANS OF CIRCULATION AND RESPIRATION (in-
cluding a section on the Respiratory Movements of
Insects, by Prof. Felix Plateau, of Ghent) ..." ... 133

IX. — REPRODUCTION ... ... ... ... ... ... 167

X. — DEVELOPMENT (including a section on the Embryonic
Development of the Cockroach, by Joseph Nusbaum,
of Warsaw) ... ... ... ... ... ...181

XI. — THE COCKROACH OF THE PAST, by S. H. Scudder, of

the U.S. Geological Survey ... ... ... ... 205

APPENDIX :-

PARASITES OF THE COCKROACH.
SENSE OF SMELL IN INSECTS.

%* Where the species is not named, it is to be understood that the figures

are drawn from the Cockroach.

39349

LEEDS :

McCORQUODALE & CO. LIMITED,
BASINGHALL STREET.

STUDIES IN COMPAEATIVE ANATOMY.— No. III.

THE COCKROACH.

CHAPTER I.

WRITINGS ON INSECT ANATOMY.

MARCELLO MALPIGHI. 1628-1694.
JAN SWAMMERDAM. 1637-1680.
PIERRE LYONNET. 1707-1789.
HERCULE STRAUS-DURCKHEIM. 1790-1865.

THE lovers of minute anatomy have always been specially
attracted to Insects ; and it is not hard to tell why. No other
animals, perhaps, exhibit so complex an organisation condensed
into so small a body. We possess, according^, a remarkable
succession of memoirs on the structure of single Insects, begin-
ning with the revival of Anatomy in the 17th century and
extending to our own times. The most memorable of these

Insect-monographs bear the names of Malpighi, Swanimerdam,
Lvonnet, and Straus-Diirckheim.

«,

Malpighi on the Silkworm.

Malpighi's treatise on the Silkworm (1669) is an almost
faultless essay in a new field. No Insect — hardly, indeed, any
animal — had then been carefully described, and all the methods

of work had to be discovered. " This research," says Malpighi,
" was extremely laborious and tedious ' (it occupied about a
year) " on account of its novelty, as well as the minuteness,
fragility, and intricacy of the parts, which required a special
manipulation ; so that when I had toiled for many months at
this incessant and fatiguing task, I was plagued next autumn
with fevers and inflammation of the eyes. Nevertheless, such

2 THE COCKROACH.

was my delight in the work, so many unsuspected wonders of
nature revealing themselves to me, that I cannot tell it in
words." We must recall the complete ignorance of Insect-
anatomy which then prevailed, and remember that now for the
first time the dorsal vessel, the tracheal system, the tubular
appendages of the stomach, the reproductive organs, and the
structural changes which accompany transformation were
observed, to give any adequate credit to the writer of this
masterly study. Treading a new path, he walks steadily for-
ward, trusting to his own sure eyes and cautious judgment. The
descriptions are brief and simple, the figures clear, but not rich
in detail. There would now be much to add to Malpighi's
account, but hardly an}''thing to correct. The only positive
mistakes which meet the eye relate to the number of spiracles
and nervous ganglia — mistakes promptly corrected by Swarn-
merdam. Had the tract De Bombycibus been the one work of its
author, this would have kept his memory bright, but it hardly
adds to the fame of the anatomist who discovered the cellular
structure of the lung, the glandular structure of the liver and
kidney, and the sensory papillae of the skin, who first saw the
blood-corpuscles stream along a vessel, who studied very early
and very completely the minute structure of plants and the
development of the chick, and whose name is rightfully
associated with the mucous layer of the epidermis, the vascular
tufts of the kidney, and the follicles of the spleen, as well as
with the urinary tubules of Insects.

All that we know of Malpighi commands our respect. Pre-
cise and rapid in his work, keen to discover points of real
interest, never losing himself in details, but knowing when he
had done enough, he stands pre-eminent in the crowd of minute
anatomists, who are generally faithful in a few things, but very
unfit to be made rulers over many things. The last distinct
glimpse which we get of him is interesting. Dr. Tancred
Robinson, writing to John Ray, from Geneva, April 18th, 1684,
tells how he met Malpighi at Bologna. They talked of the
origin of fossils, and Malpighi could not contain himself about
Martin Lister's foolish hypothesis that fossils were sports of
nature. "Just as I left Bononia," he continues, "I had a
lamentable spectacle of Malpighi's house all in flames, occa-

WRITINGS OX INSECT ANATOMY. 6

sioned by the negligence of his old wife. All his pictures,
furniture, books, and manuscripts were burnt. I saw him in
the very heat of the calamity, and methought I never beheld so
much Christian patience and philosophy in any man before ; for
he comforted his wife, and condoled nothing but the loss of his
papers, which are more lamented than the Alexandrian Library,
or Bartholine's Bibliothece, at Copenhagen." *

Swammerdam on the Honey Bee.

Swammerdam's great posthumous work, the Biblia jSTaturse,
contains about a dozen life-histories of Insects worked out in
more or less detail. Of these the May-fly (published during
the author's life- time, in 1675) is the most famous ; that on the
Honey Bee the most elaborate. Swammerdam was ten years
younger than Malpighi, and knew Malpighi's treatise on the
Silkworm — a not inconsiderable advantage. His working-life
as a naturalist comes within the ten years between 1663 and

1673 ; and this short space of time was darkened by anxiety
about money, as well as by the religious fanaticism, which in
the end completely extinguished his activity. The vast amount
of highly-finished work which he accomplished in these ten
years justifies Boerhaave's rather rhetorical account of his
industry. Unfortunately, Boerhaave, whom we have to thank
not onlv for a useful sketch of Swammerdam's life, but also for

the preservation of most of his writings, was only twelve years
old when the great naturalist died, and his account cannot be
taken as personal testimony. Swammerdam, he tells us, worked
with a simple microscope and several powers. His great skill
lay in his dexterous use of scissors. Sometimes he employed
tools so fine as to require whetting under the microscope. He
was famous for inflated and injected preparations. As to his
patience, it is enough to say that he would spend whole days in
clearing a single caterpillar. Boerhaave gives us a picture of
Swammerdam at work which the reader does not soon forget.
" His labours were superhuman. Through the day he observed
incessantly, and at night he described and drew what he had
seen. By six o'clock in the morning in summer he began to

* Correspondence of John Ray, p. 142.

4 THE COCKROACH.

find enough light to enable him to trace the minutiae of natural
objects. He was hard at work till noon, in full sunlight, and
bareheaded, so as not to obstruct the light ; and his head
streamed with profuse sweat. His eyes, by reason of the blaze
of light and microscopic toil, became so weakened that he could
not observe minute objects in the afternoon, though the light
was not less bright than in the morning, for his eyes were
weary, and could no longer perceive readily."

Comparing Swammerdam's. account of the Bee with the use-
ful and amply illustrated memoir of Girdwoyn (Paris, 1876), it
is plain that two centuries have added little to our kuowledge
of the structure of this type. Much has been made out
since 1675 concerning the life-history of Bees, but of what was
to be discovered by lens and scalpel, Swammerdam left little
indeed to others. It is needless to dwell upon the omissions of
so early an explorer. Swammerdam proved by dissection that
the queen is the mother of the colony, that the drones are
males, and the working-bees neuters ; but he did not find out
that the neuters are only imperfect females. In this instance,
as in some others, Swammerdam's authority served, long after
his death, to delay acceptance of the truth. It is far from a
reproach to him that in the Honey Bee he lit upon an almost
inexhaustible subject. In the 17th century no one suspected
that the sexual economy of any animal could be so complicated
as that which has been demonstrated, step by step, in the
Honey Bee.

Lyonnei on the Goat Moth.

In L}7onnet's memoir on the larva of the Goat Moth (Traite
Anatomique de la Chenille qui ronge le bois de Saule, 1760*) we
must not look for the originality of Malpighi, nor for the wide
range of Swammerdam. One small thing is attempted, and
this is accomplished with unerring fidelity and skill. There is
something of display in the delineation of the four thousand and
forty-one muscles of the Caterpillar, and the author's skill as a
dissector is far beyond his knowledge of animals, wThether live
or dead. The dissections of the head are perhaps the most

* Copies dated 1762 have a plate representing the microscope and dissecting instru-
ments used by the author.

WRITINGS ON INSECT ANATOMY. 5

extraordinary feat, and will never be surpassed. Modern treatises
on Comparative Anatomy continue to reproduce some of these
figures, such as the general view of the viscera, the structure of
the leg, and the digestive tract. Nearly the whole interest of
the volume lies in the plates, for the text is little more than a
voluminous explanation of the figures.

It is not without surprise that we find that Lyonnet was an
amateur, who had received no regular training either in anatomy
or engraving, and that he had many pursuits besides the
delineation of natural objects. He was brought up for the
Protestant ministry, turned to the bar, and finally became

•/ ' ft/

cipher-secretary and confidential translator to the United Pro-
vinces of Holland. He is said to have been skilled in eight
languages. His first published work in Natural History con-
sisted of remarks and drawings contributed to Leaser's Insect
Theology (1742). About the same time, Trembley was prosecuting
at the Hague his studies on the freshwater Polyp, and Lyonnet
gave him some friendly help in the work. Those who care to
turn to the preface of Trembley Js famous treatise (Memoirea pour
servir a 1'histoire des Polypes d'eau douce, 1744) will see how
warralv Lyonnet's services are acknowledged. He made all

«/ •/

the drawings, and engraved eight of them himself, while
Trembley is careful to note that he was not only a skilful
draughtsman, but an acute and experienced observer. When
the \vork was begun, Lyonnet had never even seen the operation
of engraving a plate. TVandelaar, struck by the beauty of his
drawings, persuaded him to try what he could do with a burin.
His first essay was made upon the figure of a Dragon-fly, next
he engraved three Butterflies, and then, without longer appren-
ticeship, he proceeded to engrave the plates still required to
complete the memoir on Hydra.

Lyonnet tells us that the larva of the Groat Moth was not

quite his earliest attempt in Insect Anatomy. He began with
the Sheep Tick, but suspecting that the subject would not be
popular, he made a fresh choice for his first memoir. Enough
interest was excited by the Traite Anatomique to call for the
fulfilment of a promise made in the preface that the description
of the pupa and imago should follow. But though Lyonnet
continued for some time to fill his portfolio with drawings and

6 THE COCKROACH.

notes, he never published again. Failing eyesight was one
ground of his retirement from work. What he had been able
to finish, together with a considerable mass of miscellaneous
notes, illustrated by fifty- four plates from his own hand, wras
published, long after his death, in the Memoires du Museum
(XVIII.-XX.).

Straus-Diirckheim on the Cockchafer.

In beauty and exact fidelity Straus-Diirckheim's memoir on the

«/ i

Cockchafer (Considerations Generales sur 1' An atomic Comparee
des Animaux Articules, auxquelles on a joint P Anatomic Descrip-
tive du Melolontha vulgaris, 1828) rivals the work of Lyonnet.
Insect Anatomy was no longer a novel subject in 1828, but
Straus-DiArckheini was able to treat it in a new way. Writing
under the immediate influence of Cuvier, he sought to apply
that comparative method, which had proved so fertile in the
hands of the master, to the Articulate sub-kino-dom. This
conception wras realised as fully as the state of zoology at that
time allowed, and the Considerations Generales count as an
important step towards a complete comparative anatomy of
Arthropoda. Straus-Diirckheim had at command a great mass
of anatomical facts, much of which had been accumulated by his
own observations. He systematically compares Insects with
other Articulata, Coleoptera with other Insects, and the Cock-
chafer with other Coleoptera. Perhaps no one before him had
been perfectly clear as to the morphological equivalence of the
appendages in all parts of the body of Arthropods, and here he
was able to extend the teaching of Savigny. His limitations are

O O «.'

those of his time. If in certain sections we find his collection
of facts to be meagre, and his generalisations nugatory, we
must allow for the progress of the last sixty years — a progress
in which Straus-Diirckheim has his share. It is the work of
science continually to remake its syntheses, and no work
becomes antiquated sooner than morphological generalisation.

It is therefore no reproach to Straus-Diirckheim that his
treatise should now be chiefly valuable, not as " Considerations

»/

Generales," but as the anatomy of the Cockchafer. Long after
his theories and explanations have ceased to be instructive, when

WRITINGS ON INSECT ANATOMY. 7

the morphology and physiology of 1828 have become as obsolete
as the Ptolemaic astronomy, the naturalist will study these
exquisite delineations of Insect-structure with something of the
pleasure to be found in examining for the hundredth time a
delicate organism familiar to many generations of microscopic
observers.

The fidelity and love of anatomical detail which characterise
the description of the Cockchafer are not less conspicuous in
Straus-Diirckheim's Anatomic Descriptive du Chat (1846). Both
treatises have become classical.

We have seen how, in Straus-Durckheim's hands, Insect
anatomy became comparative. New studies — histology, embry-
onic development, and palaeontology — have since arisen to com-
plicate the task of the descriptive anatomist, and it appears to
be no longer possible for one man to complete the history
of any animal of elaborate structure and ancient pedigree.
As a method of research the monograph has had its day. The
path of biological discovery now follows an organ or a function
across all zoological boundaries, and it is in the humbler
office of biological teaching that the monograph finds its proper
use.

Later Insect Anatomists.

It is impossible even to glance at the many anatomists who
have illustrated the structure of Insects by studies, less simple
in plan, but not less profitable to science, than those of the
monographers. If we attempt to select two or three names for
express mention, it is with a conviction that others are left
whom the student is bound to hold in equal honour.

Dufour* laboured, not unsuccessfully, to construct a General
Anatomy of Insects, which should combine into one view a

crowxl of particular facts. The modern reader will gratefully
acknowledge his industry and the beauty of his drawings, but
will now and then complain that his sagacity does not do
justice to his diligence.

* Dufour. Eech. anat. et phys. sur les Hemipteres (1833) les Orthopteres, les
Hymenopteres et les Neuropteres (1841), et les Dipteres (1851). Mem. de 1'Institut,
Tom. IV., VII., XI. Also many memoirs in Ann. des Sci. Nat.

8 THE COCKROACH.

Newport,* a naturalist of greater weight and interest, is
memorable for his skill in minute dissection, for his many
curious observations upon the life-history of Insects (see, for
example, his memoir on the Oil-beetle), and especially for his
early appreciation of the value of embryological study.

Leydigf was the first to occupy fully the new field of Insect
histology, and point out its resources to the physiologist. In
all his works the student finds beauty and exactness of delinea-
tion, suggestiveness in explanation. Le^ydig's contributions to
Insect anatomy and physiology, valuable as they are to the
specialist, are not isolated researches, but form part of a new
comparative anatomy, based upon histology. Incomplete so
vast a work must necessarily remain, but it already extends
over considerable sections of the animal kingdom.

* Newport. Art. "Insecta," in Cycl. of Anat. and Phys. (1839), besides many
special memoirs in the Phil, and Linn. Trans.

f Leydig. Vom Bau des Thierischeu Korpers (1864), Tafeln zur vergl. Anatomic
(1864), Untersuchungen zur Anat. und Histologie der Thiere (1883), &c., besides
many special memoirs in Miiller's Archiv. , Zeits. f . wiss. Zool. , Nova Acta, &c.

CHAPTER II.

THE ZOOLOGICAL POSITION OF THE COCKROACH.

Sub-kingdom ARTHROPODA.

Class I. Crustacea.

,, II. Arachnida.

,, III. Myriopoda.

,, IV. INSECTA.

Order 1. Thysanura.

,, 2. Orthoptera.

,, 3. Neuroptera.

,, 4. Hemiptera.

,, 5. Coleoptera.

, , 6. Diptera.

,, 7. Lepidoptera.

,, 8. Hymenoptera.

THE place of the Cockroach in the Animal Kingdom is illus-
trated by the above table. It belongs to the sub-kingdom
Arthropoda, to the class Insecta, and to the order Orthoptera.

Characters of Arthropoda.

Arthropoda are in general readily distinguished from other
animals by their jointed body and limbs. In many Annelids
the body is ringed, and each segment bears a pair of appendages,
but these appendages are soft, and never articulated. The
integument of an Arthropod is stiffened by a deposit of the
tough, elastic substance known as Chitin, which resembles horn
in appearance, though very different in its chemical composition.
In marine Arthropoda, as well as in many Myriopoda and
Insects, additional firmness may be gained by the incorporation
of carbonate and phosphate of lime with the chitin. However
rigid the integument may be, it is rendered compatible with
energetic movements by its unequal thickening. Along defined,

THE COCKROACH :

usually transverse lines it remains thin, the chitinous layer,
though perfectly continuous, becoming extremely flexible, and
allowing a certain amount of deflection or retraction (fig. 1).

Fig. 1. — Diagram of Arthropod limb extended, retracted, and flexed.
Graber has given a similar figure (Insekten, fig. 8*).

The joints of the trunk and limbs may thus resemble stiff tubes.
Muscles are attached to their inner surface, and are therefore
enclosed by the system of levers upon which they act (fig. 2fi).
In Vertebrate animals, on the contrary, which possess a true
internal skeleton, the muscles clothe the levers (bones) to which

A B

Fig. 2. — Vertebrate and Arthropod joints. A, Vertebrate joint, the skeleton clothed
with muscles. B, Arthropod joint, the skeleton enclosing the muscles.

they are attached (fig. 2 A.). The whole outer surface of an
Arthropod, including the eyes, auditory membrane (if there is
one), and surface-hairs, is chitinised. Chitin may also stiffen

ITS ZOOLOGICAL POSITION. 11

the larger tendons, internal ridges and partitions, and the lining
membrane of extensive internal cavities, such as the alimentary
canal, and the air-tubes of Insects.

In most Arthropoda the body is provided with many appen-
dages. In Crustacea there are often twenty pairs, but some
Myriopoda have not far from two hundred pairs. Some of
these may be converted to very peculiar functions ; in particular,
several pairs adjacent to the mouth are usually appropriated to
mastication. One or more pairs of appendages are often trans-
formed into antennae.

The relative position of the chief organs of the body, viz. : —
heart, nerve-cord, and alimentary canal, is constant in Arthro-
poda. The heart is dorsal, the nerve-cord ventral, the
alimentary canal intermediate. (See fig. 3.) The oesophagus
passes between the connectives of the nerve-cord. Not a few
other animals, such as Annelids and Mollusca, exhibit the same
arrangement.

Arthropoda are not known to be ciliated in any part of the
body, or in any stage of growth. Another histological pecu-
liarity, not quite so universal, is the striation of the muscular
fibres throughout the bodv. In nianv Invertebrates there are

o •/ »/

no striated muscles at all, while in Vertebrates only voluntary
muscles, as a rule, are striated.

The circulatory organs of Arthropoda vary greatly in plan
and degree of complication, but there is never a completely
closed circulation.

The development of Arthropoda may be accompanied by
striking metamorphosis, e.g., in many marine Crustacea, but, as
in other animals, the terrestrial and fluviatile forms usually
develop directly. Even in Insects, which appear to contradict
this rule flatly, the exception is more apparent than real. The
Insect emerges from the egg as a fully formed larva, and so far
its development is direct. It is the full-grown larva, however,
which corresponds most nearly to the adult Myriopod, while the
pupa and imago are stages peculiar to the Insect. It is not by
any process of embryonic development, but by a secondary
metamorphosis of the adult that the Insect acquires the power
of flight necessary for the deposit of eggs in a new site.

THE COCKROACH

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ITS ZOOLOGICAL POSITION. 13

Characters of Insects.

Insects are distinguished from other Arthropoda by the
arrangement of the segments of the body into three plainly
marked regions — head, thorax, and abdomen ; by the three
pairs of ambulatory legs carried upon the thorax ; by the single
pair of antennae ; and by the tracheal respiration. Myriopods
and Arachnida have no distinct thorax. Most Crustacea have
two pairs of antennae, while in Arachnida antennoe are wanting
altogether. Crustacea, if they possess special respiratory organs
at all, have branchiae (gills) in place of tracheae (air-tubes). In
Arachnida, Myriopoda, and Crustacea there are usually more
than three pairs of ambulatorv leo:s in the adult.

JL *

The appendages of an Insect's head (antennae, mandibles,
maxillae) are appropriated to special senses, or to the operations
of feeding, and have lost that obvious correspondence with
walking legs which they still retain in some lower Arthropoda
(Peripatus, Limithis, Arachnida). The thorax consists of three*
segments, each of which carries a pair of ambulatory legs. No
abdominal legs are found in any . adult insect. The middle
thoracic segment may carry a pair of wings or wing-covers, and
the third segment a pair of wings.

The lower or less-specialised Insects, such as the Cockroach,
have nearly as many nerve-ganglia as segments, and the longi-
tudinal connectives of the nerve-cord are double. In the adult
of certain higher Insectsf (e.g., many Coleoptera, and some
Diptera) the nerve-ganglia are concentrated, reduced in number,
and restricted to the head and thorax ; while all the con-
nectives, except those of the oesophageal ring, may be outwardly
single.

The heart, or dorsal vessel, is subdivided by constrictions
into a series of chambers, from \vhich an aorta passes forwards
to the head.

Air is usually taken into the body by stigmata or breathing-
pores,^: which lie along the sides of the thorax and abdomen.

* In some Insects there are traces of a fourth thoracic segment,
f So also in some larvze (Calandra, (Estrus, &c.).

£ In some aquatic Insects the exchange of gases is effected by "pseudobranchire,"
and the tracheal system is closed.

14 THE COCKROACH :

It circulates through repeatedly-branching tracheal tubes, whose
lining is strengthened by a spiral coil. Air-sacs (dilated por-
tions of the air- tubes) occur in Insects of powerful flight.

The generative organs are placed near the hinder end of the
body.* Most Insects are oviparous, f The sexes are always dis-
tinct; but imperfect females (" neuters") occur in some kinds
of social Insects. Agamogenesis (reproduction by unfertilised
eggs) is not uncommon.

Orders of Insects.

The orders of Insects are usually denned with reference to
the degree of metamorphosis and the structure of the parts of
the mouth. Five of the orders (3, 5-8) in the table on page 9
undergo complete metamorphosis, and during the time of most
rapid change the insect is motionless. In the remaining orders
(1, 2, 4) there is either no metamorphosis (Thysanura), or it is
incomplete — i.e., the insect is active in all stages of growth.
Among these three orders we readily distinguish the minute and
wingless Thysanura. Two orders remain, in which the adult is
commonly provided with wings ; of these, the Orthoptera have
biting jaws, the Hemiptera, jaws adapted for piercing and
sucking.

The name of Black Beetle, often given to the Cockroach, is
therefore technically wrong. True Beetles have a resting or
chrysalis stage, and may further be recognised in the adult state
by the dense wing-covers, meeting along a straight line down
the middle of the back, and by the transversely folded wings.
Cockroaches have no resting stage, the wing-covers overlap, and
the wings fold up fan-wise.

Further Definition of Cockroaches.

In the large order of Orthoptera, which includes Earwigs,
Praying Insects, Walking Sticks, Grasshoppers, Locusts,
Crickets, White Ants, Day-flies, and Dragon-flies, the family of
Cockroaches is defined as follows : —

* Dragon-flies have the male copulatory apparatus, but not the genital aperture,
in the fore part of the abdomen.

f Aphis and Cecidomyia are at times viviparous, and a viviparous Moth has been
observed by Fritz Miiller (Trans. Entom. Soc. Lond., 1883).

ITS ZOOLOGICAL POSITION.

. Family Blattina. Body usually depressed, oval. Pronotum
shield-like. Legs adapted for running only. Wing-
covers usually leathery, opaque, overlapping (if well
developed) when at rest, anal area defined by a furrow
(fig. 4). Head declivent, or sloped backwards, retractile
beneath the pronotum. Eyes large, ocelli rudimentary,

usually two. antennae long and slender.

*/ ^-j

intcrno-median area

I'F.IKS

Fig- 4. — Generalised sketch of Cockroach wing-cover.

About eight hundred species of Cockroaches have been
defined, and to facilitate their arrangement, three groups have
been proposed, under which the different genera are ranked.*

Group 1. Both sexes wingless (Polyzosteria).

Group 2. Males winged, females wingless (Perisphceria,

Heteroyamia).

Group 3. Both sexes with more or less developed wings
(about 7 genera).

* For descriptions of the species Fischer's Orthoptera Europsea (1853) or Brunner
von*>Wattenwyl's Nouveau Systetne des Blattaires (1865) may be consulted. The
classification adopted by the last-named author is here summarised.

BLATTARI.E.
A. — Femora spinous (Spinosce).

Fam. 1. — Ectobidce. Seventh abdominal sternum undivided in female. Sub-
anal styles absent in male. Wings with triangular apical area. Ectobia,
including E. lapponica (Blatta) and other genera.

Fam. 2. — Phyttodromidce. Seventh abdominal sternum undivided in female.
Sub-anal styles usual in male (0 or rudimentary in Phyllodromia). Wings
without triangular apical area. Phyllodromia, including P. germanica (Blatta)
and other genera.

Fam. 3. — Epilampridce.

Fam. 4. — Periplanetidce. Seventh abdominal sternum divided in female.
Sub-anal styles conspicuous in male. Polyzosteriat Periplaneta, &c.

B. — Femora not spinous (Muticce)-

Families.— Chorisoneuridce, Pancliloridce, Perisphceridce, Corydldce, Hetero-

gamidce, Blaberidce, Panesthidce.

Many useful references will be found in Scudder's Catalogue of N. American
Orthoptera, Smiths. Misc. Coll., viii. (1868).

16 THE COCKROACH.

In Group 3 occur the only two genera which we shall find it
necessary to describe — viz., Blatta, which includes the European
Cockroaches, and Periplaneta, to which belong the Cockroaches
of tropical Asia and America.

Genus Blatta. A pulvillus between the claws of the feet.
The seventh sternum of the abdomen entire in both
sexes ; sub-anal styles rudimentary in the male.

Genus Periplaneta. Readily distinguished from Blatta by
the divided seventh abdominal sternum of the female,
and the sub-anal styles of the male.

Two species of Periplaneta have been introduced into Europe.
These are —

1. P. orientalis (Common Cockroach, Black Beetle). Wing-
covers and wings not reaching the end of the abdomen
in the male ; rudimentary in the female.

2. P. americana (American Cockroach). Wing-covers and
wings longer than the body in both sexes.

CHAPTER III.

THE NATURAL HISTORY OF THE COCKROACH.

SPECIAL REFERENCES.

HUMMEL. Essais Entomologiques, No. 1 (1821).
CORNELIUS. Beitrage zur niihern Kenntniss von Periplaneta orientalis (1853.)

GIRARD. La domestication des Blattes. Bull. Soc. d' Acclimatisation, 3e Ser.,
Tom. IV., p. 296 (1877).

Range.

THE common Cockroach is native to tropical Asia,* and long
ago made its way by the old trade-routes to the Mediterranean
countries. At the end of the sixteenth century it appears to
have got access to England and Holland, and has gradually
spread thence to every part of the world.

Perhaps the first mention of this insect in zoological literature
occurs in Moufet's Insectorum Theatrum (1634), where he
speaks of the Blattse as occurring in wine cellars, flour mills, &c.,
in England. It is hard to determine in all cases of what insects
he is speaking, since one of his rude woodcuts of a " Blatta" is
plainly Blaps mortisaga ; another is, however, recognisable as
the female of P. orientalis; a third, more doubtfully, as the male
of the same species. He tells how Sir Francis Drake took the
ship " Philip," f laden with spices, and found a great multitude
of winged Blattoo on board, " which were a little larger, softer,
and darker than ours." Perhaps these belonged to the American
species, but the description is obscure. Swammerdam also was
acquainted with our Cockroach as an inhabitant of Holland
early in the seventeenth century. He speaks of it as "insectum

* Linnaeus was certainly mistaken in his remark (Syst. Nat., 12th ed.) that this
species is native to America, and introduced to the East — "Habitat in America:
hospitatur in Oriente. " He adds, " Hodie in Russia? ad jacentibus regionibus frequens ;
incepit nuperis temporibus Holmite, 1739, uti dudum in Finlandia."

1" This must have been the "San Felipe," a Spanish East Indiaman, taken in 1587.
See Motley, United Netherlands, Vol. II., p. 283.

18 THE COCKROACH:

illud Indicum, sub nomine Kakkerlak satis notum," and very
properly distinguishes from it " the species of Scarabaeus '
(Blaps), which Moufet had taken for a Blatta.*

The American Cockroach is native to tropical America, but
has now become widely spread by commerce. An Australian
species also (P. auztralasice) has begun to extend its native
limits, having been observed in Sweden, f Belgium, Madeira,
the East and West Indies,:}: Florida,§ &c. In Florida it is said
to be the torment of housekeepers.

To the genus Blatta belong a number of small European
species, which mostly lurk in woods and thickets. Some of
these are found in the south of England. B. lapponica is one of
the commonest and most widely distributed. It is smaller than
the common Cockroach, and both sexes have long wings and
wing-cases. The males are black and the females yellow. It is
found on the mountains of Norway and Switzerland as high as
shrubs extend, and when sheltered by human dwellings, can
endure the extreme cold of the most northern parts of Europe.
This is the insect of which Linnaeus tells, that in company with
Silpha lapponica it has been known to devour in one day the
whole stock of dried but unsalted fish of a Lapland village.
B. germanica also has the wings and wing-cases well developed
in both sexes. Two longitudinal stripes on the pronotum, or
first dorsal plate of the thorax, are the readiest mark of this
species, which is smaller and lighter in colour than the common
Cockroach. It is plentiful in most German towns, and has been
introduced from Germany into many other countries ;|| but it
appears to be native, not to Germany alone, but to Asia and all
parts of central and southern Europe. Where and how it first
became domesticated we do not know.

* Biblia Natune, Vol. I., p. 216.

^ De Borck. Skandinaviens ratvingade Insekters Nat. Hist., L, i., 35.

+ Brunner. N. Syst. d. Blattaires, p. 234.

§ Scudder. Proc. Boston Soc. N.H., Vol. XIX., p. 94.

|| For example, the Russians often call it Proussaki, the Prussian Cockroach, and
believe that their troops brought it home with them after the Seven Years' War.
The native Russian name is Tarakan. In Finland and Sweden the same species is
called Torraka, which appears to be a corruption of the Russian word, and confirms
the account of Linnaeus quoted above.

B. germanica is found in the United States from the Atlantic to the Pacific. It is
generally known as the Croton Bug, because in New York it is often met with about
the water pipes, which are supplied from the Croton River (Dr. Scudder).

ITS NATURAL HISTORY. 19

The other species of Cockroaches which have been met with
in Europe are Pane/flora maderce, said by Stephens to be occa-
sionally seen in London, and Blabera gigantea, the Drummer of
the TVest Indies, which has often been found alive in ships in
the London Docks.

Blatta germanica, Periplaneta orientalis, and P. americana, are
so similar in habits and mode of life as to be interchangeable,
and each is known to maintain itself in particular houses or
towns within the territory of another species, though usually
without spreading.

Orientalis is, for example, the common Cockroach of England,
but germanica frequently gets a settlement and remains long in
the same quarters. H. C. R., in Science-Gossip for 1868, p. 15,
speaks of it as swarming in an hotel near Covent Garden, where
it can be traced back as far as 1857. In Leeds, one baker's
shop is infested by this species ; it is believed to have been
brought by soldiers to the barracks, after the Crimean war, and
to have been carried to the baker's in bread-baskets. We have
met with no instance in which it has continued to gain ground
at the expense of orientalis. Americana also seems well estab-
lished in particular houses or districts in England. H. C. R.
(loc. cit.) mentions warehouses near the Thames, Red Lion and
Bloomsbury Squares, and the Zoological Gardens, Regent's
Park. It frequents one single warehouse in Bradford, and is
similarly local in other towns with foreign trade.

Many cases are recorded in which germanica has been replaced
by flricntaUs, as in parts of Russia and Western Germany, but
detailed and authenticated accounts are still desired. On the
whole or ten falls seems to be dominant over both germanica and
americana.

The slow spread of the Cockroaches in Europe is noteworthy,
not as exceptional among invading species, but as one more
illustration of the length of time requisite for changes of the
equilibrium of nature. It took two centuries from the first
introduction of orientalis into England for it to spread far from
London. Gilbert White, writing, as it would appear, at some
date before 1790, speaks of the appearance of " an unusual
insect," which proved to be the Cockroach, at Selborne, and
says : " How long they have abounded in England I cannot say;

20 THE COCKROACH :

but have never observed them in my house till lately."* It is
probable that many English villages are still clear of the pest.
The House Cricket, which the Cockroaches seem destined to
supplant, still dwells in our houses, often side by side with its
rival, sharing the same warm crannies, and the same food. The
other imported species, though there is reason to suppose that
they cannot permanently withstand orientals, are by no means
beaten out of the field ; they retreat slowly where they retreat
at all, and display inferiority chiefly in this, that in countries
where both are found, they do not spread, while their competitor
does. It may yet require some centuries to settle the petty wars
of the Cockroaches.

It is also worth notice that in this, as in most other cases, the
causes of such dominance over the rest as one species enjoys are
very hard to discover. We cannot explain what peculiarities
enable Cockroaches to invade ground thoroughly occupied by
the House Cricket, an insect of quite similar mode of life :
and it is equally hard to account for the superiority of orientalis
over the other species. It is neither the largest nor the smallest;
it is not perceptibly more prolific, or more voracious, or fonder
of warmth, or swifter than its rivals, nor is it easy to see how
the one conspicuous structural difference — viz., the rudimentary
state of the wings of the female, can greatly favour orientalis.
Some slight advantage seems to lie in characteristics too subtle
for our detection or comprehension.

Food and Habits.

As to the food of Cockroaches, we can hardly except any
animal or vegetable substance from the long list of their depre-
dations. Bark, leaves, the pith of living cycads, paper, woollen
clothes, sugar, cheese, bread, blacking, oil, lemons, ink, flesh,
fish, leather, the dead bodies of other Cockroaches, their own
cast skins and empty egg-capsules, all are greedily consumed.
Cucumber, too, they will eat, though it disagrees with them
horribly.

In the matter of temperature they are less easy to please.
They are extremely fond of warmth, lurking in nooks near the

* Bell's Edition, Vol. I., p. 454.

ITS NATURAL HISTORY. 21

oven, and abounding in bakehouses, distilleries, and all kinds of
factories which provide a steady heat together with a supply of
something eatable. Cold is the only check, and an unwarmed
room during an English winter is more than they can endure.
They are strictly nocturnal, and shun the light, although when
long unmolested they become bolder. The flattened body
enables the Cockroach to creep into very narrow crevices, and
during cold weather it takes refuge beneath the flags of a
kitchen floor, or in other very confined spaces. .

The Cockroach belongs to a miscellaneous group of animals,
which may be described as in various degrees parasitic upon
men. These are all in a vague sense domestic species, but have
not, like the ox, sheep, goat, or pig, been forcibly reduced to
servitude; they have rather attached themselves to man in
various degrees of intimacy. The dog has slowly won his place
as our companion ; the cat is tolerated and even caressed, but
her attachment is to the dwelling and not to us ; the jackal and
rat are scavengers and thieves ; the weasel, jackdaw, and magpie
are wild species which show a slight preference for the neigh-
bourhood of man. All of these, except the cat, which holds a
very peculiar place, possess in a considerable degree qualities
which bring success in the great competitive examination.
They are not eminently specialised, their diet is mixed, their
range as natural species is wide. Apart from man, they would
have become numerous and strong, but those qualities which fit
them so well to shift for themselves, have had full play in the
dwellings of a wealthy and careless host. Of these domestic
parasites at least two are insects, the House-fly and the Cock-
roach; and the Cockroach in particular is eminent in its peculiar
sphere of activity. The successful competition of Cockroaches
with other insects under natural conditions is sufiiciently proved
by the fact that about nine hundred species have already been
described,* while their rapid multiplication and almost world-
wide dissemination in the dwellings of man is an equally
striking proof of their versatility and readiness to adapt them-
selves to artificial circumstances. In numerical frequency they

: British Museum Catalogue of Blattariae (1868) and Supplement (1869). It is
probable that the number is over-estimated in this catalogue, the same species being
occasionally renamed.

22 THE COCKROACH :

probably exceed all domestic animals of larger size, while in
geographical range the five species, lapponica, germanica,
orientali^, americana, and australasice, are together comparable to
the dog or pig, which have been multiplied and transported by
man for his own purposes, and which cover the habitable globe.

The Cockroach a persistent type.

The Cockroach is historically one of the most ancient, and
structurally one of the most primitive, of our surviving insects.
Its immense antiquity is shown by the fact that so many Cock-
roaches have been found in the Coal Measures, where about
eighty species have been met with. The absence of well-defined
stages of growth, such as the soft-bodied larva or inactive pupa,
the little specialised wings and jaws, the simple structure of the
thorax, the jointed appendages carried on the end of the
abdomen, and the unconcentrated nervous system, are marks of
the most primitive insect-types. The order Orthoptera is un-
deniably the least specialised among winged insects at least, and
within this order none are more simple in structure, or reach
farther back in the geological record than the Cockroaches.
The wingless Thysanura are even more generalised, but their
geological history is illegible.*

Life-History.

The eggs of the Cockroach are laid sixteen together in a
large horny capsule. This capsule is oval, with roundish ends,
and has a longitudinal serrated ridge, which is uppermost while
in position within the body of the female. The capsule is
formed by the secretion of a " colleterial ' gland, poured out
upon the inner surface of a chamber (vulva) into which the
oviducts lead. The secretion is at first fluid and white, but
hardens and turns brown on exposure to the air. In this way a
sort of mould of the vulva is formed, which is hollow, and opens
forwards towards the outlet of the common oviduct. Eggs are

* Brongniart has just described a Carboniferous Insect which he considers a
Thysanuran (Dasyleptus Lucasi), though it has but one anal appendage. See C. R.
Soc. Ect., France, 1885.

ITS NATURAL HISTORY.

now passed one by one into the capsule ; and as it becomes full,
its length is gradually increased by fresh additions, while the
first-formed portion begins to protrude from the body of the
female. When sixteen eggs have descended, the capsule is
closed in front, and after an interval of seven or eight days, is
dropped in a warm and sheltered crevice. In Periplaneta
orient alls it measures about *45 in. by '25 in. (fig. 5). The ova

Fig. 5. — Egg-capsule of P. orientalis (magnified). A, external view ;

B, opened ; C, end view.

develop within the capsule, and when ready to escape are of
elongate-oval shape, resembling mummies in their wrappings.
Eight embryos in one row face eight others on the opposite side,
being alternated for close packing. Their ventral surfaces,
which are afterwards turned towards the ground, are opposed,
and their rounded dorsal surfaces are turned towards the wall of
capsule ; their heads are all directed towards the serrated edge.
The ripe embryos are said by Westwood to discharge a fluid
(saliva?) which softens the cement along the dorsal edge, and
enables them to escape from their prison. In Blatta germanica
the female is believed to help in the process of extrication.*
The larvae are at first white, with black eyes, but soon darken.
They run about with great activity, feeding upon any starchy
food which thev can find.

The larvae of the Cockroach hardly differ outwardly from the
adult, except in the absence of wings. The tenth tergum is
notched in both sexes, as in the adult female. The sub-anal
styles of the male are developed in the larva.

Cornelius, in his Beitrage zur nahern Kenntniss von Peri-
planeta orientalis (1853), gives the following account of the moults

* Hummel, loc. cit.

THE COCKROACH :

of the Cockroach. The first change of skin occurs immediately
after escape from the egg-capsule, the second four weeks later,
the third at the end of the first year, and each succeeding moult
after a year's interval. At the sixth moult the insect becomes
a pupa,* and at the seventh (being now four years old) it
assumes the form of the perfect Insect. The changes of skin

Fig. 6.— Young nymph (mule). X 0.

are annual, and like fertilisation and oviposition, take place in
the summer months only. He tells us further that the ova
require about a year for their development. These statements
are partly based upon observation of captive Cockroaches, and
are the only ones accessible ; but they require confirmation by
independent observers, especially as they altogether differ from
Hummers account of the life-history of Blatta germanica, and
are at variance with the popular belief that new generations of
the Cockroach are produced with great rapidity.

The antennae of the male nymph resemble those of the adult
female. Wings and wing-covers appear first in the later larval

* The use of the term pupa to denote the last stage before the complete assump-
tion of wings in the Cockroach, is liable to mislead. There is no resting-stage at all ;
wings are developed gradually, and are nearly as conspicuous in the last larval state
as in the so-called pupa. There seems no reason for speaking of pupre in this case.

It is preferable to designate as "nymphs" young and active Insects, immature
sexually, but with mouth-parts like those of the adult. See Lubbock, Linn. Trans.,
1863, and Eaton, Linn. Trans., 1883.

ITS NATURAL HISTORY.

stages, but are then rudimentary, and constitute a mere pro-
longation of the margins of the thoracic rings. Cornelius says
that the round white spot internal to the antenna first appears
plainly in the pupa, but we have readily found it in a very
young larva. The Insect is active in all its stages, and is

Fig. 7.— Older nymph (male) with rudiments of wings. X 2|.

therefore, with other Orthoptera, described as undergoing
" incomplete metamorphosis." After each moult it is for a few
hours nearly pure white. Of the duration of life in this species
we have no certain information, and there is great difficulty in
procuring any.

Sexual Differences.

Male Cockroaches are readily distinguished from the females
by the well-developed wings and wing-covers. They are also
slighter and weaker than the females ; their terga and sterna
are not so much thickened ; their alimentary canal is more
slender, and they feed less greedily (the crop of the male is
usually only half- full of food). They stand higher on their legs
than the females, whose abdomen trails on the ground. The
external anatomical differences of the sexes may be tabulated
thus : —

THE COCKROACH :

Female.

Antenna shorter than the body,
the third joint longer than
the second.

Wings and wing-covers rudi-
mentary.

Mesosternum divided.
Abdomen broader.

Terga 8 and 9 not externally
visible.

The 10th tergum notched.

The 7th sternum divided be-
hind.

The external outlet of the
rectum and vulva between
the 10th tergum and the
7th sternum.

No sub- anal stvles.

Male.

Antenna rather longer than
the body, the third joint
about as long as the second.

Wings and wing-covers well
developed.

Mesosternum entire.
Abdomen narrower.
Terga 8 and 9 externally visible.

tergum

hardly

The 10th
notched.

The 7th sternum undivided.

The outlet between the 10th
tergum and the 9th sternum.

Sub-anal styles.

Parasites.

We have before us a long list of parasites* which infest the
Cockroach. There is a conferva, an amoeba, several infusoria,
nematoid worms (one of which migrates to and fro between the
rat and the Cockroach), a mite, as well as hymen opterous and
coleopterous Insects. The Cockroach has a still longer array of
foes, which includes monkeys, hedgehogs, pole-cats, cats, rats,
birds, chamseleons, frogs, and wasps, but no single friend, unless
those are reckoned as friends which are the foes of its foes.

Names in common use.

A few lines must be added upon the popular and scientific
names of this insect. Etymologists have found it hard to
explain the common English name, which seems to be related to

* See Appendix.

ITS NATURAL HISTORY. 27

cock and roach, but has really nothing to do with either. The
lexicographers usually hold their peace about it, or give deriva-
tions which are absurd. Mr. James M. Miall informs us that
" CockroacJi can be traced to the Spanish cucardcha, a diminutive
form of cuco or coco (Lat. coccum, a berry). Cucardcha is used
also of the woodlouse, which, when rolled up, resembles a berry.
The termination -dcha (Ital. -accio, -accia) signifies mean or
contemptible. The Spanish word has also taken a French form ;
at least coqueraches has some currency (see, for example, Tylor's
Anahuac, p. 325)." In provincial English Black Clock is a com-
mon name. The German word Schabe, often turned into
Schwab e, means perhaps Suabian, as Moufet, quoting Cordus,
seems to explain.* Fmnzose and Dane are other German words
for the insect, applied specially to Blatta germanica ; and all
seem to imply some popular theory as to the native country of
the Cockroach.f This etymology of Schabe is not free from
suspicion, particularly as the same term is commonly applied to
the clothes-moth. Kakerlac, much used in France and French-
speaking colonies, is a Dutch word of unknown signification.
P. Americana is usually named Kakerlac or Cancrelat by the
French; while orient alls has many names, such as Cafard, Ravet,
and Bete noire.% The name Blatta was applied by the ancients
to quite different insects, of which Virgil and Pliny make
mention ; Periplaneta is a modern generic term, coined by
Burmeister.

Uses.

Of the uses to which Cockroaches have been put we have
little to say. They constitute a popular remedy for dropsy in
Russia, and both cockroach-tea and cockroach-pills are known
in the medical practice of Philadelphia. Salted Cockroaches
are said to have an agreeable flavour which is apparent in
certain popular sauces.

* Insectorum Theatnim, p. 138. The name Sclnvabe is frequent in Franconia,
where it is "believed to have taken origin. Suabia adjoins Franconia, to the south.

"1* Compare the Swedish name (supra, p. 18).

I A fuller list of vernacular names is given by Eolland, Faune Populaire de la
France, Vol. III., p. 285. See also Nennich, Polyglotten Lexicon, VTol. L, p. 620.

CHAPTER IV.

THE OUTER SKELETON.

SPECIAL REFERENCES.

KKUKENBERG. Vergleichend-Physiologische Vortriige. IV. — Vergl. Physiologic
<ler Thierischen Geriistsubstanzen. (1885.) [Chemical Relations of Chitin.]

GRABEK. Ueber eine Art fibrilloiden Bindegewebes der Insectenhaut. Arch. f.
mikr. Anat. Bd. X. (1874.) [Minute Structure of Integument.] Also,

VIALLANES. Recherches sur THistologie des Insectes. Ann. Sci. Nat., Zool.
VP Serie, Tom. XIV. (1882).

AUDOUIN. Recherches anatomiques sur le thorax des Insectes, &c. Ann. Sci. Nat.
Tom. I. (1824.) [Theoretical Composition of Insect Segments.] Also,

MILNE-EDWARDS. Lemons sur la Physiologic et TAnatomie Comparee. Tom. X.
(1874.)

SAVIGNT. Memoires sur les animaux sans vertebres. Partie Ic- Theorie des
organes de la bouche des Crustacees et des Insectes. (1816.) [Comparative
Anatomy of the Mouth-parts.]

MUHR. Ueber die Mundtheile der Orthopteren. Prag. 1877. [Mouth-parts of
Orthoptera.]

Cliitin.

WHEN the skin of an Insect is boiled successively in acids,
alkalies, alcohol, and ether, an insoluble residue known as
Chitin (CisH^NsOio) is obtained. It maybe recognised and
sufficiently separated by its resistance to boiling liquor potassse.
Chitin forms less than one-half by weight of the integument, but
it is so coherent and uniformly distributed that when isolated
by chemical reagents, and even when cautiously calcined, it
retains its original organised form. The colour which it fre-
quently exhibits is not due to any essential ingredient ; it may
be diminished or even destroyed by various bleaching processes.
The colouring- matter of the chitin of the Cockroach, which is
amber-yellow in thin sheets and blackish-brown in dense
masses, is particularly stable and difficult of removal. Its com-
position does not appear to have been ascertained ; it is white
when first secreted, but darkens on exposure to air. Fresh-

THE COCKROACH : ITS OUTER SKELETOX. 29

moulted Cockroaches are white, but gradually darken in three
or four hours. Lowne* observes that in the Blow-fly the pig-
ment is " first to be met with in the fat-bodies of the larvae.
These are perfectly white, but when cut from the larva, and
exposed to the air, they rapidly assume an inky blackness.
. When the perfect insect emerges from the pupa, and
respiration again commences, the integument is nearly white,
or a faint ashy colour prevails. This soon gives place to the
characteristic blue or violet tint, first immediately around those
portions most largely supplied with air vessels." Professor
Moseleyf tells us that, thinking it just within the limits of
possibility that the brown coloration of the Cockroach might be
due to the presence of silver, he analysed one pound weight of
Blatta. He found no silver, but plenty of iron, and a remark-
able quantity of manganese. That light has some action upon
the colouring matter seems to be indicated by the fact that in a

newly-moulted Cockroach the dorsal surface darkens first.

Chitin is not peculiar to Insects, nor even to Arthropoda.
The pen of cuttle-fishes and the shell of Lingula contain the
same substance,^ which is also proved, or suspected, to occur in
many other animals.

The chemical stability of chitin is so remarkable that we
might well expect it to accumulate like the inorganic con-
stituents of animal skeletons, and form permanent deposits.
Schlossberger§ has, however, shown that it changes slowly
under the action of water. Chitin kept for a year under water
partially dissolved, turned into a slimy mass, and gave off a
peculiar smell. This looks as if it were liable to putrefaction.
The minute proportion of nitrogen in its composition may
explain the complete disappearance of chitin in nature.

The Chitinous Cuticle.

The chitinous exoskeleton is rather an exudation than a true
tissue. It is not made up of cells, but of many superposed

* Anatomy of the Blow-fly, p. 11.
t Q. J. Micr. Sci., 1871, p. 394.

£ Krukeaberg. Yergl. Physiologische Vortriige, p. 200. Halliburton, Q. J. Micr.
Sci., 1885, p. 173.

§ Ann. d. Chem. u. Pharm., Bd. 98.

THE COCKROACH :

laminae, secreted by an underlying epithelium, or " chitino-
genous layer." This consists of a single layer of flattened cells,
resting upon a basement membrane. A cross-section of the
chitinous layer, or "cuticle," examined with a high power

677*

Fig. 8. — Diagram of Insect integument, in section, bm, basement membrane ;
hyp, hypodermis, or chitinogenous layer ; ct, ct', chitinous cuticle ; s, a seta.

shows extremely close and fine lines perpendicular to the laminae.
The cells commonly form a mosaic pattern, as if altered in
shape by mutual pressure. The free surface of the integument
of the Cockroach is divided into polygonal, raised spaces. Here
and there an unusually long, flask-shaped, epithelial cell projects
through the cuticle, and forms for itself an elongate chitinous
sheath, commonly articulated at the base ; such hollow sheaths
form the hairs or setae of Insects — structures quite different
histologically from the hairs of Vertebrates.

The polygonal areas of the cuticle correspond each to a
chitinogenous cell. Larger areas, around which the surrounding
ones are radiately grouped, are discerned at intervals, and these
carry hairs, or give attachment to muscular fibres.

Viallanes (loc. cit.) has added some interesting details to what
was previously known of Insect-hairs. There are, he points
out, two kinds of hairs, distinguished by their size and struc-
ture. The smaller spring from the boundary between contiguous
polygonal areas, and have no sensory character. The larger
ones occupy unusually large areas, surmount chitinogenous cells
of corresponding size, and receive a special nervous supply.

ITS OUTER SKELETON.

The nerve* expands at the base of the hair into a spindle-
shaped, nucleated mass (bipolar ganglion-cell), from which issues
a filament which traverses the axis of the hair, piercing the
chitinogenous cell, whose protoplasm surrounds it with a sheath
which is continued to the tip of the hair. Such sensory hairs
are abundant in parts which are endowed with special sensibility.

Fig. 9. — Nerve -ending in skin of Stratiomys larva, h, hairs; b, their chitinous
base; c, nucleus of generating cell; y, ganglion cell, x 250. Copied
from Viallanes.

Fig. 10. — Diagram of sensory hair of Insect. Cc, chitinous cuticle ; h, hair ; c, its
generating cell ; g, ganglion cell ; bm, basement-membrane.

The chitinous cuticle is often folded in so as to form a deep
pit, which, looked at from the inside of the body, resembles a
lever, or a hook. Such inward-directed processes serve chiefly
for the attachment of muscles, and are termed apodemes (apode-
matci). A simple example is afforded by the two glove-tips
which lie in the middle line of the under-surface of the thorax
(p. 58, and fig. 27). In other cases the pit is closed from the

* Previously observed by Leydig in Corethra.

32 THE COCKROACH :

first, and the apodeme is formed in the midst of a group of
chitinogenous cells distant from the superficial layer, though
continuous therewith. Many tendons of insertion are formed
in this way. The two forked processes in the floor of the thorax
(p. 58, and fig. 27) are unusually large and complex structures of
the same kind. In the tentorium of the head (p. 39, and fig. 17)
a pair of apodemes are supposed to unite and form an extensive
platform which supports the brain and gullet.

Fig. 11. — Nymph (in last larval stage) escaping from old skin. X 2|.

Like other Arthropoda, Insects shed their chitinous cuticle
from time to time. A new cuticle, at first soft and colourless, is
previously secreted, and from it the old one gradually becomes
detached. The setae probably serve the same purpose as the
" casting-hairs ' described by Braun in the crayfish, and by
Cartier in certain reptiles,* that is, they mechanically loosen the
old skin by pushing beneath it. In many soft-bodied nymphs
the new skin can be gathered up into a multitude of fine
wrinkles, which facilitate separation, but we have not found
such wrinkles in the Cockroach, except in the wings. The
integument about to be shed splits along the back of the
Cockroach, from the head to the end of the thorax,*f* and the
animal draws its limbs out of their discarded sheaths with much
effort. It is remarkable that the long, tapering, and many-
jointed antennae are drawn out from an entire sheath. At the

* A condensed and popular account of these researches will be found in Semper's
Animal Life, p. 20.

+ Prof. Huxley (Anat. Invert. Animals, p. 419) states that the integument splits
along the abdomen also, but this is a mistake.

ITS OUTER SKELETON.

same time the chitinous lining of the tracheal tubes is cast,
while that of the alimentary canal is broken up and passed

through the body.

Fig. 12. — Cast skin of older nymph ("pupa"). X 2|.

Prolonged boiling in caustic potash, though it dissolves the
viscera, does not disintegrate the exoskeleton. This shows that
the segments of the integument are not separate chitinous
rings, but thickenings of a continuous chitinous investment.
Nevertheless, their constancy in position and their conformity
in structure often enable us to trace homologies between different
segments and different species as certainly as between corres-
ponding elements of the osseous vertebrate skeleton.

Parts of a Somite.

Audouin's laborious researches into the exoskeleton of Insects*
resulted in a nomenclature which has been generally adopted.
He divides each somite (segment) into eight pieces, grouped in
pairs — viz., terga (dorsal plates), sterna (ventral plates), epimera
(adjacent to the terga), and epi*terna (adjacent to the sterna).

While admitting the usefulness of these terms, we must warn
the reader not to suppose that this subdivision is either normal
or primitive. The eight-parted segment exists in no single

* Audouin. Kech. anat. sur le thorax des Insectes, &c. (Ann. Sci. Nat., Tom I.,
p. 97. 1824.)

34 THE COCKROACH :

larval or adult Arthropod. Lower forms and younger stages
take us further from such a type, instead of nearer to it ; and
Audouin's theoretical conception is most fully realised in the
thorax of an adult Insect with well-developed legs and wings.

The morphologist would derive all the varieties of Arthropod
segments from the very simple and uniform chitinous cuticle
found in Annelids and many Insect-larvae. This becomes
differentiated by unequal thickening and folding in, and a series
of rings connected by flexible membranes is produced. Loco-
motive and respiratory activity commonly lead to the definition
of terga and sterna, which are similarly attached to each other
by flexible membranes. A pair of limbs may next be inserted
between the terga and sterna, and the simple segment thus
composed occurs so extensively in the less modified regions
and in early stages that it may well be considered the typical
Arthropod somite.

Special needs may lead to the division of the sterna into
lateral halves, but this is purely an adaptive change. The
third thoracic sternum of the male Cockroach, and the second
and third of the female are thus divided, as is also the hinder
part of the seventh abdominal sternum of the female.

In an early stage every somite has its tergal region divided
into lateral halves, owing to the late completion of the body on
this side. Traces of this division may survive even in the
imago. There is often a conspicuous dorsal groove in the
thoracic terga, and at the time of moult the terga split along
an accurately median line (see fig. 12).

Additional pieces may be developed between the terga and
sterna, and these have long been termed pleural.* There may
be, for example, single stigmatic plates, as in the abdomen of
the Cockroach, pieces to support the thoracic legs, and pieces to
support the wings ; but the number and position of these plates
depends upon their immediate use, and their homologies become
very uncertain when Insects of different orders are compared.
In general, the pleural elements of the segment are late in
development, variable, and highly adaptive.

This application of the word to denote parts intermediate between terga and
sterna has become general since its adoption by Audouin. It appears also in the
older and deservedly obsolete nomenclature of Kirby and Spence. Professor Huxley
has unfortunately disturbed the consistent use of this term by giving the name
pleura to the free edges of the terga in Crustacea.

ITS OUTER SKELETON. 35

Somites of the Cockroach.

The exoskeleton of the Cockroach is divisible into about
seventeen segments, which are grouped into three regions, as
follows : —

TT -I f Procephalic lobes

' ( Post-oral segments ... 3

Thorax ... ... ... ... 3*

Abdomen ... ... ... ... 11

It is a strong argument in favour of this estimate that many
Insects, at the time when segmentation first appears, possess
seventeen segments. f The procephalic lobes, from which a great
part of the head, including the antennae, is developed, are often
counted as an additional segment.^:

The limbs, which in less specialised Arthropoda are carried
with great regularity on every segment of the body, are greatly
reduced in Insects. Those borne by the head are converted into
sensory and masticatory organs ; those on the abdomen are
either totally suppressed, or extremely modified, and only the
thoracic limbs remain capable of aiding in locomotion.

The primitive structure of the Arthropod limb is adapted to
locomotion in water, and persists, with little modification, in
most Crustacea. Here we find in most of the appendages § a
basal stalk (protopodite), often two-jointed, an inner terminal
branch (endopodite), and an outer terminal branch (exopodite),
each of the latter commonly consisting of several joints. It
does not appear that the appendages of Insects conform to the
biramous Crustacean type, though the ends of the maxillae are
often divided into an outer and an inner portion.

We shall now proceed to describe, in some detail, the regions
of the body of the adult Cockroach.

* Where the thorax apparently consists of four somites, as in some Hymenoptera,
Hemiptera, Coleoptera, and Lepidotera, the first abdominal segment has become
blended with it.

t Balfour. Embryology, Vol. I., p. 337.

£ E.g., by Graber. Insekten, Vol. II., p. 423.

§ See, for example, Huxley on the Crayfish.

THE COCKROACH :

Head; Central Parts.

The head of the Cockroach, as seen from the front, is pear-
shaped, having a semi-circular outline above, and narrowing
downwards. A side-view shows that the front and back are
flattish, while the top and sides are regularly rounded. In the

Fig. 13.— Front of Head.

XlO.

living animal the face is usually inclined downwards, but it can
be tilted till the lower end projects considerably forward. The
mouth, surrounded by gnathites or jaws, opens below. On the
hinder surface is the occipital foramen, by which the head com-
municates with the thorax. A rather long neck allows the
head to be retracted beneath the pronotum (first dorsal shield
of the thorax) or protruded beyond it.

On the front of the head we observe the clypeus, which
occupies a large central tract, extending almost completely
across the widest part of the face. It is divided above by a
sharply bent suture from the two epicranial plates, which form
the top of the head as well as a great part of its back and sides.
The labrum hangs like a flap from its lower edge. A little
above the articulation of the labrum the width of the clypeus is
suddenly reduced, as if a squarish piece had been cut out of
each lower corner. In the re-entrant angle so formed, the
ginglymus, or anterior articulation of the mandible, is situated.

The labrum is narrower than the clypeus, and of squarish
shape, the lower angles being rounded. It hangs downwards,

ITS OUTER SKELETON.

with a slight inclination backwards towards the mouth, whose
front wall it forms. On each side, about halfway between the
lateral margin and the middle line, the posterior surface of the
labrum is strengthened by a vertical chitinous slip set with
large setae. Each of these plates passes above into a ring, from
the upper and outer part of which a short lever passes upwards,
and gives attachment to a muscle (levator menfi).

Fig. 14. — Top of Head, cp, epicranial plate ; oc, eye ; ye, gena. X 10.

The top and back of the head are defended by the two
epicranial plates, which meet along the middle line, but diverge
widely as they descend upon the posterior surface, thus enclosing
a large opening, the occipital foramen. Beyond the foramen,
they pass still further downwards, their inner edges receding in
a sharp curve from the vertical line, and end below in cavities
for the articulation of the mandibular condvles.*

Fig. 15. — Side of Head, oc, eye ; ge, gena ; inn, mandible. X 10.

* One of the few points in which we have to differ from the admirable description
of the Cockroach given in Huxley's Comparative Anatomy of Invertebrated
Animals, relates to the articulation of the mandible, which is there said to be
carried by the gena.

THE COCKROACH :

The sides of the head are completed by the eyes and the
genge. The large compound eye is bounded above by the
epicranium ; in front by a narrow band which connects the
epicranium with the clypeus ; behind, by the gena. The gena
passes downwards between the eye and the epicranial plate,
then curves forwards beneath the eye, and just appears upon
the front of the face, being loosely connected at this point with
the clypeus. Its lower edge overlaps the base of the mandible,
and encloses the extensor mandibulsB.

The occipital foramen has the form of an heraldic shield. Its
lateral margin is strengthened by a rim continuous with the
tentorium, or internal skeleton of the head. Below, the fora-
men is completed by the upper edge of the tentorial plate,

Fig. 16. — Back of Head, ca, cardo ; st, stipes ; ga, galea ; la, lacinia ; pa, palp ;
sm, subrnentum ; ra, nientum ; pg, paraglossa. X 10.

which nearly coincides with the upper edge of the submentum
(basal piece of the second pair of maxillce) ; a cleft, however,
divides the two, through which nerve-commissures pass from
the sub-cesophageal to the first thoracic ganglion. Through the
occipital foramen pass the oesophagus, the salivary ducts, the
aorta, and the tracheal tubes for the supply of air to the head.

The internal skeleton of the head consists of a nearly trans-
parent chitinous septum, named tentorium by Burmeister, which
extends downwards and forwards from the lower border of the

ITS OUTER SKELETON.

occipital foramen. In front it gives off two long crura, or
props, which pass to the ginglymus, and are reflected thence
upon the inner surface of the clypeus, ascending as high as the
antennary socket, round which they form a kind of rim. Each
crus is twisted, so that the front surface becomes first internal

and then posterior as it passes towards the ctypeus. The form
of the tentorium is in other respects readily understood from

Fig. 17- — Fore-half of Head, with tentorium, seen from behind, x 12.

the figure (fig. 17). Its lower surface is strengthened by a
median keel which gives attachment to muscles. The oesophagus
passes upwards between its anterior crura, the long flexor of the
mandible lies on each side of the central plate ; the supra-
cesophageal ganglion rests on the plate above, and the sub-
cesophageal ganglion lies below it, the nerve-cords which unite
the two passing through the circular aperture. A similar
internal chitinous skeleton occurs in the heads of other Orthop-
tera, as well as in Neuroptera and Lepidoptera. Palmen* thinks
that it represents a pair of stigmata or spiracles, which have
thus become modified for muscular attachment, their respiratory
function being wholly lost. In Ephemera he finds that the
tentorium breaks across the middle when the skin is changed,
and each half is drawn out from the head like the chitinous
lining of a tracheal tube.

* Morphologic des Tracheen-systems, p. 103.

THE COCKROACH :

Antenna; Eyes.

A pair of antennoe spring from the front of the head. In the
male of the common Cockroach they are a little longer than
the body ; in the female rather shorter. From seventy-five
to ninety joints are usually found, and the three basal joints are
larger than the rest. Tip to about the thirtieth, the joints are

Fig. 18. — Base of Antenna of Male (to left) and Female (to right). X 24.

about twice as wide as long ; from this point they become more
elongate. The joints are connected by flexible membranes, and
provided with stiff, forward-directed bristles. The ordinary
position of the antennae is forwards and outwards.

Each antenna is attached to a relatively large socket (fig. 15),
which lies between the epicranium and clypeus, to the front and
inner side of the compound eyes. A flexible membrane unites
the antenna to the margin of the socket, from the lower part of
which a chitinous pin projects upwards and supports the basal
joint.

It is well known that in many Crustacea two pairs of antennae
are developed, the foremost pair (antennules) bearing two com-
plete filaments. Some writers have suggested that both pairs
may be present in Insects, though not simultaneously, the
Crustacean antennule being found in the larva, and the Crus-
tacean antenna in the adult. This view was supported by the

ITS OUTER SKELETON. 41

familiar fact that in many larvae the antennae are placed further
forward than in the adult. The three large joints at the base
of Orthopterous antennae have been taken to correspond with
those of Crustacean antennules, and it has been inferred that in
Insects with incomplete metamorphosis, only antennules or
larval antennae are developed.* This reasoning was never very
cogent, and it has been impaired by further inquiry. Weismann
has shown that in Corethra plumicomis, the adult antenna,
though inserted much further back than that of the larva, is
developed within it,t and Graber has described a still more
striking case of the same thing in a White Butterfly.:}: There
is, therefore, no reason to suppose that Insects possess more than
one pair of antennae, which is probably preoral, not correspond-
ing with either of the Crustacean pairs.

We have already noticed (p. 26) the superficial points in
which the antenna of the male Cockroach differs from that of
the female.

The eyes of some Crustacea are carried upon jointed appen-
dages, but this is never the case in Insects, though the eye-
bearing surface may project from the head, as in Diopsis and
Stylops. Professor Huxley § supposes that the head of an Insect
may contain six somites, the eyes representing one pair of
appendages. The various positions in which the eyes of Arthro-
poda may be developed weakens the argument drawn from the
stalk-eyed Crustacea. Claus and Fritz M tiller go so far on the
other side as to deny the existence of an eye-segment even in
Crustacea.

Mouth-parts of the Cockroach.

Before entering upon a full description of the mouth-parts of
the Cockroach, which present some technical difficulties, the
beginner in Insect anatomy will find it useful to get a few
points of nomenclature fixed in his memory. Unfortunately,
the terms employed by entomologists are at times neither
convenient nor philosophical.

* Zaddach, Entw. des Phryganiden Eies, p. 86 ; Rolleston, Forms of Animal Life,
p. 75, &c.

t Zeits. f. wiss. Zool., Bd. XVI., pi. vii., fig. 33.

J Insekten, Vol. II., p. 508.

§ Anat. Invert. Animals, p. 398.

42 THE COCKROACH :

There are three pairs of jaws, disposed behind the labrum, as

in the diagram : —

LABRUM.

1st pair of Jaws (MANDIBLES).

2nd ,, (MAXILLAE).

3rd ,, (LABIUM, or 2nd pair of Maxillae).

Fig. 19. — Diagram of Cockroach Jaws, iii horizontal section.

The mandible is undivided in all, or nearly all, Insects. Each
maxilla may consist of

A palp on the outer side,

A gaka (hood),

A lacmia (blade), on the inner side.

The galea (hood) of the 3rd pair of jaws is sometimes called
the paraglossa.

A tongue-like process may be developed from the front wall
of the mouth (epipharynx) , or from the back wall (hypopharynx
or lingua)* Both epipharynx and hypopharynx project into
the mouth, and, in some Diptera, far be}rond it.

The tip of the labium is sometimes produced into a long
tongue, called the ligula (strap).

The mouths of Insects may be classed as : —

BITING. — Orthoptera, Neuroptera, Coleoptera (in some
Coleoptera a licking tongue is developed), most
Hymenoptera.

LICKING AND SUCKING. — Some Ifymenoptera — e.g., Honey
Bee.

SUCKING. — (a) With lancets — Diptera, Hemiptera.
(b) Without lancets — Lepidoptera.

* Professor Huxley has proposed to call the attached base hypopharynx, and the
free tip lingua.

ITS OUTER SKELETON.

The reference of these to a common plan, and the determina-
tion of the constituent parts, is mainly the work of Savigny.
Mouth-parts were made the basis of the classification of Insects
by Fabricius (1745-1808).

MTI

Fig. 20. — The Jaws, separated. Mn, mandible, seen from behind (to left) and front
(to right) ; Mxl maxilla (first pair) ; Mxn labiuni, or second pair of
maxilla?. The other letters as before. X 20.

44 THE COCKROACH :

The mandibles of the Cockroach are powerful, single-jointed*
jaws, each of which is articulated by a convex "condyle" to the
lower end of the epicranial plate, and again by a concave
" ginglymus" to the clypeus. The opposable inner edges are
armed with strong tooth-like processes of dense chitin, which
interlock when the mandibles close ; those towards the tip of
the mandible are sharp, while others are blunt, as if for crush-
ing. Each mandible can be moved through an angle of about
30°. A flexible chitinous flap extends from its inner border to
the labrum. The powerful flexor of the mandible arises within
the epicranial vault ; its fibres converge to a chitinous tendon,
which passes outside the central plate of the tentorium, and at
a lower level through a fold on the lower border of the clypeus,
being finally inserted near the ginglymus. A short flexor arises
from the crus of the tentorium. The extensor muscle arises
from the side of the head, passes through the fold formed by
the lower end of the gena, and is inserted close to the outer side
of the condyle of the mandible.

The anterior maxilla) lie behind the mandibles, and like them
are unconnected with each other. They retain much more of
the primitive structure of a gnathite than the mandibles, in
which parts quite distinct in the maxilke are condensed or
suppressed. The constituent pieces are seen in fig. 20. There
is a two-jointed basal piece, consisting of the cardo (ca) and the
stipes (st). The cardo is a transverse plate bent upon itself, and
enclosing muscles; it is attached to the outward-directed pedicel
of the occipital frame, and carries the vertical stipes. To the
side and lower end of the stipes is attached the five-jointed
palp (pa), a five-jointed limb used in feeding and in exploration,
while the lacinia (la) and galea (go) are articulated to its
extremity. The lacinia is internal and posterior to the galea ;
it is broad above, but narrows below to a bifid tooth of dense
chitin ; its inner surface is beset with a cluster of strong setae.
The galea is more flexible, and forms an irregular three-cornered

* Professor J. "Wood-Mason points out that in Machilis (one of the Thysanura) the
mandible shows signs of segmentation, while the apical portion is deeply divided into
an inner and an outer half. Ripe embryos of Panesthia (Blatta) javanica are said to
exhibit folds which indicate the consolidation of the mandible out of separate joints,
while the cutting and crushing portions of the edge are divided by a "sutural mark,"
which may correspond to the line of junction of the divisions of a biramous appen-
dage (Trans. Ent. Soc., 1879, pt. 2, p. 145).

ITS OUTER SKELETON. 45

prism with an obliquely truncated end, upon which are many
fine hairs. A flexible and nearly transparent flap connects the
inner edges of the stipes and cardo, and joins both to the
labium. The muscles which move the bases of the maxillae
spring from the crura, central plate, and keel of the tentorium.

On the posterior surface of the head, below the occipital
foramen, we find a long vertical flap, the labium, which extends
downwards to the opening of the mouth. It represents a
second pair of maxillre, fused together in their basal half, but
retaining elsewhere sufficient resemblance to the less modified
anterior pair to permit of the identification of their component
parts. The upper edge is applied to the occipital frame, but is
neither continuous with that structure nor articulated thereto.
By stripping off the labium upwards it may be seen that it is
really continuous with the chitinous integument of the neck.
The broad shield-like base is incompletely divided by a trans-
verse hinge into an upper and larger piece, the submentiim, and
a distal piece, the men turn. To the mentum are appended
representatives of the galese (here named paraglossa) and laciniae,
while a three-jointed palp with an additional basal joint (dis-
tinguished as the palpiger) completes the resemblance to the
maxilla3 of the first pair.* In front of the labium, and lying
in the cavity of the mouth is a chitinous fold of the oral
integument, the lingua, which lies like a tongue in the floor of
the mouth. The common duct of the salivary glands enters the
lingua, and opens on its hinder surface. The lingua is supported
by the chitinous skeleton represented in the figures of the
salivary glands. (Chap, vii., infra.)

The epipharynx, which is a prominent part in Coleoptera and
Diptera, is not recognisable in Orthoptera.

Functions of the Antennce and Mouth-parts.

We must now shortly consider the functions of the parts just
described. The antennoo have long been regarded as sense-
organs, and even the casual observer can hardly fail to remark
that they are habitually used by the Insect to gain information

* The homology of the labium with the first pair of maxillae is in no other Insects
so distinct as in the Orthoptera.

46 THE COCKROACH :

concerning its immediate surroundings. Long antennae, such
as those of the Cockroach, are certainly organs of touch, but it
has been much disputed whether they may not also be the seat
of some special sense, and if so, what that sense may be.
Several authors have found reason to suppose that in the Insect-
antenna resides the sense of hearing, but no evidence worth the
name is forthcoming in favour of this view. Much better
support can be found for the belief that the antenna is an
olfactory organ,* and some experiments which seem conclusive
on this point will be cited in a later chapter.

In the Cockroach the mandibles and maxillae are the only
important instruments of mastication. The labium is indirectly
concerned as completing the mouth behind and supporting the
lingua, which is possibly of importance in the ordinary opera-
tions of feeding. Plateauf has carefully described the mode of
mastication as observed in a Carabus, and his account seems to
hold good of biting Insects in general. The mandibles and
maxillae act, as he tells us, alternately, one set closing as the
others part. The maxillae actually push the morsel into the
buccal cavity. When the mandibles separate, the head is
slightly advanced, so that the whole action has some superficial
resemblance to that of a grazing quadruped.

The palps of the maxillae and labium have been variously
regarded as sensory and masticatory instruments. Not a few
authors believe that they are useful in both ways. The question
has lately been investigated experimentally by Plateau, f who
finds that removal of both maxillary and labial palps does not
interfere either with mastication or the choice of food. He
observes that in the various Coleoptera and Orthoptera sub-
mitted to experiment the palps are passive while food is being
passed into the mouth.

Plateau's experiments are conclusive as to the subordinate
value of the palps in feeding. The observation of live Cock-

•

* Rosenthal, Ueb. d. Geruchsinn cler Insekten. Arch. f. Phys. Reil u. Autenrieth,
Ed. X. (1811). Hauser, Zeits. f. wiss. Zool., Bd. XXXIV. (1880).

t Mem. Acad. Roy. de Belgique, Tom. XLI. (1874). Prof. Plateau's writings will
often be referred to in these pages. We owe to him the most important researches
into the physiology of Invertebrates which have appeared for many years.

J Exp. sur le Role des Palpes chez les Arthropodes Maxilles. Pt. I. Bull. Soc.
Zool. de France, Tom. X. (1885).

ITS OUTER SKELETON. 47

roaches has satisfied us that the palps are constantly used when
the Insect is active, whether feeding or not, to explore the
surface upon which it moves. "We have seen no ground for
attributing to the palps special powers of perceiving odours or
flavours, nor have we observed that they aid directly in filling
the mouth with food.

It is worthy of note that Leydig has described and figured

ti fc' <j t — j

in the larva of Hydroporus (?), and Hauser in Dytiscus,
Curabits, &c., a peculiar organ, apparently sensor}-, which is
lodged in the maxillary and labial palps. It consists of whitish
spots, sometimes visible to the naked eye, characterised by
unusual thinness of the chitinous cuticle and by the aggregation
beneath it of a crowd of extremely minute sensory rods. Of
this organ no satisfactory explanation has yet been given.*

Comparison of Mouth-parts in different Insects.

The jaws of the Cockroach form an excellent standard of
comparison for those of other Insects, and we shall attempt to
illustrate the chief variations by referring them to this type.f
Mouth-parts are so extensively used in the classification of
Insects that every entomologist ought to have a rational as well
as a technical knowledge of their comparative structure. ]STo
part of Insect anatomy affords more striking examples of
adaptive modification. In form, size, and mode of application
the jaws vary extremely. It would be hard to find feeding-
organs more unlike, at first sight, than the stylets of a Gnat and
the proboscis of a Moth, yet the study of a few well-selected
types will satisfy the observer that both are capable of deriva-
tion from a common plan. Nor is this common plan at all
vague. It is accurately pictured in the jaws of the Cockroach
and other Orthoptera. These correspond so entirely with the
primitive arrangement, inferred by a process of abstraction from

* Ley dig, Taf. z. vergl. Anat., pi. x., fig. 3. Hauser, Zeits. f. wiss. Zool., Bd.
XXXIV., p. 386. Jobert has figured the sensory organs of the maxillary palps of
the Mole-cricket (Ann. Sci. Nat., 1872), and Forel similar organs in Ants (Bull. Soc.
Vaudoise, 1885).

"t* The reader who desires to follow this subject further is recommended to study
chap. vi. of Graber's Insekten, which we have found very useful.

THE COCKROACH :

the most dissimilar Insects, as to furnish a strong argument for
the descent of all higher Insects from forms not unlike Orthop-
tera in the structure of their mouth-parts.

Though the jaws of the Cockroach are eminently primitive
with respect to those of most other Insects, they are themselves
derived from a far simpler arrangement, which is demonstrable
in all embryonic Insects. Fig. 21 shows an Aphis within the

MX'

Fig. 21. — Embryo of Aphis. Copied from Mecznikow, Zeits. f. wiss. Zool.,
Bd. XVI., taf. xxx., fig. 30. References in text. X 220.

egg. The rudiments of the antennae (At), mandibles (Mn\ and
maxilloo (Mis1, Mx2) form simple blunt projections, similar to
each other and to the future thoracic legs (L1, L2, L3). We
see, therefore, that all the appendages of an Insect are similar
in an early stage of growth ; and we may add that a Centipede,
a Scorpion, or a Spider would present very nearly the same
appearance in the same stage. A Crustacean in the egg would
not resemble an Insect or its own parent so closely.* Aquatic
life favours metamorphosis, and most Crustacea do not begin
life with their full quota of legs, but acquire them as they are
wanted.

Paired appendages of perfectly simple form are therefore the
first stage through which all Insect-jaws must pass. Our second
stage is a little more complex, and not nearly so universal as the
first. A caterpillar (fig. 22) has its own special wants, and these
are met by the unequal development of its jaws. The mandibles
are already as complete as those of the Cockroach, which they

* Freshwater Crustacea, however, are sometimes similar to their parents at the
time of hatching.

ITS OUTER SKELETON.

closely resemble, but the maxillaa are stunted cylinders formed
mainly of simple rings, and very like the antennae. They show,
however, the beginnings of three processes (palp, galea, and
lacinia), which are usually conspicuous in well-developed maxillae.
The second pair of maxilloe (Lni) are coalesced, as usual, and

Fig. 22.— Head of larva of Goat Moth, seen from behind.
Copied from Lyonnet.

form the spinneret. The mouth-parts of the Caterpillar do not
therefore in all respects represent a universal stage of develop-
ment, but show important adaptive modifications. The man-
dibles are rapidly pushed forward, and attain their full
development in the larva ; the first pair of maxillrc are tempo-
rarily arrested in their growth, and persist for a long time in a
condition which Orthopterous embryos quickly pass through ;
the maxillae of the second pair are not only arrested in their
growth, but converted to a special use, which seems to stop all
further progress. The labial palps, indeed, which are not at all
developed in the caterpillar, survive, and become important
parts in the moth ; but the greater part of the labium disappears
when the time for spinning the coccoon is over.

We come next to the Orthopterous mouth, which is well
illustrated by the Cockroach. This is retained with little modi-
fication in all the biting Insects (Coleoptera and Neuroptera).
The mandibles may become long and pointed, as in Staphylinus
and other predatory forms ; in some larvoe of strong carnivorous
propensities (Ant-lion, Dytiscus* Chrysopa) they are perforate at

* In Dytiscus the mandibles are perforate at the base, and not at the tip. See
Burgess in Proc. Bost. Soc. Nat. Hist., Vol. XXI., p. 223.

50 THE COCKROACH :

the tip, and through them the juices of the prey are sucked into
the mouth, which has no other opening. The labium undergoes
marked adaptive change, without great deviation from the com-
mon plan, in the "mask" of the larva of the Dragon-fly. This
well-known implement has a rough likeness, in the arrangement
and use of its parts, to a man's fore-limb. The submentum
forms the arm, the mentum the fore-arm. Both these are
simple, straight pieces, connected by an elbow-joint. The hand
is wider, and carries a pair of opposable claws, the paraglossoo.
In some Coleoptera the labium is reduced to a stiff spine, while
in the Stag-beetle it is flexible and hairy, and foreshadows the
licking tongue of the Bee. The maxilla; become long and hairy
in flower-haunting Beetles, and even the mandibles are flexible
and hairy in the Scarabocus- beetles. Fritz Miiller has found a
singular resemblance to the proboscis of a Moth in a species of
Nemognatha, where the maxilloc are transformed into two sharp
grooved bristles 12 mm. long, which, when opposed, form a
tube, but are incapable of rolling up.*

In the Honey Bee (fig. 23) nearly all the mouth-parts of the
Cockroach are to be made out, though some are small and others
extremely produced in length. The mandibles (Mn) are not
much altered, and are still used for biting, as well as for knead-
ing wax and other domestic work. The mandibular teeth have
proved inconvenient, and are gone. The lacinia of the maxilla
(Mxl) forms a broad and flexible blade, used for piercing succu-
lent tissues, but the galea has disappeared, and there is only a
vestige of the maxillary palp (J/lr/j). In the second pair of
maxillae the palp (Lp) is prominent; its base forms a blade,
while the tip is still useful as an organ of touch. The para-
glossse (P(() can be made out, but the Iacinia3 are fused to form
the long, hairy tongue. This ends in a spoon-shaped lobe (not
unlike the "finger" of an elephant's trunk), which is used both
for licking and for sucking honey.

The proboscis of the Bee is therefore more like a case of
instruments than a single organ. The mandibles form a strong

O O o

pair of blunt scissors. The maxillae are used for piercing, for
stiffening and protecting the base of the tongue, and when

* Ein Klifer mit Schmetterlingsriissel, Kosmos, Bd. VI. We take this reference
from Hermann Muller's Fertilisation of Flowers.

ITS OUTER SKELETON.

closed they form an imperfect tube outside, the tongue, which,
according to Hermann Miiller, is probably suctorial. The labial
palps are protective and sensory. Lastly, the central part, or
tongue, is a split tube used for suction ; it is very long, so as to

Fig. 23. — Mouth-parts of Honey Bee.

Fig. 23 A. —Diagram of Mouth-parts of Honey Bee.

THE COCKROACH I

penetrate deep flower-cups, and hairy, so that pollen may stick
to it. When the proboscis is not in use it can be slid into the
men turn (M), while it and the mentum together can be drawn
out of the way downwards and backwards.*

In the singular suctorial mouth of Moths and Butterflies we
observe, first of all, the great development of the maxillae.

Fig. 24.— Mouth-parts of Burnet Moth.

Fig. 24 A. — Diagram of Mouth-parts
of Moth.

Each forms a half-tube, which can be accurately applied to its
fellow, so as to form an efficient siphon. In many species the
two halves can be held together by a multitude of minute
hooks.f At the base of each maxilla is a rudimentary palp
(Mxp). The mandibles (Mn) are also rudimentary and perfectly
useless. The labium, which was so important to the larva as a
spinneret, has disappeared almost completely, but the labial
palps (Lp) are large and evidently important.

* An interesting account of the structure and mode of action of the Bee's tongue
is to be found in Hermann Miiller's Fertilisation of Flowers, where also the evolu-
tion of the parts is traced through a series of graduated types.

t See Newport's figure of Vanessa atalanta (Todd's Cyc. , Art. Insecta), or Burgess
on the Anatomy of the Milk-weed Butterfly, in Anniversary Mem. of Boston Soc.
Nat. Hist., pi. ii., figs. 8-10 (1880).

ITS OUTER SKELETOX.

In Diptera both piercing and sucking parts are usually
present. The Gad-fly (fig. 25) is typical. Here we recognise
the labrum (Lbr), mandible (Mti), and maxilla (Mxl) of the
Cockroach transformed into stylets. The maxillary palp (Mxp)
is still sensory. A pointed process, stiffened by chitinous ribs,
is developed from the back of the labrum. This is the

LIBRA

"Fig. 25. — Mouth-parts of Gad-fly
(Tabanus).

Fig. 25 A. — Diagram of Mouth-parts
of Gad-fly.

epipharynx (Ep), a process undeveloped in the Cockroach,
though conspicuous in some Coleoptera. All these parts are
overtopped by the suctorial labium (Lm), which has a two-
lobed expansion at the end. In the more specialised Diptera
this becomes a kind of cupping-glass. The Gad-fly is inter-
mediate between the Gnat, in which all the mouth-parts are
converted into piercing organs of extraordinary length and
sharpness, and such flies as the House-fly and Blow-fly, where
the sucking labium forms an organ of the most elaborate kind,
the piercing organs undergoing a marked reduction. Except
where the labium is short, it is doubly or trebly hinged, so that
it can be readily tucked away under the chin.

THE COCKROACH :

In Hemiptera the long- four-jointed labium (Lm) forms a
sheath for the stylets. When not in use the whole apparatus
is drawn up beneath the head and prothorax. The mandibles
(IMii) are sharp at the tip, and close like a pair of forceps, en-
closing the maxillae (lAr). These are of unequal length, only
one reaching the end of the mandibular case. Both have saw
teeth on the free edge. Palps are entirely wanting.

Lbr

Fig. 26. — Mouth-parts of Bug. Copied from
Landois, Zeits. f. wiss. Zool., Bd. XVIII. ,
taf. xi., fig. 3.

Fig. 26A. — Diagram of Mouth-parts
of Bug.

Comparing the four kinds of suctorial mouths, of which the
Bee, the Moth, the Fly, and the Bug furnish examples, we
observe that the sucking-tube is formed in the Moth out of the
two maxillae, in the other three out of the labium. Of these
last the Bee has the edges of the labium turned down, so that
the siphon becomes ventral ; in the Bug and Fly the edges

ITS OUTER SKELETON. 55

are turned up, and the siphon becomes dorsal. The more
specialised flies have the simple arrangement of the Bug com-
plicated by a s\Tstem of branching tubes, which are probably a
special modification of the salivary duct. Similar as the
mouth-parts of the four types may be in regard to their mode
of working, they cannot be reduced to any common plan which
differs materially from that presented by the jaws of the
Cockroach.

Composition of Head.

In all Insects fusion of the primitive elements of the head
begins so early and is carried so far, that it is extremely difficult
to discover the precise way in which they are fitted together.
The following facts have been ascertained respecting the develop-
ment of the parts in question. At a very early stage of
embryonic life the body of the Insect becomes divided into a
series of segments, which are at fewest fourteen (in some
Diptera), while they are not known to exceed seventeen.* Each
segment is normally provided with a pair of appendages. The
foremost segment soon enlarges beyond the rest, and becomes
divided by a median groove into two " procephalic lobes. "f Of
the appendages the first eight pairs are usually more prominent
than the rest, and of different form ; those of the eighth
segment, which may be altogether inconspicuous, never attain
any functional importance. The first four pairs of appendages
are budded oif from the future head, while the next three pairs
form the walking legs, and are carried upon the thoracic segments.
All the existing appendages of the fore part of the body are
thus accounted for, but the exact mode of formation of the head
has not yet been made out. The chief part of its walls, includ-
ing the clypeus, the compound eyes, and the epicranial plates,
arise from the procephalic lobes, and represent the much altered
segment of which the antennae are the appendages. The labrum
is a secondary outgrowth from this segment, and, in some cases
at least, it originates as a pair of processes wrhich resemble true

* Balfour, Embryology, Vol. I., p. 337.

t Huxley, Med. Times and Gazette, 1856-7; Linn. Trans., Vol. XXII. , p. 221,
and pi. 38 (1858).

56 THE COCKROACH :

appendages, though it is unlikely that such is their real
character. No means at present exist for identifying the terga
and sterna of the head, nor have the gena, the occipital frame,
and the cervical sclerites (described below) been assigned to
their segments.* It is worthy of notice that in the stalk-eyed
Crustacea, the head, or what corresponds to the head of Insecta,
consists of either five or six somites, taking into account a
diversity of opinion with respect to the eyestalks, while only
four pairs of appendages can be certainly traced in the head of
the Insect. The mandibles and maxilla) exist to the same
number in both groups, and are homologous organs, so far as is
known ; the numerical difference relates therefore to the antennae,
of which the Crustacean possesses two pairs, the Insect only
one. Whether the pair deficient in the Insect is altogether
undeveloped, or represented by the pair of prominences which
give rise to the labrum,f is a question of much theoretical
interest and of not a little difficulty.

The following table shows the appendages of the head and
thorax in the two classes. The homologies indicated are, how-
ever, by no means established. J

CRAYFISH. COCKROACH.

Antennae.

Eyestalks.

Antennules.
Antennae.

Mandibles.
Maxilla? (1).
Maxillae (2).

Maxillipeds (1).

Maxillipeds (2).
Maxillipeds (3).

Mandibles.
Maxilla* (1).
Maxillae (2).

Thoracic Legs (1).
Thoracic Legs (2).
Thoracic Legs (3).

* "I think it is probable that these cervical sclerites represent the hinclermost of
the cephalic somites, while the band with which the maxilla? are united, and the
genre, are all that is left of the sides and roof of the first maxillary and the mandi-
bular somites. "--Huxley, Anat. Invert. Animals, p. 403.

t Balfour, Embryology, Vol. I., note to p. 337.

I J. S. Kingsley in Q. J. Micr. Sci. (1885), has reviewed the homology of Insect,
Arachnid, and Crustacean appendages, and comes to conclusions very different from

ITS OUTER SKELETON. 57

Neck.

The neck is a narrow cylindrical tube, with a flexible wall
strengthened by eight plates, the cervical sclerites, two of which
are dorsal, two ventral, and four lateral. The dorsal sclerites
lie immediately behind the head (fig. 14) ; they are triangular,
and closely approximated to the middle line. The inferior
plates (fig. 27) resemble segments of chitinous hoops set trans-
versely, one behind the other, rather behind the dorsal sclerites,
and close behind the submentum. There are two lateral
scierites on each side of the neck (fig. 27), a lower squarish
one, which is set diagonally, nearly meeting its fellow across
the ventral surface, and an oblong piece, closely adherent to
the other, which extends forwards and upwards towards the
dorsal side.

Thorax.

The elements of the thoracic exoskeleton are simpler in the
Cockroach than in Insects of powerful flight, where adaptive
changes greatly obscure the primitive arrangement. There are
three segments, each defended by a dorsal plate (terguni) and a
ventral plate (sternum}. The sterna are often divided into
lateral halves. Of the three terga the first (pronotum) is the
largest ; it has a wide free edge on each side, projects forwards
over the neck, and when the head is retracted, covers this also,
its semi-circular fore-edge then forming the apparent head-end
of the animal. The two succeeding terga are of nearly equal
size, and each is much shorter than the pronotum, contrary to
the rule in winged Insects.*

those hitherto accepted. He classifies the appendages as pre-oral (Insect-antenn?e)
and post-oral, and makes the following comparisons :—

HEXAPODA. ACERATA.

( = Insecta + Myriopoda ?)

(1) Antennae.

(2) Mandibles.

(3) Maxilla.

(4) Labium.

(5) 1st pair legs.

(6) 2nd pair legs.

(=Arachnida + Limulus.)

Absent.
Chelicerse.
Pedipalpi.
1st pair legs.
2nd pair legs.
3rd pair legs.

CRUSTACEA.

Absent.
Antennules.
Antennae.
Mandibles.
1st Maxillae.
2nd Maxillae.
1st Maxillipeds.

(7) 3rd pair legs. 4th pair legs.

Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antenna; are post-
oral in Apus, and probably in all other Crustacea.

* Many Orthoptera, which seize their prey with the fore legs, have a veiy long
pronotum.

THE COCKROACH I

All the terga are dense and opaque in the female ; in the
male the middle one (mesonatmri) and the hindmost (mctano-
tum) are thin and semi-transparent, being ordinarily overlaid
by the wing-covers. While the thoracic terga diminish back-
wards, the sterna increase in extent and firmness, proportionally
to the size of the attached legs. The prosternum is small and
coffin-shaped ; the mesosternum partly divided into lateral
halves in the male, and completely so in the female. The
metasternum is completely divided in both sexes, while a
median piece, carrying the post-fiirca, intervenes between its
lateral halves in the male. Behind the sterna, especially in the

Fig. 27. — Ventral Plates of Neck and Thorax of Male Cockroach.
I, prosternum ; II, mesosternum ; III, metasternum. X 6.

case of the second and third, the flexible under-surface of the
thorax is inclined, so as to form a nearly vertical step. In the
two hinder of these steps a chitinous prop is fixed ; each is
Y-shaped, with long, curved arms for muscular attachment, and
a central notch, which supports the nerve-cord. The hind-
most of these, known as the post-furca, lies immediately behind

ITS OUTER SKELETON. 59

the metasternum, and its short basal piece is attached between
the lateral halves of that plate. Behind the mesosternum is a
somewhat slighter prop, the medi-furea. A third piece of similar
nature (the ante-furca), which is well developed in some Insects —
e.g., in Ants — is apparently wanting in the Cockroach, though
there is a transverse oval plate behind the prosternum, which*
may be a rudimentary furca.

Fig. 27 shows two conical processes which lie in the middle
line of the ventral surface of the thorax, one in front of the
metasternum, the other in front of the mesosternum. These
are the thoracic pits, tubular apodemata, serving for the
insertion of muscles. The occurrence of stink-glands in
the thorax of Hemiptera,* and of so-called poison-glands
in the thorax of Solpuga, led us to look for glands in
connection with these processes, but we have found none.

Thoracic Appendages. Legs; Wings.

Three pairs of legs are attached to the thoracic segments ;
they regularly increase in size from the first to the third, but
hardly differ except in size ; the peculiar modifications which
affect the fore pair in predatory and burrowing Orthoptera
(Mantis, Gryllotalpa), and the third pair in leaping Orthoptera
(Grasshoppers, &c.), being absent in the cursorial Blattina. Each
leg is divided into the five segments usual in Insects (see fig. 28).
The coxa is broad and flattened. The trochanter is a small piece
obliquely and almost immovably attached to the proximal end
of the femur, on its inner side. The femur is nearly straight
and narrowed at both ends ; along its inner border, in the
position occupied by the stridulating apparatus of the hind leg
of the Grasshoppers, is a shallow longitudinal groove, fringed
by stiff bristles. The tibia is shorter than the femur in the fore
leg, of nearly the same length in the middle leg, and longer in
the hind leg ; it is armed with numerous stiff spines directed
towards the free end of the limb. There are usually reckoned
five joints in the tarsus, which regularly diminish in length,
except that the last joint is as long as the second. All the

* Also in Phasmidce (see Scudder, Psyche, Vol. I., p. 137).

THE COCKROACH

Fig. 28. — The three Thoracic Legs of a Female Cockroach. I, s, sternum ; ex, coxa ;
tr, trochanter ; fe, femur ; tb, tibia ; ta, tarsus. In IllA the coxa is
abducted, and the joints a (episternum) and b slightly separated. X 4.

ITS OUTER SKELETON. 61

joints bear numerous fine but stiff hairs upon the walking
surface. The extremity of the fifth joint is segmented off, and
carries a pair of equal and strongly curved claws,*

At the base of each leg are several chitinous plates (fig. 28),
upon which no small labour has been bestowed by different
anatomists. They are arranged so as to form two joints inter-
mediate between the coxa and the sternum, and these two joints
admit of a hinge-like movement upon each other, while their
other ends are firmly attached to the coxa and sternum respec-
tively. (Compare III and IIL\, fig. 28.) These parts in the
Cockroach may be taken for two basal leg-joints which have
become adherent to the thorax. In other cases, however, they
plainly belong to the thorax, and not to the leg. In the Mole-
cricket, for instance, similar plates occur ; but here they are
firmly united, and form the lateral wall of the thorax. In the

Locust they become vertical, and lie one in front of the other.
Most authors have looked upon them as regular elements of a
typical somite. They regard such a segment as including two
pleural elements — viz., a dorsal plate (epimeron), and a ventral
plate (episternum). We have already (p. 34) given reasons for
doubting the constancy of the pieces so named. It is not
inconvenient, however, to denote by the term episternum the
joint which abuts upon the sternum ; for the joint which is
applied to the coxa no convenient term exists, and its occurrence
in Insects is so partial, that the want need not be supplied at
present.f Both joints are incompletely subdivided. In the first
thoracic segment of the Cockroach they are less firmly con-
nected than in the other two.

Cockroaches of both sexes are provided with wings, which,,
however, are only functional in the male. The wing-covers (or
anterior pair of wings) of the male are carried by the second
thoracic segment. As in most Orthoptera genuina, they are
denser than the hind wings, and protect them when at rest.
They reach to the fifth segment of the abdomen, and one

* Professor Huxley (Anat. Invert. Animals, p. 404) points out that the so-called
pulviUus ought to be counted as a sixth joint. The same is true of the foot of
Diptera and Hymenoptera, where there are six tarsal joints, the last carrying the
claws. (Tuff en West on the Foot of the Fly. Linn. Trans., Vol. XXIII.)

t The nomenclature adopted by Packard (Third Report of U.S. Entomological
Commission) seems to us open to theoretical objections.

THE COCKROACH

wing-cover overlaps the other. Branching veins or nervures
form a characteristic pattern upon the surface (figs. 4, 29), and
it is mainly by means of this pattern that many of the fossil
species are identified and distinguished. The true or posterior
wings are attached to the metathorax. They are membranous
and flexible, but the fore-edge is stiffened, like that of the wing-
covers, by additional chitinous deposit. When extended, each
wing forms an irregular quadrant of a circle ; when at rest, the
radiating furrows of the hinder part close up fan-wise, and the
inner half is folded beneath the outer.* The wing reaches back
as far as the hinder end of the fourth abdominal segment. The
wing-covers of the female are small, and though movable, seem
never to be voluntarily extended ; each covers about one-third
of the width of the mesonotum, and extends backwards to the

Fig. 29. — Wings and Wing-covers of Male Cockroach. X 4.

middle of the metanotum. A reticulated pattern on the outer
fourth of the metanotum plainly represents the hind wing ; it
is clearly rather a degeneration or survival than an anticipation
of an organ tending towards useful completeness.

* On wing-plaiting and wing-folding in Blattarue see Saussure, Etudes sur 1'aile
des Orthopteres. Ann. Sci. Nat., Ser. 5° (Zool.), Tom. X.

ITS OUTER SKELETON. 63

The rudimentary wing of the female Cockroach illustrates
the homologv of the wings of Insects with the free edges of

C-J •/ t*

thoracic terga, and this correspondence is enforced by the study
of the development of the more complete wings and wing-covers
of the male. The hinder edges of the terga become produced
at the later moults preceding the completely winged stage, and
may even assume something of the shape and pattern of true
wings ; it is not, however, true, though more than once stated,
that winged nymphs are common. Adults with imperfectly
developed wings have been mistaken for such.

Origin of Insect Wings.

The structure of the wing testifies to its origin as a fold of
the chitinous integument. It is a double lamina, which often
encloses a visible space at its base. The nervures, with their
vessels and tracheal tubes, lie between the two layers, which,
except at the base, are in close contact. Oken termed the wings
of an Insect " aerial gills," and this rather fanciful designation
is in some degree justified by their resemblance to the tracheal
gills of such aquatic larvae as those of Ephemeridce, Perlidac,
Phryganidoc, &c. In the larva of Cldoeon (Ephemera) dipterum
(fig. 30), for example, the second thoracic segment carries a pair
of large expansions, which ultimately are replaced by organs
of aerial flight. The abdominal segments carry similarly
placed respiratory leaflets, the tracheal gills, which by their
vigorous flapping movements bring a rush of water against
their membranous and tracheated surfaces.

Gegenbaur* has argued from the resemblance of these
appendages to wings, that the wing and the tracheal leaflet are
homologous parts, and this view has been accepted as probable
by so competent an observer as Sir John Lubbock.'f'

The leaflets placed most advantageously for propulsion seem
to have become exclusively adapted to that end, while the
abdominal gills have retained their respiratory character. At
the time of change from aquatic to terrestrial life, which takes
place in many common Insects when the adult condition is

* Gruudziige der Yergl. Anat. (Arthropoden, Athnmugsorgane. )
f Origin and Metamorphoses of Insects, p. 73.

TIIK COCKROACH

Fig. 30. Chloeon (Chloeopsis) dipterum. Larva in eighth stage, with wings
and respiratory leaflets. X 14. Copied from Vayssiere (loc. cit. ).

ITS OUTER SKELETON. 65

assumed, and which, according to Gegenbaur, was a normal
event among primitive Insects, the trachea! gill is supposed to
disappear, and in its place, at the next moult, an opening, the
stigma, is formed by the rupture of an air-tube. Gegenbaur
supposes that the primitive Insects were aquatic, and their
tracheal system closed. The tracheal gill he takes to be the
common structure which has yielded organs so unlike as the
wing and the stigma.

The zoological rank of the Insects (Ephemeridae, Perlidae,
and Libellulidse), in which tracheal gills are most usual, is not
unfavourable to such an explanation. Lubbock has given
reasons for regarding Campodea and the Collembola (of the
order Thysanura) as surviving and not very much altered
representatives of the most primitive Insects, and he has shown
that no great amount of modification would be required to
convert the terrestrial Cnmpodea into the aquatic Chloeon-
nymph.* We must not forget, however, that tracheal gills
are by no means restricted to these families of low grade.
Trichoptera, a few Diptera, two Lepidoptera (Nymphula and
Acentropus), and two Coleoptera (Gyrinus and Elmis),^ have
tracheal gills, and a closed tracheal system in the larval condi-
tion. We cannot suppose that these larvae of higher orders
represent an unbroken succession of aquatic forms, but if we
refuse to adopt this alternative, we must admit that the closed
tracheal system with tracheal gills may be an adaptive modifi-
cation of the open system with stigmata.

It is well known J that in certain Ephemeridoo (e.g., Tricorythus
and Ccenis) a pair of anterior tracheal gills may become trans-
formed into large plates, which partly protect the gills behind
(fig. 31). A similar modification of the second and third
thoracic gills in Prosopistoma and B&tisca brings all the
functional respiratory organs under cover, and these enlarged
plates resemble stiff and simple wings very closely.

* Palmen cites one striking proof of the low position of Ephemeridce among
Insects. Their reproductive outlets are paired and separate, as in Worms and
Crustacea.

f These examples are cited by Palmen.

% Eaton, Trans. Ent. Soc., 1868, p. 281; Vayssiere, Ann. Sci. Nat., Zool., 1882,
p. 91.

THE COCKROACH :

Fig. 31. — Tricorythus. Adult larva, with three functional leaflets. The next
leaflet in front is converted into a protective plate. X 7.

A, protective plate of Tricorythus larva, seen from the outside. X 26.

B, the same from within, showing the attached respiratory appendage.

C, protective plate of Coenis larva, without respiratory appendage.

All the figures are copied from Vayssiere.

ITS OUTER SKELETON. 67

Palmen* has subjected Gregenbaur's hypothesis to a very
searching examination. He observes that: —

1. In Campodea, and presumably in other primitive Insects,
the tracheal system is not closed and adapted for aquatic
respiration, but open. Tracheal gills are not by any means
confined to the lowest Insects. (See above, p. 65.)

2. Tracheal gills are not always homodynamous or morpho-
logically equivalent. In Ephemeridfe, some are dorsal in
position, some ventral (first abdominal pair in Oligoneuria and
Rhithrogena} ; they may be cephalic, springing from the base of
the maxilla, as in Oligoneuria and Jolia ; Jolia has a branchial
tuft at the insertion of each of the fore legs.-f* In Perlids-e the
tracheal gills may have a tergal, pleura), sternal, or anal
insertion. In some Libellulidae also, anal leaflets occur.}

3. Tracheal gills never perfect^ agree in position and
number with the stigmata throughout the body. Sometimes
they occur on different rings, sometimes on different parts of
the same ring. Gegenbaur's statements on this point are
incorrect.

4. Tracheal gills may co-exist with stigmata. In Perlidae
the tracheal gills persist in the imago, and may be found, dry
and functionless, beneath the stigmata. In Trichoptera they
gradually abort at successive moults, and in some cases remain
after the stigmata have opened.

5. Stigmata do not form by the breaking off of tracheal
appendages, but by the enlargement of rudimentary tracheal

* Zur Morphologic des Tracheensystems (1877).

f We take these instances from Eaton, Monograph of Ephemeridse, Linn. Trans.,
1883, p. 15.

£ Charles Brougniart has lately described a fossil Insect from the Coal Measures of
Commentry, which he names Corydaloides Scudderi, and refers to the Pseudo-
Neuroptera. In this Insect every ring of the abdomen carries laminae, upon which
the ramified tracheae can still be made out by the naked eye. Stigmata co-existed
with these tracheal gills. (Bull. Soc. Sci. Nat. de Rouen, 1885.)

Some Crustacea are furnished with respiratory leaflets, curiously like those of
Tracheates, with which, however, they have no genetic connection. In Isopod
Crustacea the exopodites of the anterior abdominal segments often form opercula,
which protect the succeeding limbs. In the terrestrial Isopods, Porcellio and
Armadillo, these opercula contain ramified air-tubes, which open externally, and
much resemble tracheae. The anterior abdominal appendages of Tylus are provided
with air-chambers, each lodging brush-like bundles of air-tubes, which open to the
outer air. Lamellae, projecting inwards from the sides of the abdominal segments,
incompletely cover in the hinder part of the ventral surface of the abdomen, and
protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacea, "Vol. III.)

68 THE COCKROACH :

branches, which open into the main longitudinal trunks. In
larvae with aquatic respiration these branches exist, though they
are not functional.

Palmen's objections must be satisfactorily disposed of before
Gegenbaur's explanation, interesting as it is, can be fully
accepted. Palmen has proved, what is on other grounds clear
enough, that stigmata are more ancient than trachea! gills,
aerial tracheate respiration than aquatic. But there is nothing
as yet to contradict the view that the first Insect-wings were
adapted for propulsion in water, and that they were respiratory
organs before they became motor. It is Gegenbaur's explana-
tion of the origin of stigmata, and not his explanation of the
origin of wings, which is refuted by Palmen.

Abdomen.

In the abdomen of the female Cockroach eight terga (1-7 ;
10) are externally visible. Two more (8, 9) are readily dis-
played by extending the abdomen ; they are ordinarily
concealed beneath the seventh tergum. The tenth tergum is
notched in the middle of its posterior margin. A pair of
triangular " podical plates," which lie on either side of the
anus, and towards the dorsal surface, have been provisionally
regarded by Prof. Huxley as the terga of an eleventh segment.
Seven abdominal sterna (1-7) are externally visible. The first
is quite rudimentary, and consists of a transversely oval plate ;
the second is irregular and imperfectly chitinised in front ; the
seventh is large, and its hinder part, which is boat- shaped, is
divided into lateral halves, for facilitating the discharge of the
large egg-capsule.

In the male Cockroach ten abdominal terga are visible
without dissection (fig. 33, p. 70), though the eighth and
ninth are greatly overlapped by the seventh. The tenth
tergum is hardly notched. Nine abdominal sterna are readily
made out, the first being rudimentary, as in the female. The
eighth is narrower than the seventh, the ninth still narrower,
and largely concealed by the eighth ; its covered anterior part
is thin and transparent, the exposed part denser. This forms
the extreme end of the body, except that the small sub-anal styles
project beyond it. The podical plates resemble those of the
female.

ITS OUTER SKELETON.

Pleural elements are developed in the form of narrow
stigmatic plates, with the free edge directed backwards. These
lie between the terga and sterna, and defend the spiracle.*

The modifications of the hindmost abdominal segments will
be more fully considered in connection with the reproductive
organs.

<f 9

Fig. 32. — Under side of Abdomen of Male and Female Cockroach. X 4.

The high number of abdominal segments found in the Cock-
roach (ten or eleven) is characteristic of the lower orders of
Insecta. It is never exceeded ; though in the more specialised
orders, such as Lepidoptera and Diptera, it may be reduced to
nine, eight, or even seven. The sessile abdomen of the Cock-
roach is primitive with respect to the pedunculate abdomen
found in such insects as Hymenoptera, where the constricted
and flexible waist stands in obvious relation to the operations
of stinging and boring, or to peculiar modes of oviposition.
The first abdominal segment, which is especially liable to dis-
location and alteration in Insects, occupies its theoretical
position in the Cockroach, though both tergum and sternum

* Gerstaecker has found in the two first abdominal segments of Corydia carunculi-
gera (Blattarice) pleural appendages, which are hollow and capable of protrusion.
They have no relation to the stigmata, which are present in the same segments, and
their function is quite unknown. See Arch. f. Naturg., 1861, p. 107.

THE COCKROACH I

are reduced in size. The sternum is often altogether wanting,
while the tergum may unite with the metathorax.

The externally visible appendages of the abdomen are the
cerci and the st}des of the male Cockroach. The cerci are found
in both sexes ; they are composed of sixteen rings each, and
project beneath the edge of the tenth tergum. They are
capable of erection by special muscles, and are supplied by large
nerves.* The sub-anal styles are peculiar in their insertion,
being carried upon the sternum of their segment (the ninth).

Fig. 33. — Profile of Male and Female Cockroach. X 4.

The abdominal segments are never furnished with functional
legs in adult Insects, but representatives of the lost appendages
are often met with in larvae. According to Butschli,f all the
abdominal segments are provided with appendages in the
embryo of the Bee, though they disappear completely before
hatching. Some Hymenopterous larvae have as many as eight
pairs of abdominal appendages, Lepidopterous larvae at most
five (3-6; 10)4

* Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera) ;
in the Earwig they become modified and form the forceps. The "caudal filaments"
of Apus are curiously like cerci.

The cerci are concealed in the American Cryptocercus, Scudd. (Fam. Panesthidce).

t Entw. der Biene. Zeits. f . wiss. Zool. l>d. XX. Or, see Balfour's Embryology,
Vol. L, p. 338.

% From more recent observations it is probable that abdominal appendages are
usually present in the embryos of Orthoptera, Coleoptera, Lepidoptera, and possibly
Hymenoptera. The subject is rapidly advancing, and more will be known very
shortly.

CHAPTER V.

THE MUSCLES; THE FAT-BODY AND CCELOM.

SPECIAL REFERENCES.

VIALLANES. Histologie et Developpement des Insectes. Aun. Sci. Nat., Zool.,
Tom. XIV. (1882).

KUHNE in Strieker's Histology, Vol. I. , chap. v.

PLATEAU. Various Memoirs in Bull. Acad. Roy. de Belgique (1805, 1866, 1883,
1884). [Relative and Absolute Muscular Fo7~ce.]

LEYDIG. Zum feineren Bau der Artliropoden. Miiller's Archiv., 1855.

WEISMANN. Ueber zwei Typen contractilen Gewebes, &c. Zeits. fur ration.
Medicin. Bd. XV. (1862).

Structure of Insect Muscles.

THE muscles of the Cockroach, when quite fresh, appear
semi-transparent and colourless. If subjected to pressure or
strain they are found to be extremely tender. Alcohol hardens
and contracts them, while it renders them opaque and brittle.

The minute structure of the voluntary or striped muscular
fibres of Vertebrates is described in common text-books.* Each
fibre is invested by a transparent elastic sheath, the sarcolemma,
and the space within the sarcolemma is subdivided by trans-
verse membranes into a series of compartments. The com-
partments are nearly filled by as many contractile discs,
broad, doubly refractive plates, which are further divisible
into prismatic columns, the sarcous elements, each being as
long as the contractile disc. Successive sarcous elements,
continued from one compartment to another, form the
primitive fibrils of the muscle. In cross-section the fibrils
appear as polygonal areas bounded by bright lines. Outside
the fibres, but within the sarcolemma, are nuclei, imbedded in
the protoplasm, or living and formative element of the tissue.

* See, for example, Klein's Elements of Histology, chap. ix.

72 THE COCKROACH :

The muscular fibres of Insects present some important
differences from the fibres just described. The nuclei are often
found in the centre, and not on the surface of the fibres in both
Insects and Crustacea. In both classes the fibrils are frequently
subdivided into longitudinal strands, which have not been
distinguished in Vertebrate muscles (Viallanes). The sarco-
lemma is often undeveloped. Lastly, Insects, like other
Arthropoda, exhibit the remarkable peculiarity that not only
their voluntary muscles, but all, or nearly all, the muscles of
the body, even those of the digestive tube, are striated.*

General Arrangement of Insect Muscles.

The arrangement of the muscles in an Insect varies greatly
according to situation and mode of action. Some of the
abdominal muscles consist solely of straight parallel bundles,
while the muscles of the limbs usually converge to tendinous
insertions. In certain larvae, where the segments show hardly
any differentiation, the muscles form a sheet which covers the
whole body, and is regularly segmented in correspondence with
the exo-skeleton. As the movements of the body and limbs
become more varied and more energetic, the muscles become
grouped in a more complicated fashion, and the legs and wings
of a flying Insect may be set in motion by a muscular apparatus
almost as elaborate as that of a bird.

Muscles of the Cockroach.

The following: short notes on the muscles of the Cockroach,

~ '

aided by reference to the figures, will render the more note-
worthy features intelligible. A very lengthy description, far
beyond our space or the reader's patience, would be required to
explain in detail the musculature of the head, limbs, and other
specialised regions.

STERNAL MUSCLES OF ABDOMEN. — The longitudinal sternal
musc/es (fig. 34) form a nearly continuous transversely seg-

* The exceptions relate chiefly to the alary muscles of the pericardial septum.
Lowne (Blow-fly, p. 5, and pi. v. ) states that some of the thoracic muscles of that
Insect are not striated.

THE MUSCLES ; THE FAT-BODY AND CCELOM.

mented sheet, covering the ventral surface between the fore-
edge of the second abdominal sternum and the fore-edge of the
seventh. These muscles, in conjunction with the longitudinal
tergal muscles, tend to telescope the segments.

Head muscles-

Add, of coxa

Abd. of coxa --A-

Ext. fern. ...
1st tergo-st.

Long, stern.

Obi. sternal

Tergo-stern.

Fig. 34. — Muscles of Ventral Wall, with the Nerve-cord. X 5.

THE COCKROACH :

Head muscles-

Long, tergal

Obi. tergal

Alary tendon

Tergo-stern.

Fig. 35. — Muscles of Dorsal Wall, with the Heart and Pericardial Tendons. X 5.

THE MUSCLES ; THE FAT-BODY AND CCELOM. 75

The oblique sternal muscles (fig. 34), which are very short,
connect the adjacent edges of the sterna (2-3, 3-4, 4-5, 5-6,
6-7). They extend inwards nearly to the middle line, but, like
the longitudinal sternal muscles, they are not developed beneath
the nerve-cord. Acting together, the oblique sternal muscles
would antagonise the longitudinal, but it is probable that they
are chiefly used to effect lateral flexion of the abdomen, and
that only the muscles of one side of the abdomen contract at
once.

The tergo-sternal (or expiratory) muscles (figs. 35 and 36)
form vertical pairs passing from the outer part of each abdo-
minal sternum to the corresponding tergum. Their action is to
approximate the dorsal and ventral walls, and thus to reduce
the capacity of the abdomen. The first tergo-sternal muscle
has its ventral insertion into the stem of the postfurca, and
takes an oblique course to the first abdominal tergum.

TERGAL MUSCLES OF ABDOMEN. — The longitudinal tergal
muscles extend from the fore part of each abdominal tergum,
including the first, to the same part of the tergum next behind.
They are interrupted by longitudinal spaces, so that the
muscular sheet is less continuous than on the ventral surface,
and has a fenestrated appearance. The direction of the fibres
is slightly oblique.

Oblique tergal muscles, resembling the oblique muscles of the
sterna, are also present.

In the thorax the general arrangement of the muscles is
greatly modified by the altered form of the dorsal and ventral
plates, and by the attachment of powerful limbs.

STERNAL MUSCLES OF THORAX. — Two tubular apodemes,
lying one behind the other, project into the thorax from the
ventral surface (p. 59 and fig. 27). To the foremost of these
are attached three paired muscles and one median muscle.
The median muscle passes to the second tubular apodeme. The
anterior pair pass forwards and outwards to the base of the
prothoracic leg ; the next pair directly outwards to the base of
the middle leg ; while the posterior pair pass outwards and
backwards to the arms of the medifurca. From the second
tubular apodeme, in front of the metasternum, four pairs of
muscles spring. Those of the anterior pass forwards and out-

THE COCKROACH :

wards to the coxa, of the fore limb ; the second pair directly
outwards to the base of the metathoracic legs ; the third pair
backwards and outwards to the arras of the postfurca ; the
fourth pair backwards to the second abdominal sternum.

Add. of coxa

Ext. fern. ... '

Abd. of coxa

Tergo-st.

Fig. 36. — Muscles of lateral wall, &c. X 5.

The muscles attached to the medi- and postfurca (other than
those connecting them with the tubular apodemes) are : —

THE MUSCLES ; THE FAT-BODY AND CCELOM.

— Add. of coxa

. Abd. of coxa

Ext. fern.

-- Fl. fern.

FL tib.

Ext. tib.

_ _ » _. Fl. tars.

Retr. tars.

Fig. 37. — Muscles of left mesothoracic leg, seen from behind. The muscles are-
Adductor and abductor of the coxa ; extensor and flexor of femoral joint ; flexor
and extensor of tibial joint; flexor of tarsus; and a retractor tarsi, which swings
the tarsus backwards, so that it points away from the head. It is opposed by
another muscle, which moves the tarsus forwards. Both muscles parallelise the
tarsus to the axis of the body, but in opposite directions.

78 THE COCKROACH :

(1) A pair passing from the posterior edge of the arms
of the medifurca to the stem of the postfurca ; (2) a pair
which diverge from the stem of the postfurca and proceed to
the fore part of the second abdominal sternum ; (3) a pair
passing from the posterior edge of the arms of the postfurca,
these are directed inwards and backwards, and are inserted into
the hinder part of the second abdominal sternum ; (4) a pair
already mentioned, which correspond in position and action to
the tergo-sternal muscles, and spring from the stem of the post-
furca, passing upwards and outwards to the sides of the first
abdominal tergum.

The muscles attached to the arms of each furca pass to other
structures in or near the middle line of the body. The pull of
such muscles must alter the slope of the two steps in the
ventral floor of the thorax (p. 58, and fig. 3, p. 12). When the
furca is drawn forwards, the step is rendered vertical or even
inclined forward, the sterna being approximated ; while, on the
other hand, a backward pull brings the step into a horizontal
position, and separates the sterna.

TERGAL MUSCLES OF THORAX. — The longitudinal tergal muscles
are much reduced in width when compared with those of the
abdomen. Sets of obliquely placed muscles, which may be
called the lateral thoracic muscles, arise from near the middle of
each tergum, and converge to tendinous insertions on the fore
edge of each succeeding tergum, close to the lateral wall of the
body.

The principal muscles of the legs are figured and named, and
their action can readily be inferred from the names assigned to
them.

Insect Mechanics.

The mechanics of Insect movements require exposition and
illustration far beyond what is possible in a book like this.
Even the elaborate dissections of Lyonnet and Straus-Durckheim
are not a sufficient basis for a thorough treatment of the sub-
ject, and until we possess many careful dissections, made by
anatomists who are bent upon mastering the action of the parts,
our views must needs be vague and of doubtful value. Zoologists

THE MUSCLES ; THE FAT-BODY AND CCELOM. 79

of great eminence have been led into erroneous statements when
they have attempted to characterise shortly a complex animal
mechanism which they did not think it worth while to analyse
completely.*

The action of flight and the muscles attached to the wings
are best studied in Insects of powerful flight. The female
Cockroach cannot fly at all, and the male is by no means a good
flier. Both sexes are, however, admirably fitted for running.

In running, two sets, each consisting of three legs, move
simultaneouslv. A set includes a fore and hind limb of the

•J

same side and the opposite middle leg. Numbering them from
before backwards, and distinguishing the right and left sides by
their initial letters, we can represent the legs which work
toether as —

Lo Re

L! R%2 LS

The different legs have different modes of action. The fore-
leg may be compared to a grappling-iron ; it is extended,
seizes the ground with its claws, and drags the body towards
its point of attachment. The middle leg is chiefly used to
support and steady the body, but has some pushing power.
The hind leg, the largest of the three, is effective in shoving,
and chiefly propels the body.

Muscular Force of Insects.

The force exerted bv Insects has long- been remarked with

surprise, and it is a fact familiar, not only to naturalists, but to
all observant persons, that, making allowance for their small
size, Insects are the most powerful of common animals.

* For example, Prof. Huxley, in his Anatomy of Invertebrated Animals (p. 254),
says that "as the hard skeleton [of Arthropods] is hollow, and the muscles are
inside it, it follows that the body, or a limb, is bent towards that side of its axis,
which is opposite to that on which a contracting muscle is situated." The flexor
muscles of the tail of the Crayfish, which, according to the above rule, should be
extensors, the muscles of the mandibles of an Insect, and the flexors and extensors
of Crustacean pincers are among the many conspicuous exceptions to this rule.

80 THE COCKROACH :

Popular books of natural history give striking and sometimes
exaggerated accounts of the prodigious strength put forth by
captive Insects in their efforts to escape. Thus we are told that
the flea can draw 70 or 80 times its own weight.* The
Cockchafer is said to be six times as strong as a horse, making
allowance for size. A caterpillar of the Goat Moth, imprisoned
beneath a bell-glass, weighing half a pound, which was loaded
with a book weighing four pounds, nevertheless raised the glass
and made its escape.

This interesting subject has been investigated by Plateau, f
who devised the following experiment. The Insect to be
tested was confined within a narrow horizontal channel, which
was laid with cloth. A thread attached to its body was passed
over a light pulley, and fastened to a small pan, into which sand
was poured until the Insect could no longer raise it. Some of
the results are given in the following table : —

Table of Relative Muscular Force of Insects (Plateau).

Weight of body Ratio of weight lifted

in grammes. to weight of body.

Carabus auratus 0*703 ... 17'4

Nebria brevicollis 0'046 ... 25'3

Melolontha vulgaris ... 0'940 ... 14'3
Anomala Frischii 0'153 ... 24'3

Bombus terrestris 0'381 ... 14'9

Apis mellifica 0-090 ... 23'5

One obvious result is that within the class of Insects the
relative muscular force (as commonly understood) is approxi-
mately in the inverse proportion of the weight — that is, the
strength of the Insect is (by this mode of calculation) most
conspicuous in the smaller species.

In a later memoir^ Plateau gives examples from different
Vertebrate and Invertebrate animals, which lead to the same
general conclusion.

* Haller. This and other examples are taken from Rennie's Insect Transformations,
t Bull. Acad. Roy. de Belgique, 2e- Ser., Tom. xx. (1865), and Tom. xxii. (1866).

£ Loc. cit. 3°- Ser., Tom. vii. (1884). Authorities for the various estimates are
cited in the original memoir.

THE MUSCLES J THE FAT-BODY AND CCELOM. 81

Ratio of weight drawn to weight of body (Plateau).

Horse -5 to -83

Man '86

Crab 5-37

Insects 14*3 to 23*5

The inference commonly drawn from, such data is that the

muscles of small animals possess a force which greatly exceeds

that of large quadrupeds or man, allowance being made for size,

and that the explanation of this superior force is to be looked for

in some peculiarity of composition or texture. Gerstaecker,* for

example, suggests that the higher muscular force of Arthropoda

may be due to the tender and yielding nature of their muscles.

An explanation so desperate as this may well lead us to inquire

whether we have understood the facts aright. Plateau's figures

give us the ratio of the weight drawn or raised to the weight

of the animal. This we may, with him, take as a measure of

the relative muscular force. In reality, it is a datum of very

little physiological value. By general reasoning of a quite

simple kind it can be shown that, for muscles possessing the

same physical properties, the relative muscular force necessarily

increases very rapidly as the size of the animal decreases. For

the contractile force of muscles of the same kind depends simply

upon the number and thickness of the fibres, i.e., upon the

sectional area of the muscles. If the size of the animal and of

its muscles be increased according to any uniform scale, the

O ••'

sectional area of a given muscle will increase as the square of
any linear dimension. But the weight increases in a higher
proportion, according to the increase in length, breadth, and
depth jointly, or as the cube of any linear dirnension.f The

* Klassen und Ordnungen des Thierreiclis, Bd. V., pp. 61-2.

t This change in the relation of weight to strength, according to the size of the
structure, has long been familiar to engineers. (See, for example, "Comparisons of
Similar Structures as to Elasticity, Strength, and Stability," by Prof. James
Thomson, Trans. Inst. Engineers, &c., Scotland, 1876.) The application to animal
structures has been made by Herbert Spencer (Principles of Biology, Pt. II., ch. i.).
The principle can be readily explained by models. Place a cubical block upon a
square column. Double all the dimensions in a second model, which may be done
by fitting together eight cubes like the first, and four columns, also the same as before
except in length. Each column, though no stronger than before, has now to bear
twice the weight.

82 THE COCKROACH :

ratio of contractile force to weight must therefore become
rapidly smaller as the size of the animal increases. Plateau's
second table (see above) actually gives a value for the relative
muscular force of the Bee, in comparison with the Horse, which
is only one-fourteenth of what it ought to turn out, supposing
that both animals were of similar construction, and that the
muscular fibres in both were equal in contractile force per unit
of sectional area.*

A later series of experimentsf brings out this difference in a
precise form. Plateau has determined by ingenious methods
what he calls the Absolute Muscular Force^. of a number of
Invertebrate animals (Lamellibranch Mollusca, and Crustacea),
comparing them with man and other Vertebrates. His general
conclusions may be shortly given as follows : — The absolute
muscular force of the muscles closing the pincers of Crabs is

* Contractile force varies as sectional area of muscle. Let W be weight of Horse ;
w, weight of Bee ; R, a linear dimension of Horse ; r, a linear dimension of Bee.

Then,

Contr. force of Horse sect, area of muscles (Horse) 7?2

Contr. force of Bee sect, area of muscles (Bee) r2 '

W R* R* W r
But since - - — -^-, — 5- = • x -^-.
w r3 r2 w R

Contr. force of Horse Wr

Therefore ^ ~r~w ~r>-

Contr. force of Bee wR

But, by definition,

Contr. f. of Horse

Rel. m.f. of Horse W Contr. f. of Horse w

~ReTnuf."orBee~ Contr. f. of Bee Contr. f. of Bee W

w
Wr w r

wR W R

The weight of a horse is about 270,000 grammes, that of a bee '09 gramme ; so that

wf ~~ ' \270 000 r : ( '000'000'3 r = '0015 (nearly) = = Calculated Eatio of

Relative Muscular Force of Horse to that of Bee. The Observed Ratio (Plateau) is

— — — '02128 : so that the relative muscular force of the Horse is more than fourteen

23'5

times as great in comparison with that of the Bee as it would be if the muscles of

both animals were similar in kind, and the proportions of the two animals similar in
all respects.

f Rech. sur la Force Absolue des Muscles des Invertebres. Ie Partie. Mollusques
Lamellibranches. Bull. Acad. Roy. de Belgique, 3e Ser., Tom. VI. (1883).
Do., He Partie. Crustaces Decapodes. Ibid., Tom. VII. (1884).

J Statical muscular force and Specific muscular force are synonymous terms in
common use. Contractile force per unit of sectional area gives perhaps the clearest
idea of what is meant.

THE MUSCLES ; THE FAT-BODY AXD CCELOM. 83

low in comparison with that of Vertebrate muscles. The abso-
lute force of the adductor muscles closing a bivalve shell may,
in certain Lamellibranchs, equal that of the most powerful
Mammalian muscles ; in others it falls below that of the least
powerful muscles of the frog, which are greatly inferior in
contractile force to Mammalian muscles. We find, therefore,
that the low contractile force of Insect muscles is in harmony,
and not in contrast, with common observation of their physical
properties, and that the high relative muscular force, correctly
enough attributed to them, is explicable by considerations which
apply equally well to models or other artificial structures.

The comparison between the muscular force of Insects and
large animals is sometimes made in another way. For example,
in Carpenter's Zoology* the spring of the Cheese-hopper is
described, and we are told that " the height of the leap is often
from twenty to thirty times the length of the body ; exhibiting
an energy of motion which is particularly remarkable in the
soft larva of an Insect. A Viper, if endowed with similar
powers, would throw itself nearly a hundred feet from the
ground." It is here implied that the equation

Height of Insect's leap Supposed ht. of Viper's leap (100 ft.)
Length of Insect Length of Viper

should hold if the two animals were " endowed with similar
powers."

But it is known that the work done by contraction of muscles
'of the same kind is proportional to the volume of the muscles
(" Borelli's Law"),f and in similar animals the muscular
volumes are as the weights. Therefore the equation

Work of Insect • Work of Viper
Weight of Insect Weight of Viper

will more truly represent the imaginary case of equal leaping
power. But the work = weight raised X height, and the weight
raised is in both cases the weight of the animal itself. Therefore

Wt. x Ht. Wt. x Ht.

^\vtT " (Insect) : "WtT " ^ lper)'

' Vol. II., p. 203. The calculation here quoted is based upon an observation of
Swammerdam, who relates that a Cheese-hopper, 5 in. long, leaped out of a box
6 in. deep.

t Haughton's Animal Mechanics, 2nd ed., p. 43.

84 THE COCKROACH :

and Ht. (Insect) = Ht. (Viper). The Viper's efficiency as a
leaping animal would, therefore, equal that of a Cheese-hopper
if it leaped the same vertical height. Therefore, if. the two
animals were "endowed with similar powers," the heights to
which they could leap would be equal, and not proportional to
their lengths, as is assumed in the passage quoted.

Straus-Diirckheim observes that a Flea can leap a foot high,
which is 200 times its own length, and this has been considered
a stupendous feat. It is really less remarkable than a school-
boy's leap of two feet, for it indicates precisely as great
efficiency of muscles and other leaping apparatus as would be
implied in a man's leap to the same height, viz., one foot.*

The Fat-both/.

Adhering to the inner face of the abdominal wall is a cellular
mass, which forms an irregular sheet of dense white appearance.
This is the fat-body. Its component cells are polygonal, and
crowded together. When young they exhibit nuclei and
vacuolated protoplasm, but as they get older the nuclei dis-
appear, the cell-boundaries become indistinct, and a fluid, loaded
with minute refractive granules, f takes the place of the living-
protoplasm. Rhombohedral or hexagonal crystals, containing
uric acid, form in the cells and become plentiful in old tissue.
The salt (probably urate of soda) is formed by the waste of
the proteids of the body. What becomes of it in the end we
do not know for certain, but conjecture that it escapes by the
blood which bathes the perivisceral cavity, that it is taken up
again by the Malpighian tubules, and is finally discharged into
the intestine. The old gorged cells probably burst from time to
time, and the infrequency of small cells among them renders it
probable that rejuvenescence takes place, the burst cells passing
through a resting-stage, accompanied by renewal of their
nuclei, and then repeating the cycle of change.

The segmental tubes forming the Wolffian body of Verte-
brates have at first no outlet, and embryologists have hesitated

* In any comparison it is necessary to cite not the height cleared by the man, but
the displacement during the leap of his centre of gravity.

t The granules are not shown in the figure, having been removed in the prepara-
tion of the tissue for microscopic examination.

THE MUSCLES ; THE FAT-BODY AXD CCELOM.

to regard this phase of development as the permanent condition
of any ancestral form.* It is, therefore, of interest to find in
the fat-body of the Cockroach an example of a solid, meso-
blastic, excretory organ, functional throughout life, but without
efferent duct.

Fig. 38. —Fat-body of Cockroach, cleared with turpentine. A, young tissue, with
distinct cell-boundaries and nuclei, a few cells towards the centre with dead
contents ; JS, older ditto, loaded with urates, the cell- walls much broken down,
and the nuclei gone ; tr, tracheal tubes. X 250.

The fat-body is eminently a metabolic tissue, the seat of
active chemical change in the materials brought by the blood.

Its respiratory needs are attested by the abundant air-tubes
which spread through it in all directions.

The considerable bulk of the fat-body in the adult Cockroach
points to the unusual duration of the perfect Insect. It is
usually copious in full-fed larvae, but becomes used up in the
pupa- stage.

Extensions of the fat-body surround the nervous chain, the
reproductive organs and other viscera, Sheets of the same
substance lie in the pericardial sinus on each side of the heart.

The Coelom.

The fat-body is in reality, as development shows, the irregular
cellular wall of the coelom, or peri visceral space. Through
this space courses the blood, flowing in no defined vessels, but
bathing all the walls and viscera. In other words, the fat-body

is an aggregation of little-altered mesoblast-cells, excavated by
the coelom, the rest of the mesoblast having gone to form the

O o

muscular layers of the body-wall and of the digestive tube.

«. •,

* Balfour, Embryology, Vol. II., p. 003.

CHAPTER VI.

THE NERVOUS SYSTEM AND SENSE ORGANS.

SPECIAL REFERENCES.

NEWPORT. Nervous System of Sphinx Ligustri. Phil. Trans. (1832-4). Todd's
Cyclopedia, Art. "Insecta" (1839).

LEYDIG. Vom Bau des Thierischen Kb'rpers. Bd. I. (1804). Tafeln zur. vergl.
Anat. Hft. I. (1864).

BRANDT (E.). Various memoirs on the Nervous System of Insects in Horse Soc.
Entom. Ross., Bd. XIV., XV. (1879).

MICHELS. Nerveusystem von Oryctes nasicornis im Larven — , Puppen — , und
Kaferzustande. Zeits. f. wiss. Zool., Bd. XXXIV. (1881).

DlETL. Organisation des Arthropodeugehirns. Zeits. f. wiss. Zool., Bd. XXVII.
(187G).

FLOGEL. Bau des Gehirns der verschiedenen Insektenordnungen. Zeits. f. wiss.
Zool., Bd. XXX. Sup. (1878).

NEWTON. On the Brain of the Cockroach. Q. J. Micr. Sci. (1879). Journ.
Quekett Club (1879).

GRENACBER. Sehorgan der Arthropoden. (1879). [Origin, Structure, and Action
of the Compound Eye.]

CARRIERE. Sehorgane der Thiere, vergl. -anat. dargestellt (1885). [Comparative
Structure of various Simple and Compound Eyes.]

General Anatomy of Nervous Centres.

THE nervous system of the Cockroach comprises ganglia and
connectives,* which extend throughout the body. We have,
first, a supra-oesophageal ganglion, or brain, a sub-cesophageal
ganglion, and connectives which complete the cesophageal ring.
All these lie in the head ; behind them, and extending through
the thorax and abdomen, is a gangliated cord, with double
connectives. The normal arrangement of the ganglia in
Annulosa, one to each somite, becomes more or less modified in
Insects by coalescence or suppression, and we find only eleven
ganglia in the Cockroach — viz., two cephalic, three thoracic,
and six abdominal.

•Yung ("Syst. nerveux des Crustacees Decapodes, Arch, de Zool. exp. et gen.,"
Tom. VII., 1878) proposes to name connectives the longitudinal bundles of nerve-fibres
which unite the ganglia, and to reserve the term commissures for the transverse

communicating branches.

THE COCKROACH : ITS NERVOUS SYSTEM.

Fig. 39.— Nervous System of Female Cockroach, x G. a, optic nerve ; b, antennary
nerve ; c, d, e, nerves to first, second, and third legs ; /, to wing-cover ; g, to
second thoracic spiracle ; h, to wing ; i, abdominal nerve ; j, to cerci.

THE COCKROACH :

The nervous centres of the head form a thick, irregular ring,
which swells above and below into ganglionic enlargements,
and leaves only a small central opening, occupied by the
oesophagus. The tentorium separates the brain or supra-
cesophageal ganglion from the sub-cesophageal, while the
connectives traverse its central plate. Since the oesophagus
passes above the plate, the investing nervous ring also lies
almost wholly above the tentorium.

Fig. 40.— Side view of Brain of Cockroach, X 25. op, optic nerve; oe, oesophagus;
t, tentorium; sb, sub-oesophageal ganglion; mn, mx, mx', nerves to mandible
and maxillae. Copied from E. T. Newton.

The brain is small in comparison with the whole head ; it
consists of two rounded lateral masses or hemispheres, incom-
pletely divided by a deep and narrow median fissure. Large
optic nerves are given off laterally from the upper part of each
hemisphere ; lower down, and on the front of the brain, are the
two gently rounded antennary lobes, from each of which
proceeds an antennary nerve ; while from the front and upper
part of each hemisphere a small nerve passes to the so-called
"ocellus/' a transparent spot lying internal to the antennary

ITS NERVOUS SYSTEM AND SENSE ORGANS. 89

socket on each side in the suture between the clypeus and the
epicranium. The sub-oesophageal ganglion gives off branches
to the mandibles, maxilla), and labrum. While, therefore, the
supra-cesophageal is largely sensory, the sub-oesophageal gang-
lion is the masticatory centre.

The cesophageal ring is double below, being completed by the
connectives and the sub-oesophageal ganglion; also by a smaller
transverse commissure, which unites the connectives, and applies
itself closely to the under-surface of the oesophagus.*

Two long connectives issue from the top of the sub-
oesophageal ganglion, and pass between the tentorium and the
submentum on their way to the neck and thorax. The three
thoracic ganglia are large (in correspondence with the important
appendages of this part of the body) and united by double
connectives. The six abdominal ganglia have also double
connectives, which are bent in the male, as if to avoid
stretching during forcible elongation of the abdomen. The
sixth abdominal ganglion is larger than the rest, and is no
doubt a complex, representing several coalesced posterior
ganglia ; it supplies large branches to the reproductive organs,
rectum, and cerci.

Internal Structure of Ganglia.

Microscopic examination of the internal structure of the
nerve-cord reveals a complex arrangement of cells and fibres.
The connectives consist almost entirely of nerve-fibres, which,
as in Invertebrates generally, are non-medullated. The ganglia
include (1) rounded, often multipolar, nerve-cells ; (2) tortuous
and extremely delicate fibres collected into intricate skeins ;
(3) commissural fibres, and (4) connectives. The chief fibrous
tracts are internal, the cellular masses outside them. A rela-
tively thick, and very distinct neurilemma, probably chitinous,
encloses the cord. Its cellular matrix, or chitinogenous layer,

This commissure, which has- been erroneously regarded as characteristic of
Crustacea, was found by Lyonnet in the larva of Cossus, by Straus-Diirckheim in
Locusta and Buprestis, by Blanchard in Dytiscus and Otiorhynchus, by Leydig in
Glomeris and Telephorus, by Dietl in Gryllotalpa, and by Lienard in a large number
of other Insects and Myriapods, including Periplaneta. See Lienard, "Const, de
1'anneau cesophagien," Bull. Acad. Roy. de Belgique, 2'- Ser., Tom. XLIX., 1880.

THE COCKROACH :

is distinguished by the elongate nuclei of its constituent cells.*
Tracheal trunks pass to each ganglion, and break up upon and
within it into a multitude of fine branches.

Fig. 41. — Transverse section of Third Thoracic Ganglion, neu, neurilemmar cells ;
gc, ganglionic cells ; tr, tracheal tubes ; A, ganglionic cells, highly magnified.
X 75.

n e u

Fig. 42. — Longitudinal vertical section of Third Thoracic Ganglion, n, connective.

The other references as in fig. 41. X 75.

Bundles of commissural fibres pass from the ganglion cells of
one side of the cord to the peripheral nerves of the other.
There are also longitudinal bands which blend to form the
connectives, and send bundles into the peripheral nerves. Of

* We have not been able to distinguish in the adult Cockroach the double layer of
neurilemmar cells noticed by Leydig and Michels in various Coleoptera.

ITS NERVOUS SYSTEM AND SENSE ORGANS.

the peripheral fibres, some are believed to pass direct to their
place of distribution, while others traverse at least one complete
segment and the corresponding ganglion before separating from
the cord.

•^-iVTTv * --~V . -i <\

Fig. 43.- Longitudinal horizontal section of Third Thoracic Ganglion, n, peripheral
nerves. The other references as before. X 75.

Many familiar observations show that the ganglia of an
Insect possess great physiological independence. The limbs of
decapitated Insects, and even isolated segments, provided that
they contain uninjured ganglia, exhibit unmistakable signs of
life.

92 THE COCKROACH :

Median Nerve- Cord.

Lyonnet,* Newport, f and LeydigJ have found in large
Insects a s}Tstem of median nerves, named respiratory (Newport)
or sympathetic (Leydig). These nerves do not form a continuous
cord extending throughout the body, but take fresh origin
in each, segment from the right and left longitudinal commis-
sures alternately. The median nerve lies towards the dorsal
side of the principal nerve-cord, crosses over the ganglion next
behind, and receives a small branch from it. Close behind the
ganglion it bifurcates, the branches passing outwards and
blending with the peripheral nerves. Each branch, close to its
origin, swells into a ganglionic enlargement. The median
nerve and its branches differ in appearance and texture from
ordinary peripheral nerves, being more transparent, delicate,
and colourless. They are said to supply the occlusor muscles of
the stigmata. In the Cockroach, the median nerves are so
slightly developed in the thorax and abdomen (if they
actually exist) that they are hardly discoverable by ordinary
dissection. We have found only obscure and doubtful traces
of them, and these only in one part of the abdominal nerve-
cord. The stomato-gastric nerves next to be described
appear to constitute a peculiar modification of that median
nerve- cord which springs from the circum-cesophageal
connectives.

Sto mato -gastric Net ves .

In the Cockroach the stomato-gastric nerves found in so
many of the higher Invertebrates are conspicuous!}7 developed.
From the front of each oesophageal connective, a nerve passes
forwards upon the oesophagus, outside the chitinous crura of the
tentorium. Each nerve sends a branch downwards to the
labrum, and the remaining fibres, collected into two bundles,
join above the oesophagus to form a triangular enlargement, the

* Traite Anat., p. 201, pi. ix., fig. 1.
t Phil. Trans., 1834, p. 401, pi. xvi.

I Vom Bau des Thierisclien Korpers, pp. 203, 262; Taf. z. vergl. Anat., pi. vi.,
tig. 3.

ITS NERVOUS SYSTEM AND SENSE ORGANS.

' 93

frontal ganglion. From this ganglion a recurrent nerve passes
backwards through the o?sophageal ring, and ends on the dorsal
surface of the crop (*3 inch from the ring), in a triangular

Fig. 44. — Stomato-gastric Xerves of Cockroach, f )'•(/., frontal ganglion; at., anten-
nary nerve; conn., connective; pa.y., paired ganglia; /•.//., recurrent nerve;
r.'j., ventricular ganglion.

ganglion, from which a nerve is given off outwards and back-
wards on either side. Each nerve bifurcates, and then breaks
up into branches which are distributed to the crop and gizzard.*
Just behind the oesophageal ring, the recurrent nerve forms a

* The stomato-gastric nerves of the Cockroach have been carefully described l>v
Koestler (Zeits. f. wiss. Zool., Bd. XXXIX., p. 592).

94 THE COCKROACH :

plexus with a pair of nerves which proceed from the back of
the brain. Each nerve forms two ganglia, one behind the
other, and each ganglion sends a branch inwards to join the
recurrent nerve. Fine branches proceed from the paired nerves
of the ocsophageal plexus to the salivary glands.

The stomato-gastric nerves differ a good deal in different
insects ; Brandt* considers that the paired and impaired nerves
are complementary to each other, the one being more elaborate,
according as the other is less developed. A similar system is
found in Mollusca, Crustacea, and someVermes (e.#.,Nemerteans).
When highly developed, it contains unpaired ganglia and
nerves, but may be represented only by an indefinite plexus
(earthworm). It always joins the cesophageal ring, and sends
branches to the oesophagus and fore-part of the alimentary canal.
The system has been identified with the sympathetic, and also
with the vagus of Vertebrates, but such correlations are hazar-
dous ; the first, indeed, may be considered as disproved.

Internal Structure of Brain.

The minute structure of the brain has been investigated by
Leydig, Dietl, Flogel, and others, and exhibits an unexpected
complexity. It is as yet impossible to reduce the many curious
details which have been described to a completely intelligible
account. The physiological significance, and the homologies
of many parts are as yet altogether obscure. The comparative
study of new types will, however, in time, bridge over the wide
interval between the Insect-brain and -the more familiar Verte-
brate-brain, which is partially illuminated by physiological
experiment. Mr. E. T. Newton has published a clear and
useful description f of the internal and external structure of the
brain of the Cockroach, which incorporates what had previously
been ascertained with the results of his own investigations. He
has also described J an ingenious method of combining a
number of successive sections into a dissected model of the

* "Mem. Acad. Petersb.," 1835.

f "Q. J. Micr. Sci.," 1879, pp. 340-350, pi. xv., xvi.

I " Jouvn. Quekett Micr. Club," 1879.

ITS NERVOUS SYSTEM AXD SENSE ORGANS.

brain. Having had the advantage of comparing the model with
the original sections, we offer a short abstract of Mr. Newton's
memoir as the best introduction to the subject. He describes
the central framework of the Cockroach brain as consisting of
two solid and largely fibrous trabeculce, which lie side by side
along the base of the brain, becoming smaller at their hinder
ends ; they meet in the middle line, but apparently without
fusion or exchange of their fibres. Each trabecula is continued
upwards by two fibrous columns, the cauliculus in front, and the
peduncle behind ; the latter carries a pair of cellular disks, the

OCX.

OCX*

Fig. 45. —A, lobes of the brain of the Cockroach, seen from within ; c, cauliculus;
p, peduncle ; t, trabecula. B, ditto, from the front ; ocx, outer calyx ; icx, inner
calyx. C, ditto, from above. Copied from E. T. Newton.

calices (the cauliculus, though closely applied to the calices, is
not connected with them) ; these disks resemble two soft cakes
pressed together above, and bent one inwards, and the other
outwards below. The peduncle divides above, and each branch
joins one of the calices of the same hemisphere.

This central framework is invested by cortical ganglionic
cells, which possess distinct nuclei and nucleoli. A special
cellular mass forms a cap to each pair of calices, and this

THE COCKROACH

an—-

com-

Fig. 4(5. — Model of Cockroach Brain, constructed from slices of wood representing

successive sections.

com,

Fig. 47. — Right half of Model-brain seen from the inner side, with the parts dissected
away, so as to show the anterior nervous mass (cauliculus). a; the median mass
(tralecula), m ; the mushroom-bodies (caliccs), mb; and their stems (peduncles),
st. The cellular cap, c, has been raised, so as to display the parts below : com,
is a part of the connective uniting the brain and infra-cesophageal ganglia.
[Figs. 45-48 are taken from Mr. E. T. Newton's paper in "Jouru. Quekett
Club," 1879.]

ITS NERVOUS SYSTEM AND SENSE ORGANS.

7TL

-in

Fig. 48. — Diagrammatic outlines of sections of the Brain of a Cockroach. Only one
side of the brain is here represented. The numbers indicate the position in the
series of thirty-four sections into which this brain was cut. al, antennary lobe;
'nib, mushroom bodies (calices), with their cellular covering, c, and their stems
(peduncles), st; a, anterior nervous mass (cauliculus) ; m, median nervous mass
(trabecula). From E. T. Newton.

THE COCKROACH :

consists of smaller cells without nucleoli. Above the meeting-
place of the trabeculoe is a peculiar laminated mass, the central
body, which consists of a network of fibres continuous with the
neighbouring ganglionic cells, and enclosing a granular sub-
stance. The antennary lobes consist of a network of fine fibres

'OC

Fig. 49. — Frontal section of Brain of Cockroach. C, cellular layer beneath neuri-
lemma; ICx, inner calix ; O Cx, outer calix ; GO, ganglion-cells ; P, peduncle ;
T, trabecula; Op, optic nerve ; AnL, antennary lobe. X 24.

enclosing ganglion cells, and surrounded by a layer of the
same. It is remarkable that no fibrous communications can be
made out between the calices and the cauliculi, or between the
trabeculse and the oesophageal connectives.

Sense Organs. The Eye of Insects.

The sense organs of Insects are very variable, both in position
and structure. Three special senses are indicated by trans-
parent and refractive parts of the cuticle, by tense membranes
with modified nerve-endings, and by peculiar sensory rods or

ITS NERVOUS SYSTEM AND SENSE ORGANS.

filaments upon the antennae. These are taken to be the organs
respectively of sight, hearing, and smell. Other sense organs,
not as yet fully elucidated, may co-exist with these. The
maxillary palps of the Cockroach, for example, are continually
used in exploring movements, and may assist the animal to
select its food ; the cerci, where these are well-developed, and
the halteres of Diptera, have been also regarded as sense organs
of some undetermined kind, but this is at present wholly
conjecture.*

Fig. 50. — Plan of Eye of Cockroach, showing the number of facets along
the principal diameters, as, antennary socket.

The compound eyes of the Cockroach occupy a large, irregu-
larly oval space (see fig. 50) on each side of the head. The
total number of facets may be estimated at about 1,800. The
number is very variable in Insects, and may either greatly
exceed that found in the Cockroach, or be reduced to a very
small one indeed. According to Burmeister, the Coleopterous
genus Mordella possesses more than 25,000 facets. Where the
facets are very numerous, the compound eyes may occupy
nearly the whole surface of the head, as in the House-fly
Dragon-fly, or Gad-fly.

Together with compound eyes, many Insects are furnished
also with simple eyes, usually three in number, and disposed in

* It is to be remarked that unusually large nerves supply the cerci of the Cockroach.

100

THE COCKROACH :

a triangle on the forehead. The white fenestrsc, which in the
Cockroach lie internal to the antennary sockets, may represent
two simple eyes which have lost their dioptric apparatus. In
many larvae only simple eyes are found, and the compound eye
is restricted to the adult form ; in larval Cockroaches, however,
the compound eye is large and functional.

Co.F

Cr-

Fig. 51.— One element of the Compound Eye of the Cockroach, X 700. Co. F.
corneal facets; Cr, crystalline cones; Em, nerve-rod (rhabdom); HI, retinula
of protoplasmic fibrils. To the right are transverse sections at various levels.
Copied from Grenadier.

Each facet of the compound eye is the outermost element of a
series of parts, some dioptric and some sensory, which forms
one of a mass of radiating] rods or fibres. The facets are

ITS NERVOUS SYSTEM AND SEXSE ORGANS.

101

transparent, biconvex, and polygonal, often, but not quite
regularly, hexagonal. In many Insects the deep layer of each
facet is separable, and forms a concavo-convex layer of different
texture from the superficial and biconvex lens. The facets,
taken together, are often described as the cornea ; they repre-
sent the chitinous cuticle of the integument. The subdivision
of the cornea into two layers of slightly different texture
suggests an achromatic correction, and it is quite possible,
though unproved, that the two sets of prisms have different
dispersive powers. Beneath the cornea we find a layer of
crystalline cones, each of which rests by its base upon the inner
surface of a facet, while its apex is directed inwards towards

Fig. 52. — Diagram of Insect Integument, in section, bm, basement-membrane ;
hyp, hypodermis, or chitinogenous layer ; ct, cl', chitinous cuticle ; s, a seta.

the brain. The crystalline cones are transparent, refractive,
and coated with dark pigment ; in the Cockroach they are
comparatively short and blunt. Behind each cone is a nerve-
rod (rhabdom), which, though outwardly single for the greater
part of its length, is found on cross-section to consist of four
components (rhabdomeres)* ; these diverge in front, and receive
the tip of a cone, which is wedged in between them ; the
nerve-rods are densely pigmented. The rhabdom is invested by
a protoplasmic sheath, which is imperfectly separated into

* The number in Insects varies from eight to four, but seven is usual ; four is the
usual number in Crustacea.

102

THE COCKROACH :

segments (retinulce), corresponding in number with the rhab-
domeres. Each retinula possesses at least one nucleus. The
retinuke were found by Leydig to possess a true visual purple.
To the hinder ends of the retinulaB are attached the fibres of
the optic nerve, which at this point emerges through a " fene-
strated membrane/'

In the simple eye the non-faceted cornea and the retinula are
readily made out, but the crystalline cones are not developed

•N.Op

Fig. 53. — Section through Eye of Dytiscus-larva, showing the derivation of the
parts from modified hypodermic cells. L, lens ; Or, crystalline cones ; R, nerve -
rods ; N. Op. optic nerve. From Grenacher.

as such. The morphological key to both structures is found in
the integument, of which the whole eye, simple or compound, is
a modification. A defined tract of the chitinous cuticle becomes
transparent, and either swells into a lens (fig. 53), or becomes
regularly divided into facets (fig. 55), which are merely the
elaboration of imperfectly separated polygonal areas, easily
recognised in the young cuticle of all parts of the body. 'Next,
the chitinogenous layer is folded inwards, so as to form a cup,
and this, by the narrowing of the mouth, is transformed into a
flask, and ultimately into a solid two-layered cellular mass (fig.
53). The deep layer undergoes conversion into a retina, its
chitinogenous cells developing the nerve-rods as interstitial
structures, while the superficial layer, which loses its functional

ITS NERVOUS SYSTEM AND SENSE ORGANS.

103

importance in the simple eye, gives rise by a similar process of
interstitial growth to the crystalline cones of the compound eye
(fig. 55). The basement-membrane, underlying the chitin-
ogenous cells, is transformed into the fenestrated membrane.
The nerve-rods stand upon it, like organ pipes upon the sound-
board, while fibrils of the optic nerve and fine tracheae pass
through its perforations. The mother-cells of the crystalline
cones and nerve-rods are largely replaced by the interstitial
substances they produce, to which they form a sheath ; they are
often loaded with pigment, and the nuclei of the primitive-cells
can only be distinguished after the colouring-matter has been
discharged by acids or alkalis.

Fig. 54. — Section through Simple Eye of Vespa. The references as above.

Simplified from Grenacher.

Dr. Hickson* has lately investigated the minute anatomy of
the optic tract in various Insects. He finds, in the adult of the
higher Insects, three distinct ganglionic swellings, consisting of
a network of fine fibrils, surrounded by a sheath of crowded
nerve-cells. Between the ganglia the fibres usually decussate.
In the Cockroach, and some other of the lower Insects, the

* "Q. J. Micr. ScL," 1885.

104

THE COCKROACH :

outermost ganglion is undeveloped. The fibres connecting the
second ganglion with the eye take a straight course in the
young Cockroach, but partially decussate in the adult.

All the parts between the crystalline cones and the true optic
nerve are considered by Hickson to compose the retina of
Insects, which, instead of ending at the fenestrated-membrane,
as has often been assumed, includes the ganglia and decussating
fibres of the optic tract. The layer of retinulae and rhabdoms
does not form the whole retina, but merely that part which, in
the vertebrate eye, is known as the layer of rods and cones.

brrv

N.Op

Fig. 55. — Diagrammatic section of Compound Eye. The references as above.

As to the way in which the compound eye renders distinct
vision possible, there is still much difference of opinion. A
short review of the discussion which has occupied some of the
most eminent physiologists and histologists for many years
past will introduce the reader to the principal facts which have
to be reconciled.

The investigation, like so many other trains of biological
inquiry, begins with Leeuwenhoeck (Ep. ad Soc. Reg. Angl. iii.),
who ascertained that the cornea of a shardborne Beetle, placed

ITS NERVOUS SYSTEM AND SENSE ORGANS. 105

in the field of a microscope, gives images of surrounding objects,
and that these images are inverted. When the cornea is
flattened out for microscopic examination, the images (e.g., of a
window or candle-flame) are similar, and it has been too hastily
assumed that a multitude of identical images are perceived by
the Insect. The cornea of the living animal is, however,
convex, and the images formed by different facets cannot be

CJ »/

precisely identical. JN"o combined or collective image is formed
by the cornea. When the structure of the compound eye had
been very inadequately studied, as was the case even in Cuvier's
time (Lecons d'Anat. Comp., xii., 14), it was natural to suppose
that all the fibres internal to the cornea were sensory, that they
formed a kind of retina upon which the images produced by the
facets were received, and that these images were transmitted to
the brain, to be united, either by optical or mental combination,
into a single picture. Miiller,* in 1826, pointed out that so
simple an explanation was inadmissible. He granted that the
simple eye, with its lens and concave retina, produces a single
inverted image, which is able to affect the nerve-endings in the
same manner as in Vertebrates. But the compound eye is not
optically constructed so as to render possible the formation of
continuous images. The refractive and elongate crystalline

cones, with their pointed apices and densely pigmented sides,
must destroy any images formed by the lenses of the cornea.
Even if the dioptric arrangement permitted the formation of
images, there is no screen to receive them.f Lastly, if this
difficulty were removed, Miiller thought it impossible for the
nervous centres to combine a great number of inverted partial
images. How then can Insects and Crustaceans see with their
compound eyes? Miiller answered that each facet transmits a
small pencil of rays travelling in the direction of its axis, but
intercepts all others. The refractive lens collects the rays, and
the pigmented as well as refractive crystalline cone further
concentrates the pencil, while it stops out all rays which diverge
appreciably from the axis. Each element of the compound eye
transmits a single impression of greater or less brightness, and

Exner has since determined by measurement and calculation the optical
properties of the eye of Hydro philus. He finds that the focus of a corneal lens is
about 3mm. away, and altogether behind the eye.
f Zur vergl. Phys. des Gesichtsinnes.

106 THE COCKROACH.

the brain combines these impressions into some kind of picture,
a picture like that which could be produced by stippling. It
may be added that the movements of the insect's head or body
would render the distance and form of every object in view
much readier of appreciation. No accommodation for distance
would be necessary, and the absence of all means of accommoda-
tion ceases to be perplexing. Such is Miiller's theory of what he
termed " mosaic vision." Many important researches, some
contradictory, some confirmatory of Miiller's doctrine,* have
since been placed on record, with the general result that some
modification of Miiller's theory tends to prevail. The most
important of the new facts and considerations which demand
attention are these : —

Reasons have been given for supposing that images are formed
by the cornea and crystalline cones together. This was first
pointed out by Gottsche (1852), who used the compound eyes of
Flies for demonstration. Grenacher has since ascertained that
the crystalline cones of Flies are so fluid that they can hardly
be removed, and he believes that Gottsche's images were formed
by the corneal facets alone. He finds, however, that the
experiment may be successfully performed with eyes not liable
to this objection, e.g., the eyes of nocturnal Lepidoptera. A bit
of a Moth's eye is cut out, treated with nitric acid to remove the
pigment, and placed on a glass slip in the field of the micro-
scope. The crystalline cones, still attached to the cornea, are
turned towards the observer, and one is selected whose axis
coincides with that of the microscope. No image is visible
when the tip of the cone is in focus, but as the cornea
approaches the focus, a bristle, moved about between the mirror
and the stage, becomes visible. This experiment is far from
decisive. No image is formed where sensory elements are
present to receive and transmit it. Moreover, the image is
that of an object very near to the cornea, whereas all observa-
tions of living Insects show that the compound eye is used for
far sight, and the simple eye for near sight. Lastly, the treat-
ment with acid, though unavoidable, may conceivably affect the

* A critical history of the whole discussion is to be found in Grenacher's "Seh-
organ der Arthropoden" (1879), from which we take many historical and structural
details.

ITS NERVOUS SYSTEM AND SENSE ORGANS. 107

result. It is not certain that the cones really assist in the

production of the image, which may be due to the corneal
facets alone, though modified by the decolorised cones.

Grenacher has pointed out that the composition of the nerve-
rod furnishes a test of the mosaic theory. According as the
percipient rod is simple or complex, we may infer that its
physiological action will be simple or complex too. The
adequate perception of a continuous picture, though of small
extent, will require many retinal rods ; on the other hand, a
single rod will suffice for the discrimination of a bright point.
What then are the facts of structure ? Grenacher has ascer-
tained that the retinal rods in each element of the compound
eye rarely exceed seven, and often fall as low as four — further,
that the rods in each group are often more or less completely
fused so as to resemble simple structures, and that this is
especially the case with Insects of keen sight.*

Certain facts described by Schultze tell on the other side.
Coming to the Arthropod eye, fresh from his investigation of
the vertebrate retina, Schultze found in the retinal rods of
Insects the same lamellar structure which he had discovered in
Yertebrata. He found also that in certain Moths, Beetles, and
Crustacea, a bundle of extremelv fine fibrils formed the outer

extremity of each retinal or nerve-rod. This led him to reject
the mosaic theory of vision, and to conclude that a partial image
was formed behind every crystalline cone, and projected upon a
multitude of fine nerve-endings. Such a retinula of delicate
fibrils has received no physiological explanation, but it is
now known to be of comparatively rare occurrence ; it has
no pigment to localise the stimulus of light ; and there is
no reason to suppose that an image can be formed within its
limits.

The optical possibility of such an eye as that interpreted to
us by Miiller has been conceded by physicists and physiologists
so eminent as Helmholz and Du Bois Reymond. Nevertheless,
the competence of any sort of mosaic vision to explain the
precise and accurate perception of Insects comes again and
again into question whenever we watch the movements of a

* Flies, whose eyes are in several respects exceptional, have almost completely
separated rods, notwithstanding their quick sight.

108 THE COCKROACH :

House-fly as it avoids the hand, of a Bee flying from flower to
flower, or of a Dragon-fly in pursuit of its prey. The sight of
such Insects as these must range over several feet at least, and
within this field they must be supposed to distinguish small
objects with rapidity and certainty. How can we suppose that
an eye without retinal screen, or accommodation for distance, is
compatible with sight so keen and discriminating ? The answer
is neither ready nor complete, but our o\vn eyesight shows how
much may be accomplished by means of instruments far from
optically perfect. According to Aubert, objects, to be perceived
as distinct by the human eye, must have an angular distance of
from 50" to 70", corresponding to several retinal rods. Our
vision is therefore mosaic too, and the retinal rods which can
be simultaneously affected comprise only a fraction of those
contained within the not very extensive area of the effective
retina. Still we are not conscious of any break in the con-
tinuity of the field of vision. The incessant and involuntary
movements of the eyeball, and the appreciable duration of the
light-stimulus partly explain the continuity of the image
received upon a discontinuous organ. Even more important is
the action of the judgment and imagination, which complete
the blanks in the sensorial picture, and translate the shorthand
of the retina into a full-length description. That much of what
we see is seen by the mind only is attested by the inadequate
impression made upon us by a sudden glimpse of unfamiliar
objects. We need time and reflection to interpret the hints
flashed upon our eyes, and without time and reflection we see
nothing in its true relations. The Insect-eye may be far from
optical perfection, and yet, as it ranges over known objects, the
Insect-mind, trained to interpret colour, and varying bright-
ness, and parallax, may gain minute and accurate information.
Grant that the compound eye is imperfect, and even rude, if
regarded as a camera ; this is not its true character. It is
intended to receive and interpret flashing signals ; it is an
optical telegraph.

Plateau* has recently submitted the seeing powers of a
number of different Insects to actual experiment. The two
windows of a room five metres square were darkened. An

* Bull, de 1'Acacl. Roy. de Belgique, 1885.

ITS NERVOUS SYSTEM AND SENSE ORGANS. 109

aperture fitted with ground glass was then arranged in each
window. At a distance of four metres from the centre of the
space between the windows captive Insects were from time to
time liberated. One of the windows was fenced with fine trellis,
so as to prevent the passage of the Insect, or otherwise altered
in form, but the size of the aperture could be increased at
pleasure, so as exactly to make up for any loss of light caused
thereby, the brightness of the two openings being compared by
a photometer.

It was found that day-flying Insects require a tolerably good
light ; in semi-obscurity they cannot find their way, and often
refuse to fly at all. By varnishing one or other set in Insects
possessing both simple and compound eyes, it was found that
day-flying Insects provided with compound eyes do not use their
simple eyes to direct their course. TThen the light from one
window was sensibly greater than that from the other, the
Insect commonly chose the brightest, but the existence of bars,
close enough to prevent or to check its passage, had no per-
ceptible effect upon the choice of its direction. Alterations in the
shape of one of the panes seemed to be immaterial, provided
that the quantity of light passing through remained the same,
or nearly the same. Plateau concludes that Insects do not
distinguish the forms of objects, or distinguish them very
imperfectly.

It is plain, and Plateau makes this remark himself, that such
experiments upon the power of unaided vision in Insects, give a
very inadequate notion of the facility with which an Insect
flying at large can find its way. There the animal is guided by
colour, smell, and the actual or apparent movements of all
visible objects. Exner has pointed out how important are the
indications o-iven by movement. Even in man, the central

^j */

part of the retina is alone capable of precise perception of
form, but a moving object is observed by the peripheral tract.
Plateau (from whom this quotation is made) adds that most
animals are very slightly impressed by the mere form of
their enemies, or of their prey, but the slightest movement
attracts their notice. The sportsman, the fisherman, and the
entomologist cannot fail to learn this fact by repeated and
cogent proofs.

110 THE COCKROACH:

Sense of Smell in Insects.

The existence of a sense of smell in Insects has probably
never been disputed. Many facts of common observation prove
that carrion-feeders, for example, are powerfully attracted
towards putrid animal substances placed out of sight. The
situation of the olfactory organs has only been ascertained by
varied experiments and repeated discussion. Rosenthal, in
1811, and Lefebvre, in 1838, indicated the antennae as the
organs of smell, basing their conclusions upon physiological
observations made upon living insects. Many entomologists of
that time were inclined to regard the antennae as auditory
organs.* Observations on the minute structure of the antennae
were made by many workers, but for want of good histological
methods and accurate information concerning the organs of
smell in other animals, these proved for a long time indecisive.
It was by observation of living insects that the point was
actually determined.

«/

Hauser's experiments, though by no means the first, are the
most .instructive which we possess. He found that captive
insects, though not alarmed by a clean glass rod cautiously
brought near, became agitated if the same rod had been first
dipped in carbolic acid, turpentine, or acetic acid. The antennae
performed active movements while the rod was still distant, and
after it was withdrawn the insect was observed to wipe its
antennae by drawing them through its mouth. After the
antennae had been extirpated or coated with parainn, the same
insects became indifferent to strong-smelling substances, though
brought quite near. Extirpation of the antennae prevented flies
from discovering putrid flesh, and hindered or prevented copu-
lation in insects known to breed in captivity.

Following up these experiments by histological investigation
of many insects belonging to different orders, Hauser clearly
established the following points, which had been partially made
known before : —

The sensory elements of the antennae are lodged in grooves
or pits, which may be filled with fluid. The nerve-endings are
associated with peculiar rods, representing modified chitino-

* References to the literature of the question are given by Hauser in Zeits. f. wiss.
Zool., Bd. XXXIV., and by Plateau in Bull. Soc. Zool. de France, Tom. X.

ITS NERVOUS SYSTEM AND SENSE ORGANS. Ill

genous cells. The number of grooves or pits may be enormous.
In the male of the Cockchafer, Hauser estimates that there are
39,000 in each antenna. He remarks that in all cases where
the female Insect is sluggish and prone to concealment, the
male has the antennae more largely developed than the female.

Sense of Taste in Insects.

F. Will* gives an account of many authors who have investi-
gated with more or less success the sense organs of various
Insects. He relates also the results of his own experiments,
and gives anatomical details of the sensory organs of the mouth
in various Hymenoptera.

Wasps, flying at liberty, were allowed to visit and taste a
packet of powdered sugar. This was left undisturbed for some
hours, and then replaced by alum of the same appearance. The
Wasps attacked the alum, but soon indicated by droll move-
ments that they perceived the difference. They put their
tongues in and out and cleansed them from the ill-tasted powder.
Two persisted at the alum till they rolled on the table in agony,
but they soon recovered and flew away. In a few hours the
packet was quite deserted. After a day's interval, during
which the sugar lay in its usual place, powdered, and of course
perfectly tasteless, dolomite was substituted. The wasps licked
it diligently and could not be persuaded for a long time that it
could do nothing for them. Similar experiments were made
with other substances, and Insects whose antennao and palps
had been removed were subjected to trial. The result clearly
proved that a sense of taste existed, and that its seat is in the
mouth.')' Peculiar nerve-endings, such as Meinert and Forel
had previously found in Ants, were found in abundance on the
labium, the paraglossae, and the inner side of the maxillae of
the Wasp. Some lay in pits, through the bases of which single
nerves emerged, and swelled into bulbs, or passed into peculiar
conical sheaths. Interspersed among the gustatory nerve-
endings were setae of various kinds, some protective, some tactile,
and others intended to act as guiding-hairs for the saliva.

* Zeits. f. wiss. Zool., 1885.

t "Will confirms, by his owu experiments (p. 685), Plateau's conclusion (Supra, p. 46),
that the maxillary and labial palps have nothing to do with the choice of food.

112 THE COCKROACH.

Will observes that the organs described satisfy the essential
conditions of a sense of taste. The nerve-endings pass free to
the surface, and are thus directly accessible to chemical stimulus.
Further, they are so placed that they and the particles of food
which get access to them are readily bathed by the saliva.
Moistened or dissolved in this fluid, the sapid properties of food
are most fully developed.

The sensory pits and bulbs appropriated to taste are believed
to be unusually abundant in the social Hymenoptera.

Sense of Hearing in Insects.

The auditory organs of Insects and other Arthropoda are re-
markable for the various parts of the body in which they occur.
Thus thev have been found in the first abdominal segment of

»/ tj

Locusts, and in the tibia of the fore-leg of Crickets and
Grasshoppers, and more questionable structures with peculiar
nerve-endings have been described as occurring in the hinder
part of the abdomen of various larvae (Ptij diopter a, Tabanus, Sec).
The auditory organ of Decapod Crustacea is lodged in the base
of the antennule, that of Stomapods in the tail, while an
auditory organ has been lately discovered on the underside of
the head of the Myriopod Scutigera.

Auditory organs are best developed in such Insects as
produce sounds as a call to each other. The Cockroach is
dumb, and it is, therefore, not a matter of surprise that no
structure which can be considered auditory should have ever
been detected in this Insect*

The sensory hairs of the skin have been already noticed
(p. 31).

*For a popular account of auditory organs in Insects, see Graber's Insekten,
Vol. I., page 287 ; also J. Midler, Vergl. Phys. d. Gesichssiun, p. 439 ; Siebold, Arch.
f. Naturg., 1844; Leydig, Midler's Arch. 1855 and 1860; Hensen, Zeits. f. wiss.
Zool., 1866; Graber, Denkschr. der Akad. der wiss. Wien, 1875; and Schmidt,
Arch. f. mikr. Anat. , 1875.

CHAPTER VII.

THE ALIMENTARY CANAL AND ITS APPENDAGES.

SPECIAL REFERENCES.

CHOLODKOWSKY. Zur Frage liber den Ban und liber die Innervation der Speichel-
driisen der Blattiden. Horce Soc. Eijtom. Rossica?, Torn. XVI. (1881). [Salivary
Glands of Cockroaches.]

SCHINDLER. Beitriige zur Kenntniss der Malpighi'schen Gefiisse der Insekten.
Zeits. f. wiss. Zool., Bd. XXX. (1878). [Malpighian Tubules of Insects.]

CHUN. Ueber den Bau, die Entwickelung, und physiologische Bedeutung der
Rectalclriisen bei den Insekten. Abh. der Senkenbergischen Naturforschers Gesell-
schaft, Bd. X. (1876). [Rectal Glands of Insects.]

LEYDIG. Lehrbuch der Histologie, &c., and VIALLANES. (Loc. cit. supra, chap, iv.)
[Histology of Alimentary Canal.]

BASCH. Untersuchungen iiber das Chylopoetische und Uropoetische System der
Blatta orientalis. I^ais. Akad. der AVissenschafteu. (Math — Nat. Classe.),
Bd. XXXIII. (1858). [Digestive and Excretory Organs of Blatta.]

SIRODOT. Recherches sur les Secretions chez les Insectes. Ann. Sci. Nat., 4" Serie,
Zool., Tom. X. (1859). [Digestive and Excretory Organs of Oryctes, &c.]

JOUSSET DE BELLESME. Recherches experimentales sur la digestion des Insectes
et en particulier de la Blatte (1875).

PLATEAU. Recherches sur les Phenomenes de la Digestion chez les Insectes. Mem.
de 1'Acad. Roy. de Belgique, Tom. XLI. (1874). [Now the principal authority on the
Digestion of Insects. The other physiological memoirs cited (Nos. 5, 6, 7) are chiefly
of historical interest. ]

PLATEAU. Note additionelle. Bull. Acad. Roy. de Belgique, 2e Ser., Tom. XLIV.
(1877). [Contains some corrections of importance.]

The Alimentary Canal

THE alimentary canal of the Cockroach measures about 2f
inches in length, and is therefore about 2| times the length of
the body. In herbivorous Insects the relative length of the
alimentary canal may be much greater than this ; it is five

t/ *

114

THE COCKROACH :

times the length of the body in Hydrophilus. Parts of the
canal are specialised for different digestive offices, and their
order and relative size are given in tho following: table : —

(Esophagus and crop

Grizzard

Chylific stomach

Small intestine

Colon

Rectum

•95 in.
•1

•5

•1

•875
•25

775

Fig. 56. — Alimentary Canal of Cockroach. X 2.

The principal appendages of the alimentary canal are the
salivary glands, the caeca! diverticula of the stomach, and the
Malpighian tubules.

THE ALIMENTARY CANAL AND ITS APPENDAGES. 115

Considered with respect to its mode of formation, the alimen-
tary canal of all but the very simplest animals falls into three
sections — viz., (1) the mesenteron, or primitive digestive cavity,
lined by hypoblast ; (2) the stomodseura, or mouth-section,
lined by epiblast, continuous with that of the external surface ;
and (3) the proctodacum, or anal section, lined by epiblast
folded inwards from the anus, just as the epiblast of the
stomodaoum is folded in from the mouth. The mesenteron of the
Cockroach is very short, as in other Arthropoda, and includes
only the chylific stomach with its diverticula. The mouth,
oesophagus, and crop form the stomodaeum, while the proc-
todaeum begins with the Malpighian tubules, and extends
thence to the anus. Both stomodaDum and proctodaeuin have
a chitinous lining, which is wanting in the mesenteron. At the
time of moult, or a little after, this lining is broken up and
passed out of the body.

The mouth of the Cockroach is enclosed between the labrum
in front, and the labium behind, while it is bounded laterally
by the mandibles and first pair of maxillae. The chitinous

Mo Ml

Fig. 57. — Section of "\Vall of Crop. Cc, chitinous layer ; C, chitinogenous cells ;
Mi, inner muscular layer ; Mo, outer do. X 275.

lining is thrown into many folds, some of which can be
obliterated by distension, while others are permanent and filled
with solid tissues. The lingua is such a permanent fold, lying
like a tongue upon the posterior wall of the cavity and reaching
as far as the external opening. The thin chitinous surface of
the lingua is hairy, like other parts of the mouth, and stiffened
bv special chitinous rods or bands. The salivary ducts open by
a common orifice on its hinder surface. Above, the mouth leads
into a narrow gullet or oesophagus, with longitudinally folded
walls, which traverses the nervous ring, and then passes
through the occipital foramen to the neck and thorax. Here it

116 THE COCKROACH:

gradually dilates into the long and capacious crop, whose large
rounded end occupies the fore-part of the abdomen. When
empty, or half-empty, the wall of the crop contracts, and is
thrown into longitudinal folds, which disappear on distension.
Numerous trachea! tubes ramify upon its outer surface, and
appear as fine white threads upon a greenish-grey ground.

Three layers can be distinguished in the wall of the crop-
viz., (1) the muscular, (2) the epithelial, and (3) the chitinous
layer.* The muscular layer consists of annular and longi-
tudinal fibres, crossing at right angles. (See fig. 58.) In most
animals the muscles of organic life, subservient to nutrition and
reproduction, are very largely composed of plain or unstriped
fibres. In Arthropoda (with the exception of the anomalous
Peripatus) this is not generally the case, and the muscular fibres
of the alimentary canal belong to the striped variety. The

**/•:, -;7V

Cc-

Fig. 58. — Wall of Crop, in successive layers. References as in fig. 57. X 250.

epithelium rests upon a thin structureless basement-membrane,
which is firmly united in the oesophagus and crop to the
muscular layer and the epithelium. The epithelium consists of
scattered nucleated cells, rounded or oval. These epithelial
cells, homologues of the chitinogenous cells of the integument,
secrete the transparent and structureless chitinous lining.
Hairs (seta)) of elongate, conical form, and often articulated at
the base, like the large setas of the outer skin, are abundant.

* Here, as generally in the digestive tube of the adult Cockroach, the peritoneal
layer is inconspicuous or wanting. It occasionally becomes visible — e.g., in the outer
wall of the Malpighian tubules, and in the tubular prolongation of the gizzard.

THE ALIMENTARY CANAL AXD ITS APPENDAGES.

117

In the oesophagus they are very long, and grouped in bundles
along sinuous transverse lines. In the crop the hairs become
shorter, and the sinuous lines run into a polygonal network.
The points of the hairs are directed backwards, and they no
doubt, serve to guide the flow of saliva towards the crop.

The gizzard has externally the form of a blunt cone, attached

by its base to the hinder end of the crop, and produced at the
other end into a narrow tube (J to J in. long), which projects
into the chylific stomach. Its muscular wall is thick, and
consists of ruanv layers of annular fibres, while the internal

•/ «/

cavity is nearly closed by radiating folds of the chitinous lining.
Six of the principal folds, the so-called " teeth," are much
stronger than the rest, and project so far inwards that they
nearly meet. They vary in form, but are generally triangular
in cross section and irregularly quadrilateral in side view.

Fig. 59. — Transverse section of Gizzard of Cockroach. The chitinous folds are
represented here as symmetrical. See next figure. X 30.

Between each pair are three much less prominent folds, and
between these again are slight risings of the chitinous lining.
A ridge runs along each side of the base of each principal tooth,
and the minor folds, as well as part of the principal teeth, are
covered with fine hairs. The central one of each set of
secondary folds is produced behind into a spoon-shaped process,
which extends considerably beyond the rest, and gradually
subsides till it hardly projects from the internal surface of the
gizzard. Behind each large tooth (i.e., towards the chvlific

C_7 CJ \ »/

118

THE COCKROACH

stomach) is a rounded cushion set closely with hairs, and
between and beyond these are hairy ridges. (See fig. 61.) The
whole forms an elaborate machine for squeezing and straining
the food, and recalls the gastric mill and pyloric strainer of the

Fig. 60. — The Six Primary Folds (teeth) of the Gizzard, seen in profile.

;'&-'' ,'fi' IV

l&w' /f -^Sf- '•

Fig. 61. — Part of Gi?zard laid open, showing two teeth (T) and the intermediate
folds, as well as the hairy pads below. A — A and B — B are lines of section
(see figs. 62 and 63). X 50.

Crayfish. The powerful annular muscles approximate the teeth
and folds, closing the passage, while small longitudinal muscles,
which can be traced from the chitinous teeth to the cushions,
appear to retract these last, and open a passage for the food.*

* Plateau has expressed a strong opinion that neither in the stomach of Crustacea
nor in the gizzard of Insects have the so-called teeth any masticatoiy character.
He compares them to the psalterium of a Ruminant, and considers them strainers
and not dividers of the food. His views, as stated by himself, will be fouud
on p. 131.

THE ALIMENTARY CANAL AND ITS APPENDAGES.

119

The gizzard ends below, as we have already mentioned, in a
narrow cylindrical tube which is protruded into the chylific
stomach for about one-third of an inch. Folds project from the
wall of this tube, and reduce its central cavity to an irregular
star-like figure. Below it ends in free processes slightly
different from each other in size and shape. The chitinous

ci tn

Fig. 62. — Section through one tooth and two intermediate spaces (see figure 61,
A — A). Cc, chitinous cuticle; C, chitinogenous layer; am, annular muscles;
p, peritoneal layer. X 75.

Fig. 63. — Section through one principal hairy ridge and two intermediate spaces
(see fig. 61, B — B) ; rm, radiating muscles ; tr, trachea. The other references
as before. X 75.

lining and the chitinogenous layer beneath pass to the end of
the tube and are then reflected upon its outer wall, ascending
till they meet the lining epithelium of the caecal tubes. Between
the wall of the gizzard-tube and its external reflected layer,
tracheal tubes, fat-cells, and longitudinal muscles are enclosed.

120

THE COCKROACH

Fig. 64. — Longitudinal section through Gizzard and fore-part of Chylific Stomach.
G, gizzard ; Tu, cpecal tube ; St, stomach ; Ep, its lining epithelium. A and B
are enlarged in the side figures. X 35.

A. — The Reflected Chitinogenous Layer of the Tubular Gizzard. Tr, tracheal
tube. X 400.

B. — One of the Tubular Extensions of the same, enclosing muscles and
tracheae. X 400.

THE ALIMENTARY CAXAL AXD ITS APPENDAGES.

121

The chylific stomach is a simple cylindrical tube, provided at
its anterior end with eight (sometimes fewer) csecal tubes, and
opening behind into the intestine. Its muscular coat consists of
a loose layer of longitudinal fibres, enclosing annular fibres.
Internal to these is a basement membrane, which supports an
epithelium consisting of elongate cells which are often clustered

Fig. 05. — Transverse section of tubular prolongation of Gizzard, within the Chylific
Stomach, part of which is shown at its proper distance. R C, reflected
chitinogenous layer ; Tr, tracheal tube ; M, cross section of muscle ; Ep,
epithelium of chylific stomach. X 100.

into regular eminences, and separated by deep cavities. The
epithelium forms no chitinous lining in the chylific stomach or
caacal tubes ; and this peculiarity, no doubt, promotes absorption
of soluble food in this part of the alimentary canal. Short
processes are given off from the free ends of the epithelial cells,
as in the intestines of many Mammalia and other animals.

122

THE COCKROACH :

Between the cells a reticulum is often to be seen, especially
where the cells have burst ; it extends between and among all
the elements of the mucous lining, and probably serves, like
the very similar structure met with in Mammalian intestines,*
to absorb and conduct some of the products of digestion.

Fig. 66.— Epithelium of Chylific Stomach. In the upper figure the digestive surface
is indented, while in the lower figure it is flat. Both arrangements are
common, and may be seen in a single section. The epithelial buds are shown
below, and again below these the annular and longitudinal muscles. X 220.

Different epithelial cells may be found in all the stages
noticed by Watney — viz., (1) with divided nuclei; (2) small,
newly produced cells at the base of the epithelium ; (3) short
and broad cells, overtopped by the older cells around ; (4) dome-
shaped masses of young cells, forming " epithelial buds";f
(5) full-grown cells, ranging with those on either side, so as to
form an unbroken and uniform series. The regeneration of the

* See Watney, Phil. Trans., 1877, Pt. II. The "epithelial buds" described and
figured in this memoir are also closely paralleled in the chylific stomach of the
Cockroach.

+ These epithelial buds have been described as glands, and we only saw their
significance after comparing them with Dr. Watney's account.

THE ALIMENTARY CANAL AXD ITS APPENDAGES.

123

tissue is thus provided for. The cells come to maturity and
burst, when new cells, the product of the epithelial buds, take
their place.

The epithelium of the chylific stomach is continued into the
eight cereal tubes, where it undergoes a slight modification of
form.

Fig. 67.— Section of Chylific Stomach, showing the six bundles of Malpighian

tubules. X 70.

At the hinder end of the chylific stomach is a very short

»•' •>

tube about half the diameter of the stomach, the small
intestine. At its junction with the chylific stomach are
attached, in six bundles, 60 or 70 long and fine tubules, the
Malpighian tubules.* The small intestine has the same general

* Development shows that these tubules belong to the proctodaeum, and not to the
mesenteron.

1 -24

THE COCKROACH I

structure as the oesophagus and crop ; its chitinous lining is
hairy, and thrown into longitudinal folds which become much
more prominent in the lower part of the tube. The junction of
the small intestine with the colon is abrupt, and a strong
annular fold assumes the character of a circular valve (fig. 68).
From the circular valve the colon extends for nearly an inch.
Its diameter is somewhat greater than that of the chylific
stomach, and uniform throughout, except for a lateral diverticu-
lum or ccecum, which is occasionally but not constantly present

Fig. 68. — Junction of Small Intestine with Colon. X 15.

towards its rectal end. The fore part of the colon is thrown
into a loose spiral coil. A constriction divides the colon from
the next division of the alimentary canal, the rectum.

The rectum is about J inch long, and is dilated in the middle
when distended. Six conspicuous longitudinal folds project
into the lumen of the tube. These folds are characterised by
an unusual development of the epithelium, which is altogether
wanting in the intermediate spaces, where the chitinous lining
blends with the basement-membrane, both being thrown into

THE ALIMENTARY CAXAL AXD ITS APPENDAGES.

125

sharp longitudinal corrugations. Between the six epithelial bands
and the muscular layer are as. many triangular spaces, in which
ramify tracheal tubes and fine nerves for the supply of the
epithelium. The chitinous layer is finely setose. The muscular
layer consists of annular fibres strengthened externally by
longitudinal fibres along the interspaces between the six
primary folds.*

Fig. 69. — Transverse section of Small Intestine and Colon, close to their

• junction. X 50.

The corrugated and non-epitheliated interspaces may be .
supposed to favour distension of the rectal chamber, while the
great size of the cells of the bands of epithelium is perhaps due
to their limited extent. Leydigf attributed to thes.e rectal
bands a respiratory function, and compared them to the
epithelial folds of the rectum of Libellulid larvae, which, as is
well known, respire by admitting fresh supplies of water into
this cavity. It is an obvious objection that Cockroaches and
other Insects in which the rectal bands are well developed do
not take water into the intestine at all. Gegenbaur has there-

;" The epithelial bands of the rectum of Insects were first discovered l>y
Swammerdam in the Bee (Bibl. Xat., p. 455, pi. xviii., fig. 1). Duf our called them
muscular bands (Rech. sur les Orthopteres, &c., p. 369, fig. 44).

t "Lehrbuch der Histologie," p. 337.

126

THE COCKROACH :

fore modified Leydig's hypothesis. He suggests (Grundziige
d. Vergl. Anat.) that the functional rectal folds of Dragon-flies
and the non-functional folds of terrestrial Insects are both
survivals of tracheal gills, which were the only primitive organs
of respiration of Insects. The late appearance of the rectal
folds and the much earlier appearance of spiracles is a serious
difficulty in the way of this view, as Chun has pointed out. It
seems more probable that the respiratory appendages of the
rectum of the Dragon-fly larva) are special adaptations to
aquatic conditions of a structure which originated in terrestrial
Insects, and had primarily nothing to do with respiration.

Fig. 70. — Transverse section of Rectum. X 50.

The number of the rectal bands (six) is worthy of remark.
We find six sets of folds in the gizzard and small intestine of
the Cockroach, six bundles of Malpighian tubules, with six
intermediate epitheliated bands. There are also six longitudinal
bands in the intestine of the Lobster and Crayfish. The
tendency to produce a six-banded stomodceum and proctodooum
may possibly be related to the six theoretical elements (two
tergal, two pleural, two sternal,) traceable in the Arthropod
exoskeleton, of which the proctodceum and stomod^eurn are
reflected folds.

THE ALIMENTARY CANAL AND ITS APPENDAGES.

127

The anus of the Cockroach opens beneath the tenth tergum,
and between two " podical ' plates. Anal glands, such as
occur in some Beetles, have not been discovered in Cockroaches.

Appendages. The Salivary Glands.

The three principal appendages of the alimentary canal of
the Cockroach are outgrowths of the three primary divisions of
the digestive tube ; the salivary glands are diverticula of the
stomodseum, the caecal tubes of the mesenteron, and the Mal-
pighian tubules of the proctodseurn.

Fig. 71. — Salivary Glands and Receptacle, right side. The arrow marks the opening
of the common duct on the back of the lingua. A, side view of lingua ; B, front

view of lingua.

A large salivary gland and reservoir lie on each side of the
oesophagus and crop. The gland is a thin foliaceous mass about
J in. long, and composed of numerous acini, which are grouped
into two principal lobes. The efferent ducts form a trunk,
which receives a branch from a small accessory lobe, and then

unites with its fellow. The common glandular duct thus

128 THE COCKROACH:

formed opens into the much larger common receptacular duct,
formed by the union of paired outlets from the salivary reser-
voirs. The common salivary duct opens beneath the lingua.
Each salivary reservoir is an oval sac with transparent walls,
and about half as long again as the gland. The ducts and
reservoirs have a chitinous lining, and the ducts exhibit a
transverse marking like that of a tracheal tube. When
examined with high powers the wall of the salivary gland
shows a network of protoplasm with large scattered nuclei,
resting upon a structureless chitinous membrane.

The salivary glands are unusually large in most Orthoptera.*
In other orders the}r are of variable occurrence and of very
unequal development.

The Ccecal Tubes.

There are eight (sometimes fewer) coecal tubes arranged in a
ring round the fore end of the chylific stomach; they vary in
length, the longer ones, which are about equal to the length of
the stomach itself, usually alternating with shorter ones, though
irregularities of arrangement are common. The tubes are
diverticula of the stomach and lined by a similar epithelium.
In the living animal they are sometimes filled with a whitish
granular fluid.

Similar csecal tubes, sometimes very numerous and densely
clustered, are attached to the stomach in many Crustacea and
Arachnida. The researches of Hoppe Seyler, Krukenberg,
Plateau, and others have established the digestive properties
of the fluid secreted in them, which agrees with the pancreatic
juice of Vertebrates.

The Malpicjhian Tubules.

The Malpighian tubules mark the beginning of the small
intestine, to which they properly belong. They are very
numerous (60-70) in the Cockroach, as in Locusts, Earwigs, and
Dragon-flies ; and unbranched, as in most Insects. Thev are

o •

about '8 inch in length, and '002 inch in transverse diameter,

so that they are barely visible to the naked eye as single

;; Except in Dragon-flies and Ephemerae.

THE ALIMENTARY CAXAL AXD ITS APPENDAGES. 129

threads. In larvse about one-fifth of an inch long, Schindler*
found only eight long tubules, the usual number in Thysanura,
Anoplura, and Termes; but the grouping into six masses, so
plainly seen in the adult, throws some doubt upon this observa-
tion. In the adult Cockroach the long threads wind about the
abdominal cavity and its contained viscera.

In the wall of a Malpighian tubule there may be dis-
tinguished (1) a connective tissue layer, with fine fibres and
nuclei ; within this, (2) a basement-membrane, between which

Fig. 72. — Malpighian Tubules of Cockroach. A , transverse section of young tubule ;
j), its connective-tissue or "peritoneal" layer; J5, older tubule, crowded with
urates ; 1r, tracheal tube ; C, tubule cut open longitudinally, showing three
states of the lining epithelium. X 200.

and the connective tissue layer runs a delicate, unbranched
tracheal tube ; (3) an epithelium of relatively large, nucleated
cells, in a single layer, nearly filling the tube, and leaving only
a narrow, irregular central canal. Transverse sections show
from four to ten of these cells at once. The tubules appear
transparent or yellow- white, according as they are empty or
full ; sometimes they are beaded or varicose ; in other cases, one
half is coloured and the other clear. The opaque contents
consist partly of crystals, which usually occur singly in the
epithelial cells, or heaped up in the central canal. Occasion-
all}7, they form spherical concretions with a radiate arrangement.
They contain uric acid, and probably consist of urate of soda.f

* Zeitsch. f. wiss. Zool., Bd. XXX.

t The contents of the Malpighian tubules may be examined by crushing the part
in a drop of dilute acetic acid, or in dilute sulphuric acid (10 per cent.). In the first
case a cover-slip is placed on the fluid, and the crystals, which consist of oblique
rhonibohedrons, or derived forms, are usually at once apparent. If sulphuric acid
is used, the fluid must be allowed to evaporate. In this case they are much more
elongated, and usually clustered. The murexide reaction does not give satisfactory
indications with the tubules of the Cockroach.

130 THE COCKROACH:

In the living Insect the tubules remove urates from the blood

which bathes the viscera ; the salts are condensed and crystal-
lised in the epithelial cells, by whose dehiscence they pass into
the central canals of the tubules, and thence into the intestine.
The Malpighian tubules develop as diverticula from the
proctodooum, which is an invagination of the outer integument
and its morphological equivalent. They are, therefore, similar
in origin to urinary organs opening upon the surface of the
body and developed as invaginations of the integument, like
the " shell-glands " of lower Crustacea, and the " green glands "
of Decapod Crustacea. The segmental organs of Peripattis,
Annelids, and Vertebrates do not appear to be possible equiva-
lents of the excretory organs of Arthropods. They arise, not
as involutions, but as solid masses of mesoblastic tissue, or as
channels constricted off from the peritoneal cavity, and their
ducts have only a secondary connection with the outside of the
body or with the alimentary canal.

Digestion of Insects.

The investigation of the digestive processes in Insects is
work of extreme difficulty, and it is not surprising that much
yet remains to be discovered. Plateau has, however, succeeded
in solving some of the more important questions, which, before
his time, had been dealt with in an incomplete or otherwise
unsatisfactory way. The experiments of Basch, though now
superseded by Plateau's more trustworthy results, deserve
notice as first attempts to investigate the properties of the
digestive fluids of Insects.

Basch set out with a conviction that where a chitinous lining
is present, the epithelium of the alimentary canal secretes chitin
only, and that proper digestive juices are only elaborated in
the chylific stomach, or in the salivary glands. The tests
applied by him seemed to show that the saliva, as well as the
contents of the oesophagus and crop, had an acid reaction, while
the contents of the chylific stomach were neutral at the begin-
ning of the tube and alkaline further down. From this he
concluded that the supposed deep-seated glands of the chylific
stomach secreted an alkaline fluid, which neutralised the acidity

THE ALIMENTARY CANAL AND ITS APPENDAGES. 131

of the saliva. Finding that the epithelial cells of the stomach
were often loaded with oil-drops, he concluded that absorption,
at least of fats, takes place here. The chylific stomach, care-
fully emptied of its contents, was found to convert starch into
sugar at ordinary temperatures. The saliva of the Cockroach
gave a similar result, and when a weak solution of hydrochloric
acid was added, Basch thought that the mixture could digest
blood-fibrin at ordinary temperatures.

Plateau's researches upon Periplaneta americana* modified by
subsequent experiments upon P. orientalist and by still more
recent observations, lead him to the following conclusion S+ : —

1. — The saliva of the Cockroach changes starch into glucose;
but the saliva is not acid, it is either neutral (P. orientalis) or
alkaline (P. americana). Any decided acidity found in the crop
is due to the ingestion of acid food ; but a very faint acidity
may occur, which results from the presence in the crop of a
fluid secreted by the caecal diverticula of the mesenteron.

2. — The glucose thus formed is absorbed in the crop, and no
more is formed in the succeeding parts of the digestive tube.

3. — The function of the gizzard is that of a grating or
strainer. It has no power of trituration. If the animal con-
sumes vegetable food rich in cellulose, a substance not' capable
of digestion in the crop, the fragments are found ' unaltered as
to form and size in the mesenteron. If it is supplied with
plenty of farinaceous food, such as meal or flour, the saliva is
not adequate to the complete solution and transformation of the
starch, and the intestine is found full of uninjured starch
granules, which must have traversed the gizzard without

<*. / * O

crushing.

4. — The coecal diverticula secrete a feebly acid fluid. To
demonstrate its acidity an extremely sensitive litmus solution,
capable of indicating one part in twenty thousand of hydro-
chloric acid, must be used. The fluid secreted by the caeca
emulsifies fats, and converts albuminoids into peptones.

In all Insects digestion is effected in the following way
(which is particularly easy of demonstration in Carabus and

* Bull. Acad. Eoy. de Belgique, 1876.
t Ib.,1877.

+ We are indebted to Prof. Plateau for the statement of his views given in the
text.

132 THE COCKROACH.

Dytiscus). The crop is filled with food coarsely divided by the
mandibles, and the gizzard being shut to prevent further
passage, the fluid secretion of the cceca ascends to the crop, and
there acts upon the food. Digestion is effected in the crop, and
not beyond it. This is clear beyond doubt. In Decapod Crus-
tacea also it is very easy to prove that the fluid secreted by the
so-called liver ascends into the stomach (which corresponds to
the crop, together with the gizzard of the Insect). To satisfy
ourselves on this point we have only to open a Crayfish during
active digestion.

When digestion in the crop is finished, the gizzard relaxes,
and the contents of the crop, now in a semi-fluid condition,
pass into the mesenteron, which is devoid of chitinous lining,
and particularly fitted for absorption.

5. --There are no absorbent vessels properly so called, and
Plateau has long thought that the products of digestion pass by
osmosis directly through the walls of the digestive tube, to mix
with the blood in the perivisceral space. If we may rely upon
what is now known of the process in Vertebrates, we should be
led to modify this explanation. It is very likely that in Insects,
as in Vertebrates, absorption is effected by the protoplasm of
the epithelial cells, which select and appropriate certain sub-
tances formed out of the dissolved food. Not only do the
epithelial cells transmit to the neighbouring blood-currents the
materials which they have previously absorbed, but they subject
certain kinds to further elaboration. The protoplasm of the
epithelial cells of Vertebrates is capable of forming fat. Tims,
a mixture of soap and glycerine, injected into the intestine of
a Vertebrate, is absorbed by the lacteals in the form of oil-
drops. Modern physiologists allow, too, that part of the
peptone is similarly changed into albumen, without transport to
a distance, by the activity of the epithelial lining.

These facts explain why Plateau was unable to isolate the
secretion of the epithelium of the chylific stomach of Insects.
The cells are not secretory, but absorbent ; and the secretion
vainly sought for does not actually exist.

CHAPTER VIII.
THE ORGANS OF CIRCULATION AND RESPIRATION.

SPECIAL REFERENCES.

VERLOREN. Mem. sur la Circulation dans les Insectes. Mem. cour. par TAcad.
Roy. de Belgique, Tom. XIX. (1847). [Structure of Circulatory Organs in a number
of different Insects.]

GRABER. Ueb. den Propulsatorischen Apparat der Insekten. Arch. f. rnikr.
Anat., Bd. IX. (1872). [Heart and Pericardium.]

LEYDIG. Larve von Corethra plumicornis. Zeits. f. wiss. Zool., Bd. III. (1852).
[Valves in Heart.]

LAXDOIS, H. Beob. iib. das Blut der Insekten. Zeits. f. wiss. Zool., Bd. XIV.
(1864). [Blood of Insects.]

JAWOBOWSKI. Entw. des Riickengefiisses, &c., bei Chironomus. Sitzb. der k.
Akad. der Wiss. "NVien., Bd. LXXX. (1879). [Minute Structure and Development
of Heart.]

LANDOIS, H. , and THELEX. Der Tracheenverscliluss bei den Insekten. Zeits. f.
wiss. Zool., Bd. XVII. (1867). [Stigmata.]

PALMEN. Zur Morphologic des Tracheensystems (1877). [Morphology of Stigmata
and Tracheal Gills.]

MACLEOD. La Structure des Tracheesetla Circulation Peritrachcenne. (Brussels,
1880.)

LUBBOCK. Distribution of Tracheae in Insects. Trans. Linn. Soc. , Vol. XXIII.
(1860).

RATHKE. Untersuch. iib. den Athmungsprozess der Insekten. Schr. d. Phys. Oek.
Gesellsch. zu Kiinigsberg. Jahrg. I. (1861). [Experiments and Observations on
Insect-respiration.]

PLATEAU. Rech. Experimentales sur les Mouvements Respiratoires des Insectes.
Mem. de 1'Acad. Roy. de Belgique, Tom. XLV. (1884). Preliminary notice in Bull.
Acad. Roy. de Belgique, 1882.

LANGEXDORFF. Studien iib. die Innervation der Athembewegungen. — Das
Athmungscentrum der Insekten. Arch. f. Anat. u. Phys. (1883). [Respiratory
Centres of Insects.]

Circulation of Insects.

A VERY long chapter might be written upon the views advanced
by different writers as to the circulation of Insects. Malpighi
first discovered the heart or dorsal vessel in the young Silk-

«/ o

worm. His account is tolerably full and remarkably free from
mistakes. The heart of the Silkworm, he tells us, extends the
whole length of the body, and its pulsations are externally
visible in young la^73e. He supposed that contraction is effected

134 THE COCKROACH:

by muscular fibres, but these he could not distinctly see. The
tube, he says, has no single large chamber, but is formed of
many little hearts (corcula) leading one into another. The
number of these he could not certainly make out, but
believed that there was one to each segment of the body.
During contraction each chamber became more rounded, and
when contraction was specially energetic, the sides of the tube
appeared to meet at the constrictions. The flow of blood, he
ascertained, was forward, the rhythm not constant. No arteries
were seen to be given off from the heart* Swammerdam
thought that his injections ascertained the existence of vessels
branching out from the heart, f but this proved to be a mistake.
Lyonnet added many details of interest to what was previously
known. He came to the conclusion that there was no system
of vessels connected with the heart, and even doubted whether
the organ so named was in effect a heart at all. Marcel de
Serres maintained that it was merely the secreting organ of the
fat-body. Cuvier and Dufour doubted whether any circulation,
except of air, existed in Insects. This was the extreme point of
scepticism, and naturalists were drawn back from it by Herold,J
who repeated and confirmed the views held by the seventeenth-
century anatomists, and insisted upon the demonstrable fact
that the dorsal vessel of an Insect does actually pulsate and
impel a current of fluid. Carus, in 1826, saw the blood flowing
in definite channels in the wings, antennae, and legs. Straus-
Durckheim followed up this discovery by demonstrating the con-
tractile and valvular structures of the dorsal vessel. Blanchard
affirmed that a complex system of vessels accompanied the air
tubes throughout the body, occupying peritracheal spaces sup-
posed to exist between the inner and outer walls of the tracheae.
This peritracheal circulation has not withstood critical inquiry, §
and it might be pronounced wholly imaginary, except for the
fact that air tubes and nerves are found here and there within
the veins of the wings of Insects.

* Dissert, de Bornbyce, pp. 15, 1C (1660).

f Biblia Nature, p. 410.

J Schrift. d. Marburg. Naturf. Gesellschaft, 1823.

§ See, for a full account of this discussion, MacLeod sur la Structure des
Trachees, et la Circulation Peritracheenne (1880). The peritracheal circulation was
refuted by Joly (Ann. Sci. Nat., 1849).

THE ORGANS OF CIRCULATION AND RESPIRATION.

135

Fig. 73.— Heart, Alary Muscles, and Tracheal Arches, seen from below ; to the left
is a side view of the heart. T- , T3, A ] , alary muscles attached to the second
thoracic, third thoracic, and first abdominal terga. X G. Fig. 35 (p. 74) is
not quite correct as to the details of the heart. The thoracic portion should be
chambered, and additional chambers and alary muscles represented at the end
of the abdomen. These omissions are rectified in the present figure.

136 THE COCKROACH :

Heart of tlie Cockroach.

The heart of the Cockroach is a long, narrow tube, lying
immediately beneath the middle line of the thorax and abdomen.
It consists of thirteen segments (fig. 73), which correspond to
three thoracic and ten abdominal somites. Each segment,
as a rule, ends behind in a conspicuous fold which projects
backwards from the dorsal surface ; immediately in front of
this are two lateral lobes. The median lobe passes into the
angle between two adjacent terga, and is continuous with the
dorsal wall of the segment next behind, from which it is
separated only by a deep constriction, while the lateral folds

AIL

Fig. 74. — Diagram to show the interventricular valves and lateral inlets of the
Heart. ML, median lobe ; V, valve ; /, lateral inlet.

conceal paired lateral inlets,* which lead from the pericardial
space to the hinder end of each chamber of the heart. Imme-
diately in front of each constriction is the interventricular valve,
a pear-shaped mass of nucleated cells, hanging down from the
upper wall of the heart, and inclining forward below. The
position of this valve indicates that during systole it closes upon
the constricted boundary between two chambers, thus shutting
off at once the inlets and the passage into the chambers behind.
In this way the progressive and rhythmical contraction of the
chambers impels a steady forward current of blood, allowing an

* It may be observed that Graber, who has paid close attention to the heart of
Insects, describes the inlets (c. y., in Dytiscus) as situated, not at the hinder end, but
in the middle of each segment. We have not been able to discover such an arrange-
ment in the heart of the Cockroach.

THE ORGANS OF CIRCULATION AND RESPIRATION.

137

intermittent stream to enter from the pericardial space, but
preventing regurgitation.

The wall of the heart includes several distinct layers. There
are (1) a transparent, structureless intima, only visible when
thrown into folds ; (2) a partial endocardium, of scattered,
nucleated cells, which passes into the interventricular valves ;
(3) a muscular layer, consisting of close-set annular, and distant
longitudinal fibres. The annular muscles are slightly inter-
rupted at regular and frequent intervals, and are imperfectly

Fig. 75. — Junction of two chambers of the Heart, seen from above. ML, median

lobe ; /, lateral inlet.

joined along the middle line above and below, so as to indicate
(what has been independently proved) that the heart arises as two
half-tubes, which afterwards join along the middle. Elongate
nuclei are to be seen here and there among the muscles. The
adventitia (4), or connective tissue layer, is but slightly developed
in the adult Cockroach.

Within the muscular layer is a structure which we have
failed to make out to our own satisfaction. It presents the
appearance of regular but imperfect rings, which do not extend
over the upper third of the heart. They probably meet in a
ventral suture, but this and other details are hard to make out,
owing to the transparency of the parts. The rings stain with

138 THE COCKROACH:

difficulty, and we have not observed nuclei belonging to them.
Each extends over more than one bundle of annular muscles.

The difficulty of investigating a structure so minute and
delicate as the heart of an Insect may explain a good deal of the
discrepancy noted on comparing various published descriptions.
Perhaps the most obvious peculiarity which distinguishes the
heart of the Cockroach, is the subdivision of the thoracic por-
tions into three chambers, which, though less prominent in side-
view than the abdominal chambers, are, nevertheless, perfectly
distinct. The number of abdominal chambers is also unusually
high ; but it is so easy to overlook the small chambers at the
posterior end of the abdomen, that the number given in some
of the species may have been under-estimated.

Pericardial Diaphragm and Space.

The heart lies in a pericardial chamber, which is bounded
above by the terga and the longitudinal tergal muscles ; below
by a fenestrated membrane, the pericardial diaphragm. The
intermediate space, which is of inconsiderable depth, is nearly
filled by a cellular mass laden with fat, and resembling the
fat-body.

The pericardial diaphragm, or floor of the pericardium, is
continuous, except for small oval openings scattered over its
surface. It consists of loosely interwoven fibres, interspersed
with elongate nuclei (connective-tissue corpuscles) and con-
nected by a transparent membrane. Into the diaphragm are
inserted pairs of muscles, which, from their shape and supposed
continuity with the heart, have been named alee cordis, or alary
muscles.* These are bundles of striated muscle,, about '003 in.
wide, which arise from the anterior margin of each tergum.
In the middle of the abdomen every alary muscle passes
inwards for about *04 in., without breaking-up or widening,
and then spreads out fanwise upon the diaphragm. The
fibres unite below the heart with those of the fellow-muscle, and
also join, close to the heart, those of the muscles in front and
behind. The alary muscles are often said to distend the heart
rhythmically by drawing its walls apart, but this cannot be

* Ly on net.

THE ORGANS OF CIRCULATION AND RESPIRATION.

139

true. They do not pass into the heart at all. Even if they did,
a pull from opposite sides upon a flexible, cylindrical tube,
would narrow and not expand its cavity. Moreover, direct
observation* shows that the heart continues to beat after all the
alary muscles have been divided, and even after it has been cut
in pieces. These facts suggest that the heart of Insects is in-
nervated by ganglia upon or within it, and indeed transparent
larva), such as Corethra or Chironomus, exhibit paired cells,
very like simple ganglia, along the sides of the heart.

Fig. 76. — Heart and Pericardial Diaphragm. On the right, as seen from above ; on
the left, as seen from below ; the bottom figure represents a transverse section.
Ht, heart ; PD, pericardial diaphragm ; A M, alary muscle ; Tr, trachea! tube ;
PC, pericardia! fat-cells ; PC1, niultinucleate fat-cells.

Scattered over the upper surface of the pericardial diaphragm
are groups of cells, similar to the fat-masses of the perivisceral
space. Over the fan-like expansions of the alary muscles are

* Brandt, Ueb. d. Herz cler Insekten u. Muscheln. Mel. BioL Bull. Acad. St.
Petersb. Tom. YI. (1866).

140 THE COCKROACH :

different fat-cells, which form branched and raultinucleate lobes,
and radiate in the same direction as the underlying muscles.

Tracheal trunks, arising close to the stigmata, ascend upon
the tergal wall towards the heart. They overlie the alary
muscles, and end near the heart by bifurcation, sending one
branch forward and another backward to meet corresponding
branches of adjacent trunks. A series of arches is thus formed
bv the dorsal trachea) on each side of the heart. Occasionally

»/ ••

an arch is subdivided into two smaller parallel tubes. A few
branches of distribution are given off to the fat-cells of the
pericardium.

Graber has explained the action of the pericardial diaphragm
and chamber in the following way.* When the alary muscles
contract, they depress the diaphragm, which is arched upwards
when at rest. A rush of blood towards the heart is thereby set
up, and the blood streams through the perforated diaphragm
into the pericardial chamber. Here it bathes a spongy or
cavernous tissue (the fat-cells), which is largely supplied with
air tubes, and having been thus aerated, passes immediately
forwards to the heart, entering it at the moment of diastole,
which is simultaneous with the sinking of the diaphragm.

In the Cockroach the facts of structure do not altogether
justify this explanation. The fenestnc of the diaphragm are
mere openings without valves. The descent of a perforated non-
valvular plate can bring no pressure to bear upon the blood,
for it is not contended that the alary muscles are powerful
enough to change the figure of the abdominal rings. Moreover,
we find comparatively few tracheal tubes in the pericardial
chamber, and can discover no proof that in the Cockroach
the fat-cells adjacent to the heart have any special respi-
ratory character. The diaphragm appears to give mechanical
support to the heart, resisting pressure from a distended ali-
mentary canal, while the sheets of fat-cells, in addition to their
proper physiological office, may equalise small local pressures,
and prevent displacement. The movement of the blood towards
the heart must (we think) depend, not upon the alary muscles,
but upon the far more powerful muscles of the abdominal wall,
and upon the pumping action of the heart itself.

* Arch. f. mikr. Anat., Bd. IX. (1872) ; Insekten, ch. x.

THE ORGANS OF CIRCULATION AND RESPIRATION. 141

Circulation of the Cockroach.

The pulsations of the heart are rhythmical and usually
frequent, the number of beats in a given time varying with the
species, the age, and especially with the degree of activity or
excitement of the Insect observed.*

Cornelius •(• watched the pulsations in a white Cockroach
immediately after its change of skin, and reckoned them at
eighty per minute ; but he remarks that the Insect was restless,
and that the beats were probably accelerated in consequence.

In the living Insect a wave of contraction passes rapidly
along the heart from behind forwards ; and the blood may
under favourable circumstances be seen to flow in a steady,
backward stream along the pericardial sinus, to enter the lateral
aperture of the heart. The peristaltic movement of the dorsal
vessel may often be observed to set in at the hinder end of the
tube before the preceding wave has reached the aorta.

From the heart a slender tube (the aorta) passes forward to
the head. It lies upon the dorsal surface of the oesophagus,
which it accompanies as far as the supra-oesophageal ganglia.
In many Insects the thoracic portion of the dorsal vessel is
greatly narrowed and non-valvular, forming the aorta of most
writers on Insect Anatomy. The aorta often dips downward
near its origin, but in the Cockroach the thoracic portion of the
vessel keeps nearly the same level as the abdominal. It gives
off no lateral branches, but suddenly ends immediately in front
of the cesophageal ring in a trumpet-shaped orifice, f by which
the blood passes at once into a lacunar system which occupies
the perivisceral space. Here the blood bathes the digestive and
reproductive organs, receives the products of digestion, which
are not transmitted by lacteals, but discharged at once into the
blood ; here, too, it gives up its urates to the excretory tubules,
and its superfluous fats to the finely-divided lobules of the fat-
body. The form of the various appendages of the alimentary

* Newport, in Todcl's Cyclopaedia of Anatomy and Physiology, Art. Insecta,
pp. 981-2.

T Beitr. zur niiheren Kenntniss von Periplaneta orientalis, p. 19.

J The termination of the aorta has been described by Newport, in Sphinx (Phil.
Trans., 1832, Pt. I.,p. 385) Vanessa, Meloe, Bla})$ and Timarcha. (Todd's Cycl.,
Art. "Insecta," p. 978.)

142 THE COCKROACH:

canal (salivary glands, cnccal tubes, and Malpighian tubules), as
well as of the testes, ovaries, and fat-body, is immediately con-
nected with the passive behaviour of the fluid upon which their
nutrition depends. Instead of being compact organs injected
at every pulsation by blood under pressure, they are diffuse,
tubular, or branched, so as to expose as large a surface as
possible to the sluggish stream in which they float.

From the perivisceral space the blood enters the pericardial
sinus by the apertures in its floor, and returns thence by the
lateral inlets into the heart.

No satisfactory injections of the circulatory channels can be
made in Insects, on account of the large lacunae, or cavities
without proper wall, which are interposed between the heart
and the extremities of the body. In the wings and other
transparent organs the blood has been seen to flow along
definite channels, which form a network, and resemble true
blood vessels in their arrangement. Whether they possess a
proper wall has not been ascertained. It is observed that in
such cases the course of the blood is generally forwards along
the anterior, and backwards along the posterior, side of the
appendage. The direction of the current is not, however, quite
constant, and the same cross branch may at different times
transmit blood in different directions.*

Blood of the Cockroach.

The blood of the Cockroach may be collected for examination
by cutting off one of the legs, and wiping the cut end with a
cover- slip. It abounds in large corpuscles, each of which
consists of a rounded nucleus invested by protoplasm. Amoeboid
movements may often be observed, and dividing corpuscles are
occasionally seen. Crystals may be obtained by evaporating a
drop of the blood without pressure ; they form radiating
clusters of pointed needles. The fresh-drawn blood is slightly
alkaline ; it is colourless in the Cockroach, but milky, greenish,
or reddish in some other Insects. The quantity varies greatly,
according to the nutrition of the individual : after a few days'
starvation, nearly all the blood is absorbed. Larvae contain much
more blood, in proportion to their weight, than other Insects.

* Moseley, Q. J. Micr. Sci. (1871).

THE ORGANS OF CIRCULATION AND RESPIRATION. 143

Respiratory Organs of Insects.

The respiratory organs of Insects consist of ramified trachea!
tubes, which communicate with the external air by stigmata or

•J CJ

spiracles. Of these spiracles the Cockroach has ten pairs —
eis:ht in the abdomen and two in the thorax. The first

thoracic spiracle lies in front of the rnesothorax, beneath the
edge of the tergum ; the second is similarly placed in front of
the metathorax. The eight abdominal spiracles belong to the
first eight somites ; each lies in the fore part of its segment,
and hence, apparently, in the interspace between two terga and
two sterna. The first abdominal spiracle is distinctly dorsal
in position.

The disposition of the spiracles observed in the Cockroach
is common in Insects, and, of all the recorded arrangements,
this approaches nearest to the plan of the primitive respiratory
system of Tracheata, in which there may be supposed to be
as many spiracles as somites.* The head never carries spiracles
except in Smynthurm, one of the Collembola (Lubbock). Many
larvae possess only the first of the three possible thoracic
spiracles ; in perfect Insects this is rarely or never met with
(Pulicidce?), but either the second, or both the second and
third, are commonly developed. Of the abdominal somites,
only the first eight ever bear spiracles, and these may be
reduced in burrowing or aquatic larvae to one pair (the eighth),
while all disappear in the aquatic larva of Ephemera.

From the spiracles, short, wide air- tubes pass inwards, and
break up into branches, which supply the walls of the bod}r
arid all the viscera. Dorsal branches ascend towards the heart
on the upper side of the alary muscles ; each bifurcates
above, and its divisions join those of the preceding and suc-
ceeding segments, thus forming loops or arches. The principal
ventral branches take a transverse direction, and are usually
connected by large longitudinal trunks, which pass along the

: The oldest Tracheate actually known to bear spiracles is the Silurian Scorpion
of Gothland and Scotland (Scudder, in Zittel's PaL-eontologie, p. 738). We need
not say that this is very far removed from the primitive Tracheate which morpho-
logical theory requires. The existing Peripatus makes a nearer approach to the
ideal ancestor of all Tracheates, if we suppose that all Tracheates had a common
ancestor of any kind, which is not as yet beyond doubt.

144

THE COCKROACH :

sides of the body; the Cockroach, in addition to these, possesses
smaller longitudinal vessels, which lie close to the middle line,
on either side of the nerve-cord.* The ultimate branches form
an intricate network of extremely delicate tubes, which pene-
trates or overlies every tissue.

Fig. 77.— Tracheal System of Cockroach. Side view of head seen from without,
introducing the chief branches of the left half. X 15.

* The longitudinal air-tubes are characteristic of the more specialised Tracheata.
In Araneidre, many Julidre, and Peripatus each spiracle has a separate t radical
system of its own.

THE ORGANS OF CIRCULATION AND RESPIRATION.

145

Fig. 78. — Tracheal System of Cockroach. Top and front of head seen from

without, x 15.

Fig. 79.— Tracheal System of Cockroach. Back of head, seen from the front, the
fore half being removed. X 15. The letters A— J indicate corresponding
branches in figs. 77, 78, and 79.

146

THE COCKROACH :

Fig. 80. — Trachea! System of Cockroach. The dorsal integiiment removed and the

viscera in place. X 5.

THE ORGANS OF CIRCULATION AND RESPIRATION. 147

Fig. 81. — Tracheal System of Cockroach. The viscera removed to show the ventral

tracheal communications, x 5.

148

THE COCKROACH :

Fig. 82.— Tracheal System of Cockroach. The ventral integument and viscera
removed to show the dorsal tracheal communications. X 5.

THE ORGANS OF CIRCULATION AND RESPIRATION.

149

Tracheal Tubes.

The accompanying figures sufficiently explain the chief
features of the tracheal system of the Cockroach, so far as it
can be explored by simple dissection. Leaving them to tell
their own tale, we shall pass on to the minute structure
of the air- tubes, the spiracles, and the physiology of Insect
respiration.

The tracheal wall is a folding-in of the integument, and
agrees with it in general structure. Its inner lining, the

O O O '

intima, is chitinous, and continuous with the outer cuticle. It
is secreted by an epithelium of nucleated, chitinogenous cells,
and outside this is a thin and homogeneous basement mem-
brane. The integument, the tracheal wall, and the inner
layers of nearly the whole alimentary canal are continuous
and equivalent structures. The lining of the larger tracheal
tubes at least is shed at every moult, like that of the stomodseum
and proctodoeum.

Fig. 83. —Tracheal tube with its epithelium and spiral thread. Slightly altered
from a figure given by Chun (Rectal-driisen bei den Insekten, pi. iv., fig. 1).

150 THE COCKROACH:

Tracked Thread.

In the finest tracheal tubes ('0001 in. and under) the intima
is to all appearance homogeneous. In wider tubes it is
strengthened by a spiral thread, which is denser, more refrac-
tive, and more flexible than the intervening membrane. The
thread projects slightly into the lumen of the tube, and is often
branched. It is interrupted frequently, each length making
but a few turns round the tube, and ending in a point. The
thread of a branch is never continued into a main trunk. Both
the thread and the intervening membrane become invisible or
faint when the tissue is soaked with a transparent fluid, so as

Fig. 84. — Intirna (chitinous lining) of a large tracheal tube. The spiral thread
divides here and there. Copied from MacLeod, loc. cit., fig. 9.

to expel the air. Both, but especially the thread, absorb
colouring matter with difficulty. The thread, from its greater
thickness, offers a longer resistance to solvents, such as caustic
alkalies, and also to mechanical force ; it can therefore be
readily unrolled, and often projects as a loose spiral from the
end of a torn tube, while the membrane breaks up or crumbles
away.*

The large tracheal tubes close to the spiracles are without
spiral thread, and the intima is here subdivided into polygonal

* Investigators are not yet agreed as to the minute structure of the tracheal
thread. Chun (Abh. d. Senkenberg. Naturf. Gesells., Bd. X., 1876) considers it an
independent chitinous formation, not a mere thickening of the intima. He describes
the thread as solid. The intima itself is, he believes, divisible in the larger tubes
iuto an inner and an outer layer, into both of which the thread is sunk. Macloskie
(Amer. Nat., June, 1884) describes the spiral as a fine tubule, opening by a fissure
along its length. He regards it as a hollow crenulation of the intima, and con-
tinuous therewith. Packard (Amer. Nat. Mag., May, 1886) endeavours to show that
the thread is not spiral, but consists of parallel thickenings of the intima. He is
unable to find proof of the tubular structure, or of the external fissure. We
have specially examined the trachea of the Cockroach, and find that the thread can
readily be unwound for several turns. It is truly spiral.

THE ORGANS OF CIRCULATION AND RESPIRATION. 151

areas, each of which is occupied by a reticulation of very fine
threads. This structure may be traced for a short distance
between the turns of the spiral thread.

The chitinogenous layer of the tracheal tubes is single, and
consists of polygonal, nucleated cells, forming a mosaic pattern,
but becoming irregular and even branched in the finest
branches. The cell walls are hardly to be made out without
staining. Externally, the chitinogenous cells rest upon a
delicate basement membrane.

Where a number of branches are given off together, the
tracheal tube may be dilated. Fine branches, such as accom-
pany nerves, are often sinuous. In the very finest branches
the tube loses its thread, the chitinogenous cells become
irregular, and the intima is lost in the nucleated protoplasmic
mass which replaces the regular epithelium of the wider
tubes.*

The Spiracles.

The spiracles of the Cockroach are by no means of compli-
cated structure, but their small size, and the differences between
one spiracle and another, are difficulties which cost some pains
to overcome.

The first thoracic spiracle (fig. 85) is the largest in the body.
It lies in front of the mesothorax, between the bases of the first
and second legs. It is placed obliquely, the slit being inclined
downwards and backwards, and is closed externally by a large,
slightly two-lobed valve, attached by its lower border. The
aperture immediately within the valve divides into two nearly
equal cavities, each of which leads to a separate tracheal trunk ;
and between these cavities is a septum, thickened on its free
edge, against which the margin of the valve appears to close.
A special occlusor muscle arises from the integument below the
spiracle, and is inserted into a chitinous process which projects
inwardly from the centre of the valve. A second muscle, whose
connections and mode of action we have not been able to make
out satisfactorily, lies beneath the first, and is inserted into the
thickened edge of the septum.

* It has been supposed that these irregular cells of the tracheal endings pass into
those of the fat-body, but the latter can always be distinguished by their larger and
more spherical nuclei.

152

THE COCKROACH :

The second thoracic spiracle (fig. 8G) lies in front of the meta-
thorax, between the bases of the second and third legs. It is
much smaller and simpler than the first. Its valve is nearly
semi- circular, and the free border is strengthened on its deep
surface by a chitinous rim, which terminates beyond the end of
the hinge of the valve in a process which gives insertion to the
occlusor muscle.

Fig. 85.— First Thoracic Spiracle (left side), seen from the outside. X 70. V, valve ;
/, setose lining of valve (mouth of tracheal tube) X 230. The occlusor muscle is
shown. The arrow indicates the direction of air entering the spiracle. In the
natural position this spiracle is set obliquely, the slit being inclined downwards
and backwards. (P. americana.}

The abdominal spiracles present quite a different plan of
structure. The external orifice is permanently open, owing to
the absence of valves, but communication with the tracheal trunk
may be cut off at pleasure by an internal occluding apparatus.
The external orifice leads into a shallow oval cup, which commu-
nicates with the tracheal trunk by a narrow slit, or internal
aperture of the spiracle. The chitinous cuticle, surrounding
this internal aperture, is richly provided with setae, which are
turned towards the opening.* Fig. 87 C represents a spiracle

* In the first abdominal spiracle the sette are developed only on that lip which
carries the bow.

THE ORGANS OF CIRCULATION AND RESPIRATION.

153

seen from within, and shows that the slit divides the cup into
two unequal lips, the smaller of which inclines away from the
middle line of the body, is movable, and is strengthened on its
deep surface by a curved chitinous rod, the "bow' of Landois.

Fig. 80. — Second Thoracic Spiracle (left side), seen from the outside. X 70. V, lower
(movable) valve. The occlusor muscle is shown. The arrow indicates the
direction of air entering the spiracle. (P. americana.)

From the opposite lip, a pouch is thrown out, which serves for
the attachment of the occlusor muscle. The muscle is inserted
into the extremity of the bow, and when it contracts, the bow is
pulled over into the position shown in fig. S7D, and the opening
is closed. The antagonist muscle, which exists in all the
abdominal spiracles, is shown in fig. 88 ; it arises from the

154

THE COCKROACH I

supporting plate of the spiracle, and is inserted opposite to the
occlusor, into the extremity of the bow.

Fig. 37, — Four views of the First Abdominal Spiracle (left side). X 70. The bow

is shaded in all the figures. (P. americana.)

A — The spiracle, seen from the outside ; p, lateral pouch ; /, internal aperture.

B— Do., side view.

C— Do., seen from the inside, the aperture open. The occlusor muscle

is shown.
D — The spiracle, seen from the inside, the aperture shut.

THE ORGANS OF CIRCULATION AND RESPIRATION.

155

Each of the eight abdominal spiracles is constructed on this
plan ; the first merely differs from the others in its larger size
and dorsal position, being carried upon the lateral margin of
the first abdominal tergum, whereas the others are placed on
the side of the body, each occupying an interspace between two

Fig. 88. — Abdominal Spiracle (left side) in side view, showing the bow : X 70 ;
p, lateral pouch of spiracle, seen from within. The tesselated structure of
the spiracle and trachea is shown at A (X 230), and the margin of the external
aperture at B (x 230). (P. americana.)

terga and two sterna. The bow is of about the same length in
all ; hence the apparent disproportion in the figures of different
spiracles. The external aperture of the abdominal spiracles
is oval or elliptical, placed vertically and directed backwards.
We have already pointed out that the wall of the air-tube,
for a short distance from the spiracular orifice, has a tesselated
instead of a spiral marking. In the thoracic spiracles the
tesselated cells are grouped round regularly placed setae
(fig. 85 /). The chitinous cuticle within the opening is crowded
with fine setae, which are often arranged so as to form a fringe
on one or both sides of the internal aperture. (Supra, p. 152.)

156 THE COCKROACH :

Mechanism of Respiration.

In animals with a complete circulation, aerated blood is dif-
fused throughout the body by means of arteries and capillaries,
which deliver it under pressure at all points. Such animals
usually possess a special aerating chamber (lung or gill), where
oxygen is made to combine with the haemoglobin of the blood.
It is otherwise with Insects. Their blood escapes into great
lacunre, where it stagnates, or flows and ebbs sluggishly, and
a diffuse form of the internal organs becomes necessary for
their free exposure to the nutritive fluid. The blood is not
injected into the tissues, but they are bathed by it, and the
compact kidney or salivary gland is represented in Insects by
tubules, or a thin sheet of finely divided lobules. By a
separate mechanism, air is carried along ramified passages to
all the tissues. Every organ is its own lung.

We must now consider in more detail how air is made to
enter and leave the body of an Insect. The spiracles and the
air-tubes have been described, but these are not furnished with
any means of creating suction or pressure ; and the tubes
themselves, though highly elastic, are non-contractile, and
must be distended or emptied \>y some external force. Many
Insects, especially such as fly rapidly, exhibit rhythmical move-
ments of the abdomen. There is an alternate contraction and
dilatation, which may be supposed to be as capable of setting
up expirations and inspirations as the rise and fall of the
diaphragm of a Mammal. In many Insects, two sets of
muscles serve to contract the abdomen — viz., muscles which
compress or flatten, and muscles which approximate or tele-
scope the segments.* In the Cockroach the second set is feebly
developed, but the first is more powerful, and causes the terga
and sterna alternately to approach and separate with a slow,
rhythmical movement ; in a Dragon-fly or Humble-bee the
action is much more conspicuous, and it is easy to see that the
abdomen is bent as well as depressed at each contraction. No
special muscles exist for dilating the abdomen, and this seems
to depend entirely upon the elasticity of the parts. It was

* This subject is treated at greater length in Prof. Plateau's contribution on
Respiratory Movements of Insects. (Infra, p. 159.)

THE ORGANS OF CIRCULATION AND RESPIRATION. 157

long supposed that, when the abdomen contracted, air was
expelled from the body, and the air passages emptied ; that
when the abdomen expanded again by its own elasticity, the
air passages were refilled, and that no other mechanism was
needed. Landois pointed oat, however, that this was not
enough. Air must be forced into the furthest recesses of the

tracheal system, where the exchange of oxygen and carbonic
acid is effected more readily than in tubes lined by a dense

•J t/

intima. But in these fine and intricate passages the resistance
to the passage of air is considerable, and the renewal of the air
could, to all appearance, hardly be effected at all if the inlets
remained open. Landois accordingly searched for some means
of closing the outlets, and found an elastic ring or spiral, which
surrounds the tracheal tube within the spiracle. By means of
a special muscle, this can be made to compress the tube, like
a spring clip upon a flexible gas pipe. When the muscle
contracts, the passage is closed, and the abdominal muscles can
then, it is supposed, bring any needful pressure to bear upon
the tracheal tubes, much in the same way as with ourselves,
when we close the mouth and nostrils, and then, by forcible
contraction of the diaphragm and abdominal walls, distend the
cheeks or pharynx. Landois describes the occluding apparatus
of the Cockroach as completely united with the spiracle. It
consists, according to him, of two curved rods, the " bow " and
the " band/' one of which forms each lip of the orifice. From
the middle of the band projects a blunt process for the attach-
ment of the occlusor muscle, which passes thence to the
extremity of the bow. The concave side of each rod is fringed
with setoo, and turned towards the opening, which lies between
the two. Upon this description of the spiracles of the Cock-
roach we have to remark that there is no occluding apparatus
at all in the thoracic spiracles, which are provided with
external valves. In the abdominal spiracles the bow is per-
fectly distinct, but the " band ' of Landois has no separate
existence. Though the actual mechanism in this Insect does
not altogether agree with Landois' description, it is capable
of performing the physiological office upon which he justly
lays so much stress — viz., the closing of the outlets of the
tracheal system, in order that pressure may be brought upon
the contained air.

158 THE COCKROACH :

The injection of air by muscular pressure into a system of
very fine tubes may, however, appear to the reader, as it
formerly did to ourselves, extremely difficult or even impossible.
Can any pressure be applied to tubes within the body of an
Insect which will force air along the passages of (say) '0001 in.
diameter ? It may well seem that no pressure would suffice to
distend these minute tubules, in which the actual replacement
of carbonic acid by oxygen takes place, but that the air would
either contract to a smaller volume or burst the tissues.

If we question the physical possibility of Landois' explana-
tion, an alternative is still open to us. The late Prof. Graham
has applied the principle of Diffusion to the respiration of
animals, and has shown how by a diffusion-process the carbonic
acid produced in the remote cavities would be moved along the
smaller tubes, and emptied into wider tubes, from which it
could be expelled by muscular action. The carbonic acid is
not merely exchanged for oxygen, but for a larger volume of
oxygen (0 95 : C 02 81) ; and there is consequently a tendency
to accumulation within the tubes, which is counteracted by the
elasticity of the air vessels, as well as by special muscular
contractions.*

Whether diffusion or injection by muscular pressure is
the chief means of effecting the interchange of gases between
the outer air and the inner tissues of the Insect, is a question
to be dealt with by physical enquiry.

If we suppose two reservoirs of different gases at slightly
different pressures to be connected by a capillary tube of
moderate dimensions, such as one of the larger tracheae of the
Cockroach, transference by the molecular movements of diffu-
sion would be small compared with that effected bv the flow

* *j

of the gas in mass. But if the single tube were replaced
by a number of others, of the same total area, but of the
fineness (say) of the pores in graphite, the flow of the gas
would be stopped, and the transference would be effected by
diffusion only. We may next consider tubes of intermediate
fineness, say a tracheal tubule of the Cockroach at the point

* Phil. Mag., 1833. Reprinted in "Researches," p. 44. Graham expressly applies
the law of diffusion of gases to explain the respiration of Insects. Sir John Lubbock
quotes and comments upon the passage in his paper on the Distribution of the
Tracheae in Insects. (Linn. Trans. Vol. XXIII.)

THE ORGANS OF CIRCULATION AND RESPIRATION. 159

where the spiral thread ceases, and where the exchange of
gases through the wall of the tubule becomes comparatively
unobstructed. Such a tubule is about '0001 in. diameter. If
we may extend to such tubules the laws which hold good for
the flow of gases in capillary tubes of much greater diameter,
the quantity of air which might be transmitted in a given time
by muscular pressure of known amount can be determined.
Suppose the difference of pressure at the two ends of the tubule
to be one-hundredth of an atmosphere, and further, that the
tubule is a quarter of an inch long and "0001 in. diameter.
The tubule would then be cleared out every four seconds. Such
a flow of air alon^ innumerable tubules might well suffice for

o <->

the respiratory needs of the Cockroach. Without laying too
much stress upon this calculation, for which exact data are
wanting, we may be satisfied that an appreciable quantity of
air may be made by muscular pressure to flow along even the
finer air passages of an Insect.*

Respiratory Movements of Insects.

BY FELIX PLATEAU, PROFESSOR IN THE UNIVERSITY OF GHENT.

The respiratory movements of large Insects are in general
very apparent, and many observers have said something about
what they have seen in various species. It is only since the
publication of Rathke's memoir, however, that precise views
have been gained as to the mechanism of these movements.
This remarkable work, treating of the respiratory movements
in Insects, the movable skeletal plates, and the respiratory
muscles characteristic of all the principal groups, filled an
important blank in our knowledge. But, notwithstanding the
skill displayed in this research, many questions still remained
unanswered, which required more exact methods than mere
observation with the naked eye or the simple lens.

The writer, who was followed a year later by Langendorff,
conceived the idea of studying, by such graphic methods as are
now familiar, the respiratory movements of perfect Insects. He

* For an explanation of the physical principles involved in this discussion, and
for the calculation (based upon our own assumptions), we are indebted to Mr. A. "W.
Ptiicker, F.R.S

160 THE COCKROACH :

has made use of two modes of investigation. The first, or graphic
method, in the strict sense of the term, consisted in recording
upon a revolving cylinder of smoked paper the respiratory
movements, transmitted by means of very light levers of Bristol
board, attached to any selected part of the Insect's exoskeleton.
Unfortunately, this plan is only applicable to insects of more
than average size. A second method, that of projection, con-
sisted in introducing the Insect, carried upon a small support,
into a large magic lantern fitted with a good petroleum lamp.
When the amplification does not exceed 12 diameters, a sharp
profile may be obtained, upon which the actual displacements
may be measured, true to the fraction of a millimetre. Placing
a sheet of white paper upon the lantern screen, the outlines of
the profile are carefully traced in pencil so as to give two
superposed figures, representing the phases of inspiration and
expiration respectively. By altering the position of the Insect,
so as to obtain profiles of transverse section, or of the different
parts of the body, and, further, by gluing very small paper slips
to parts whose movements are hard to observe, the successive
positions of the slips being then drawn, complete information
is at last obtained of every detail of the respiratory movements :
nothing is lost.

This method, similar to that employed by the English phy-
siologist, Hutchinson,* is valuable, because it enables us, with a
little practice, to investigate readily the respiratory movements
of very small Arthropods, such as Flies or Lady-birds. It has
this advantage over all others, that it leaves no room for errors
of interpretation.

Not satisfied with mere observation by such means as these,
of the respiratory movements of Insects, the writer has also
studied the muscles concerned, and, in common with other
physiologists (Faivre, Barlow, Luchsinger, Donhoff, and Langen-
dorff), has examined the action of the various nervous centres
upon the respiratory organs. The results at which he has
arrived may be summarised as follows : —

1. There is no close relation between the character of the
respiratory movements of an Insect and its position in the
zoological system. Respiratory movements are similar only

* J. Hutchiuson, Art. Thorax, Todd's Cycl. of Anat. and Phys.

THE ORGANS OF CIRCULATION AND RESPIRATION. 161

when the arrangement of the abdominal segments, and
especially when the disposition of the attached muscles are
almost identical. Thus, for example, the respiratory movements
of a Cockroach are different from those of other Orthoptera, but
resemble those of Hemiptera Heteroptera.

2. The respiratory activity of resting Insects is localised in
the abdomen. Y. Gfraber has expressed this fact in a picturesque
form, by saying that in Insects the chest is placed at the hinder
end of the body.

3. In most cases the thoracic segments do not share in the
respiratory movements of an Insect at rest. Among the singular
exceptions to this rule is the Cockroach (P. orientalis), in which
the terga of the meso- and meta- thoracic segments perform
movements exactly opposite in direction to those of the
abdomen. (See fig. 89, Ms. th, Mt. th.)

Fig. 89. — Profile of Cockroach (P. orientalis}. The black surface represents the
expiratory contour, while the inspiratory is indicated by a thin line. The
arrows show the direction of the expiratory movement. Ms. th., mesothorax ;
Mt. th., metathorax. Reduced from a magic-lantern projection.

4. Leaving out of account all details and all exceptions, the
respiratory movements of Insects may be said to consist of
alternate contraction and recovery of the figure of the abdomen
in two dimensions — viz., vertical and transverse. During ex-
piration the diameters in question are reduced, while during
respiration they revert to their previous amounts. The trans-
verse expiratory contraction is often slight, and may be imper-
ceptible. On the other hand, the vertical expiratory contraction
is never absent, and usually marked. In the Cockroach (P.

«/

orientalis) it amounts to one-eighth of the depth of the abdomen
(between segments 2 and 3).

162 THE COCKROACH:

5. Three principal types of respiratory mechanism occur in
Insects, and these admit of further subdivision : —
(a) Sterna usually stout and very convex, yielding but little.
Terga mobile, rising and sinking appreciably. To this
class belong all Coleoptera, Hemiptera Heteroptera, and
Blattina (Orthoptera).

Fig. 90. — Transverse section of Abdomen, Lamellicorn Beetle. The position
of the terga and sterna after an inspiration, is indicated by the thick line ; the
dotted line shows their position after an expiration, and the arrow marks the
direction of the expiratory movement.

In the Cockroach (Penplaneta) the sterna are slightly
raised during expiration. (See figs. 89 and 91.)

Fig. 91. — Transverse section of Abdomen, Cockroach (P. orientalis)-

(b) Terga well developed, overlapping the sterna on the sides

of the body, and usually concealing the pleural membrane,
which forms a sunk fold. The terga and sterna approach
and recede alternately, the sterna being almost always the
more mobile. To this type belong Odonata, Diptera,
aculeate Hymenoptera, and Acridiaii Orthoptera. (Fig. 92.)

sterna, is well developed and exposed on the sides of the
body. The terga and sterna approach and recede alter-
nately, while the pleural zone simultaneously becomes
depressed or returns to its original figure. To this type
the writer assigns the Locustidce, the Lepidoptera and the
true Neuroptera (excluding Phryganidac). (Fig. 93.)

THE ORGANS OF CIRCULATION AND RESPIRATION. 163

Fig. 92. — Transverse section of Abdomen, Bee (Bornbus}.

6. Contrary to the opinion once general, changes in length
of the abdomen, involving protrusion of the segments and sub-
sequent retraction, are rare in the normal respiration of Insects.
Such longitudinal movements extend throughout one entire
group only — viz., the aculeate Hymenoptera. Isolated examples
occur, however, in other zoological divisions.

Fig. 93. — Transverse section of Abdomen, Hawk Moth (Sphingina).

7. Among Insects sufficiently powerful to give good graphic
tracings, it can be shown that the inspiratory movement is
slower than the expiratory, and that the latter is often
sudden.

8. In most Insects, contrarv to what obtains in Mammals,

onty the expiratory movement is active ; inspiration is passive,
and effected by the elasticity of the body- wall.

9. Most Insects possess expiratory muscles only. Certain
Diptera (Calliphora vomitoria and Eristalis tcnax) afford the
simplest arrangement of the expiratory muscles. In these
types they form a muscular sheet of vertical fibres, connecting
the terga with the sterna, and underlying the soft elastic mem-
brane which unites the hard parts of the somites. One of the

164 THE COCKROACH:

most frequent complications arises by the differentiation of this
sheet of vertical fibres into distinct muscles, repeated in every
segment, and becoming more and more separated as the sterna
increase in length. (See the tergo-sternal muscles of the
Cockroach, fig. 36, p. 76.) Special inspiratory muscles occur in
Hymenoptera, Acridiidoo, and Phryganidoc.

10. The abdominal respiratory movements of Insects are
wholly reflex. Like other physiologists who have examined
this side of the question, the writer finds that the respiratory
movements persist in a decapitated Insect, as also after destruc-
tion of the cerebral ganglia or oesophageal connectives ; further,
that in Insects whose nervous system is not highly concentrated
(e.g., Acridiidic and Dragon-flies), the respiratory movements
persist in the completely-detached abdomen ; while all external
influences which promote an increased respiratory activity in
the uninjured animal, have precisely the same action upon
Insects in which the anterior nervous centres have been
removed, upon the detached abdomen, and even upon isolated
sections of the abdomen.

The view formerly advocated by Faivre, that the metathoracic
ganglia play the part of special respiratory centres, must be
entirely abandoned. All carefully performed experiments on
the nervous system of Arthropoda have shown that each
ganglion of the ventral chain is a motor centre, and in Insects
a respiratory centre, for the somite to which it belongs. This
is what Barlow calls the "self-sufficiency " of the ganglia.

The writer has made similar observations upon the respiration
of Spiders and Scorpions ; * but to his great surprise he has been
unable either by direct observation, or by the graphic method,
or by projection, to discover the slightest respiratory movement
of the exterior of the body. This can only be explained by
supposing that inspiration and expiration in Pulmonate
Arachnida are intra-pulmonary, and affect only the proper
respiratory organs. The fact is less surprising because of
the wide zoological separation between Arachnida and
Insects.

* De 1'absence de mouvements respiratoires perceptibles chez les Arachnides
(Archives de Biologie de Yan Beneden et Van Bambeke, 1885.)

THE ORGANS OF CIRCULATION AND RESPIRATION. 165

Respiratory Activity of Insects.

The respiratory activity of Insects varies greatly. Warmth,
feeding, and movement are found to increase the frequency
of their respirations, and also the quantity of carbonic acid
exhaled. In Liebe's* experiments a Carabus produced "24 mgr.
of carbonic acid per hour in September, but only '09 mgr. per
hour in December. A rise of temperature raised the product
temporarily to twice its previous amount ; but when the same
insect was kept under experiment for several days without food,
the amount fell in spite of its increased warmth. Treviranusf
gives the carbonic acid exhaled by a Humble-bee as varying
from 22 to 174, according as the temperature varied from
56° to 74° F.

Larvae often breathe little, especially such as lie buried in
wood, earth, or the bodies of other animals. The respiration of
pupae is also sluggish, and not a few are buried beneath the
ground or shrouded in a dense cocoon or pupa-case. Muscular
activity originates the chief demand for oxygen, and accordingly
Insects of powerful flight are most energetic in respiration.

A rise of temperature proportionate to respiratory activity
has been observed in many insects. Newport .J tells us how the
female Humble-bee places herself on the cells of pupae ready
to emerge, and accelerates her inspirations to 120 or 130 per
minute. During these observations he found in some instances
that the temperature of a single Bee was more than 20° above
that of the outer air.

Some Insects can remain long without breathing. They
survive for many hours when placed in an exhausted receiver,
or in certain irrespirable gases. Cockroaches in carbonic acid
speedily become insensible, but after twelve hours' exposure to
the pure gas they revive, and appear none the worse.
H. Muller§ says that an Insect, placed in a small, confined
space, absorbs all the oxygen. In Sir Humphry Davy's
"Consolations in Travel "|| is a description of the Lago dei

* Ueb. d. Respiration der Tracheaten. Chemnitz (1872).

t See table in Burmeister's " Manual," Eng. trans, p. 398.

J Art. " Insecta," Cyc. Anat. and Phys., p. 989.

§ Pogg. Ann, 1872, Hft. 3.

|| "Works, Vol. IX., p. 287. This passage has been cited by Rathke.

166 THE COCKROACH.

Tartari, near Tivoli, a small lake whose waters are warm and
saturated with carbonic acid. Insects abound on its floating
islands ; though water birds, attracted by the abundance of
food, are obliged to confine themselves to the banks, as the
carbonic acid disengaged from the surface would be fatal to
them, if they ventured to swim upon it when tranquil.

Or lorn of Tracheal Respiration.

Kowalewsky, Butschli, and Hatschek have described the
first stages of development of the tracheal system. Lateral
pouches form in the integument ; these send out anterior and
posterior extensions, which anastomose and form the longi-
tudinal trunks. The tracheal ramifications are not formed
by a process of direct invagination, but by the separation of
chitinogenous cells, which cohere into strings, and then form
irregular tubules. The cells secrete a chitinous lining, and

o O'

afterwards lose their distinct contours, fusing to a continuous
tissue, in which the individual cells are indicated only by their
nuclei, though by appropriate re-agents the cell boundaries can
be defined.

The ingenious hypothesis propounded by Gegenbaur, that
the tracheal tubes of Insects were originally adapted to aquatic
respiration, and that the stigmata arose as the scars of disused
tracheal gills, has been discussed in chap. iv. Semper has
suggested* that tracheoe may be modified segmental organs, but
the most probable view of their origin is that put forth by
Moseley,f that they arose as ramified cutaneous glands. In
Peripatus the openings are distributed irregularly over the
body ; the external orifices lead to pits, from which simple
tubes, with but slight spiral markings, extend into the deeper
tissues.

* Arbeiten a. d. Zool. Zoot. lust. Wurzburg. Bd. ]!., 1874.
t Phil. Trans., 1874, p. 757.

CHAPTER IX

REPRODUCTION.

SPECIAL REFERENCES.

BRANDT, A. Ueber die Eirohren der Blatta (Periplaneta) orientalis. Mem. Acad.
St. Petersb. Ser. 7, Vol. XXI. (1874). [Ovarian Tubes of Cockroach.]

LACAZE-DUTHIERS. Rech. sur 1'armure genitale femelle des Insectes Orthopteres.
Ana. Sci. Xat., Zool., 3e Ser., Tom. XVII. (1852). [External reproductive organs
of female Orthoptera.]

BERLESE. Ricerde sugli organi genitali degli Ortotteri. Atti della R. Acad. dei
Lincei. Ser. 3, Vol. XL (1882). [Genital Organs of European Orthoptera.]

KADTI. Beitr. zur Vorgiinge beim. Eierlegen der Blatta Orientalis. Vorlaufige
Mittheilung. Zool. Anz., 1879, p. 632. [Formation of egg-capsules of Cockroach.]

BREHM. Comparative structure of the reproductive organs in Blatta germanica
and Periplaneta orientalis. Mem. Soc. Ent. St. Petersb., Tom. VIII. (1880). In
Russian. [Male organs only.]

RAJEWSKY. TJeber die Geschlechtsorgane von Blatta orientalis, &c. Nachr. d.
kais. Gesellsch. d. Moskauer Universitiit. , Bd. XVI. (1875). [Testes of Cockroach.
The original paper is in Russian ; an abstract is given in Hofmann and Schwalbe's
Jahresbericht, 1875, p. 425.]

BUTSCHLI. Ban u. Entwickelung d. Satnenfaden bei Insekten u. Crustaceen.
Zeits. f. wiss. Zool., Bd. XXL, pp. 402-114; 520-534. PI. xl. xli. (1871).
[Spermatozoa and spermatogenesis in the Cockroach.]

LA VALETTE ST. GEORGE. Spermatologische Bedtriige, II. Blatta germanica.
Arch. f. mikr. Anat., Brl. XXVII. (1886). [Spermatogenesis in B. germanica.]

MORAVITZ. Quaedam ad anat. Blattre germanicpe pertinentia. Dissertatio inaugu-
ralis. Dorpat. (1853). [An excellent early account of the anatomy of B. r/ermanica,
including a description of the male and female organs. The figures are not
trustworthy.]

Female Reproductive Organs.

The ovaries of the two sides of the body are .separated, as in
most Insects, and consist on each side of eight tubes, four
dorsal and four ventral, which open into the inner side of a
common oviduct. The two oviducts unite behind, and form a
very short uterus. Tracheae and fat-cells tie the ovarian tubes

168

THE COCKROACH :

of each side together into a spindle-shaped bundle. Each tube
is about '4 in. long, and has a beaded appearance, owing to the
eggs which distend its elastic wall. It gradually tapers in
front ; then suddenly narrows to a very small diameter ; and
lastly, joins with the extremities of the other tubes to form a
slender solid filament, which passes towards the heart, and
becomes lost in the fat-body. The wall of an ovarian tube
consists of a transparent elastic membrane, lined by epithelium,
and invested externally by a peritoneal layer of connective
tissue.

Fig. 94. — Female Reproductive Organs. Od, oviduct ; CG, colleterial gland. X 14.

The epithelium of an ovarian tube presents some remarkable
peculiarities which disguise its true character. High up in the
tube, the narrow lumen is occupied by a clear protoplasm, in
which nuclei, but no cell walls, can be discerned. Where the
tube suddenly widens, large rounded and nucleated masses of

* •

protoplasm appear, interspersed with nuclei entangled in a

REPRODUCTION.

169

network of protoplasm. Passing down the tube, the large
cells, which can now be recognised as eggs, arrange themselves
in a single row, to the number of about twenty. They are at
first polygonal or squarish, but gradually become cylindrical,
and finally oval. Between and around the eggs the nuclei
gradually arrange themselves into one-layered follicles, which
are attached, not to the wall of the tube, but to the eggs, and
travel downwards with them. As the eggs descend, the yolk
which they contain increases rapidly, and the germinal vesicle

Fig. 95. — Ovarian Tube (acetic acid preparation), showing scattered nuclei (upper
figure), which ultimatelj* form follicles around the ova (lower figure). Copied
from Brandt, loc. cit.

170 THE COCKROACH :

and spot (nucleus and nucleolus), which were at first very
plain, disappear. A vitelline membrane is secreted by the
inner surface, and a chitinous chorion by the outer surface of

the egg-follicle.

The lowest egg in an ovarian tube is nearly or altogether of
the full size ; it is of elongate-oval figure, and slightly curved,
the convexity being turned towards the uterus. It is filled
with a clear albuminous fluid, which mainly consists of yolk.
The chorion now forms a transparent yellowish capsule, which
under the microscope appears to be divided up into very many
polygonal areas, defined by rows of fine dots. These areas
probably correspond to as many follicular cells. The convex
surface of the chorion is perforated by numerous micropyles,
fine pores through which it is probable the spermatozoa gain
access to the interior of the egg.

The uterus has a muscular wall and a chitinous lining. Two
repeatedly branched colleterial glands open into its under side.
Of these the left is much the larger, and overlies the other.
It consists of many clichotomous tubes, some of which are a

little dilated at their blind ends. The gland is much entangled
with fat-cells, which make it difficult to unravel. The right
gland is probably of no functional importance ; the left gland
is filled with a milky substance, containing many crystals and
a coagulable fluid, out of both of which the egg-capsule is
formed.*

At its hinder end the uterus opens by a median vertical slit,
which lies in the 8th sternum, into a genital pouch which
represents part of the external integument, folded back far into
the interior of the abdomen. (See fig. 96.) Upon the dorsal
wall of the genital pouch the orifice of the sperniatheca is
situated.-)* This is a short tube dilated at the end, and wound

* The crystals have been supposed to consist of oxalate of lime (Duchamp, Rev.
des sci. nat. Montpellier, Tom. VIII.). Hallez observes that they are prismatic, with
rhombic base, the angles truncated. They are insoluble in water and weak nitric
acid, but dissolve rapidly in strong sulphuric acid without liberation of gas, and still
more rapidly in caustic potash. (Compt. Rend., Aug., 1S85.)

f It is usually stated that the spermatheca of the Cockroach opens into the
uterus, as it does in most other Insects, but this is not true. Locusts and Grass-
hoppers have the outlet of the spermatheca placed as in the Cockroach ; in other
European Orthoptera, it lies upon the dorsal wall of the uterus. (Berlese, loc. cit.,
p. 273.)

REPRODUCTION". 171

into a spiral of about one turn. From the tube a csecal process
is given off, which may correspond with the accessory gland
attached to the duct of the spermatheca in many Insects (e.g.,
Coleoptera, Hymenoptera, and some Lepidoptera). The sperma-
theca is filled during copulation, and is always found to contain

Fig. 96. — Diagram to show the theoretical (upper figure) arid actual position of the
hinder abdominal sterna in the female Cockroach. V, uterus ; s, spermatheca.
The nerve-cord is introduced into both figures.

spermatozoa in the fertile female.* The spermatozoa are no
doubt passed into the genital pouch from time to time, and
there fertilise the eggs descending from the ovarian tubes.

•T1 <^ O

The external reproductive organs of the female Cockroach
belong to the 7th, 8th, and 9th somites. The 7th sternum is
incompletely divided into anterior and posterior sections, and
the posterior section is split into lateral halves. These are
joined by a flexible membrane, which admits of the wide
separation of the halves, when copulation or the passage of the
large egg-capsule renders it necessary. The vertical faces of
the membrane, which are pressed together when the parts are
at rest, are stiffened by chitinous thickenings.

If the succeeding sterna retained their proper place, as they
do in some Orthoptera (e.g., the Mole Cricket), the 8th and 9th
sterna would project beyond the 7th, while the rectum would

It is a striking proof of the sagacity of Malpighi, that he should have observed
in the Silkworm the spermatophore of the male ( " in spiram circurnvolutum per-
siruile semen") and the spermatheca of the female. His reasoning as to the
function of the spermatheca wanted nothing but microscopic evidence of the actual
transference of spermatozoa to establish it in all points. Audouin and Siebold
supplied what was wanting nearly two centuries later, but they mistook the spirally
wound spermatophore for a broken-off penis, and Stein ("NVeibl. Geschlechtsorgane
der Kilfer, p. 85) first arrived at the complete proof of Malpighi's explanation.

172

THE COCKROACH

open beneath the last tergum, and the uterus between the 8th
and 9th sterna. In the adult female Cockroach, however, the
8th and 9th somites are telescoped into the 7th, and completely
hidden by it. Their terga are reduced to narrow bands. The
8th sternum forms a semi-transparent plate which slopes down-
wards and backwards, and is pierced by a vertical slit, the
outlet of the uterus. The upper edge of this sternum is hinged

Fig. 97. — Hinder end of abdomen of female Cockroach. In the upper figure the
halves of the 7th sternum are closed ; in the lower figure they are open.

upon the projecting basis of the anterior gonapophyses (to be
described immediately), and the parts form a kind of spring
joint, ordinarily closed, but capable of being opened wide upon
occasion. The 9th sternum is a small median crescentic plate,
distinct from the 8th ; it supports the spermatheca, whose duct
traverses an oval plate which projects from the fore-edge of
the sternum.

By the telescoping of the 8th and 9th somites the sterna
take the position shown in fig. 96J?, and a new cavity, the
genital pouch, is formed by iiivagination. This receives the
extremity of the body of the male during copulation, while it
serves as a mould in which the egg-capsule is cast during
oviposition. Its chitinous lining resembles that of the outer

REPRODUCTION".

173

integument. The uterus opens into its anterior end, which is
bounded by the 8th sternum ; the spertnatheca opens into its
roof, which is supported by the 9th sternum and the gonapop-
hyses ; while its floor is completed by the 7th sternum and
the infolded chitinous membrane.

Fig. 98. — External Reproductive Organs of Female. Ts, &c., terga ; S~ , &c.,
sterna; G, anterior gonapophysis ; Gl, its base; (/, posterior gonapophyses ;
Od, oviduct ; sp, spermatheca ; R, rectum. The upper figure shows the parts
in oblique profile ; the left lower figure is an oblique view from before of the
outlet of the uterus, the anterior gonapophyses being cut short ; the right lower
figure shows the gonapophyses. Arrows indicate the outlet of the oviduct and
uterus.

A pair of appendages (anterior gonapophyses) are shown by
the development of the parts to belong to the 8th somite.

174 THE COCKROACH:

They are slender, irregularly bent, and curved inwards at the
tips. A small, forked, chitinous slip connects them with both
the 8th and 9th terga, but their principal attachment is to the
upper (properly, posterior) edge of the 8th sternum. The
anterior gonapophyses expand at their bases into broad hori-
zontal plates, which form part of the roof of the genital pouch.

Two pairs of appendages, belonging to the 9th somite, form
the posterior gonapophyses. The outer pair are relatively
large, soft, and curved : the inner narrow, hard, and straight.*

The anterior gonapophyses form the lower, and the posterior
the upper jaw of a forceps, which in many Insects can be
protruded beyond the body. Some of the parts are often armed
with teeth, and the primary use of the apparatus is to bore
holes in earth or wood for the reception of the eggs. Hence
the apparatus is often called the ovipositor. It forms a promi-
nent appendage of the abdomen in such Insects as Crickets,
Saw-flies, Sirex, and Ichneumons. The sting of the Bee is a
peculiar adaptation of the same organ to a very different
purpose. In the Cockroach the ovipositor is used to grasp the
egg-capsule, while it is being formed, filled with eggs, and
hardened ; and the notched edge (fig. 5, p. 23) is the imprint
of the inner posterior gonapophyses, made while the capsule is
still soft. The shape of the parts in the male and female
indicates that the ovipositor is passive in copulation, and is
then raised to allow access to the spermatheca.

Male Reproductive Organs.

The male reproductive organs of Insects, in spite of very
great superficial diversity, are reducible to a common type,
which is exemplified by certain Coleoptera. The essential parts
are (1) the festes, which in their simplest form are paired,
convoluted tubes ; more commonly they branch into many
tubules or vesiculce, while thev may become consolidated into a

V • >

* The descriptions and figures of the reproductive appendages of female Orthop-
tera by Lacaze-Duthiers (Ann. Sci. Nat., 1852) are so often consulted, that it may
be useful to explain how we understand and name the same parts. In pi. xi., fig. 2,
8' and 0' are the 8th and 9th terga ; the anterior gonapophyses are seen to be
attached to them below ; a (figs. 2 and 4) is the base of the same appendage, but the
twisted ends are incorrect ; the 8th sternum is seen at the back (figs. 2 and 4) ;
a' represents the outer, / the inner pair of posterior gonapophyses.

REPRODUCTION. 175

single organ ; (2) long coiled vasa deferentia, opening into or
close to (3) paired vesiculce seminales, which discharge into
(4) the ejaculatory duct, a muscular tube, with chitinous lining,
by which the spermatozoa are forcibly expelled. Opening into
the vesiculce seminales, the ejaculatory duct, or by a distinct
external orifice, may be found (5) accessory glands, very
variable in form, size, and number. More than one set may
occur in the same Insect. To these parts, which are rarely
deficient, are very often appended an external armature of
hooks or claspers.

The male Cockroach will be found to agree with this
description. It presents, however, two peculiarities which are
uncommon, though not unparalleled. In the first place the
testes are functional only in the young male. They subsequently
shrivel, and are functionally replaced by the vesiculse seminales
and their appendages, where the later transformations of the
sperm-cells are effected. The atrophied testes are nevertheless
sufficiently large in the adult to be easily made out. Secondly,
the accessory glands are numerous, and differ both in function
and insertion. Two sets are attached to the vesiculae seminales,
and the fore end of the ejaculatory duct (ntriculi majores and
breviores) ; another large conglobate gland opens separately to
the exterior. We shall now describe the structure of these parts
in more detail.*

The testes may be found in older larvae or adults beneath
the fifth and sixth terga of the abdomen. They lie in the
fat-body, from which they are not very readily distinguished.
Each testis consists of 30-40 rounded vesicles attached by
short tubes to the vas deferens.f The wall of the testis

We propose to notice here the chief differences which we have found between
the figures of Brehm (loc. cit.), which are the fullest and best we have seen, and our
own dissections.

Figs. 10, 11 (pp. 169-70). The ejaculatory duct and duct of the conglobate gland
are made to end in the penis (infra, p. 178).

Figs. 14, 15 (p. 173). These figures seem to us erroneous in many respects, such
as the median position of the penis and titillator.

Fig. 16 (p. 174). The pair of hooks marked E are too small, and there are additional
plates at the base, which are not figured (see our fig. 102). F (of our fig.) is
omitted.

f In Blatta yermanica the testes are functional throughout life. They consist of
four lobes each. The vasa deferentia are much shorter than in P. orientalis.

17G

THE COCKROACH

consists of a peritoneal layer and an epithelium, which is folded
inwards along transverse lines. The cells of the epithelium
give rise to spermatocysts,* which enclose sperm cells. By

Fig. 99.— 1. Male Organs, ventral view. Ts, testis ; VD, vas deferens ; DE,
cluctus ejaculatorius ; U, utriculi majores ; u, utriculi breviores. 2. Do.,
dorsal view, showing termination of vasa deferentia. 3. Conglobate gland, and
its duct. X 8.

division of the nuclei of the sperm cells spermatozoa are
formed, which have at first nucleated heads and long tails.

* The spermatocysts are peculiar to Insects and Amphibia. They arise by
division of the spermatospores, or modified epithelial cells, and form hollow cysts,
within which sperm cells (or spermatoblasts) are developed by further division.
The sperm cells are usually placed radiately around the wall of the spermatocyst.
They escape by dehiscence, and are transformed into spermatozoa.

REPRODUCTION.

177

Subsequently the enlarged heads disappear. The spermatozoa
move actively. In adult males the testes undergo atrophy,
but can with care be discovered in the enveloping fat-body.

The vasa deferentia are about "25 inch in length. They pass
backwards from the testes, then turn downwards on each side
of the large intestine, and finally curve upwards and forwards,
entering the vesiculae seminales on their dorsal side. Each vas
deferens divides once or twice into branches, which immediately
reunite ; in the last larval stage the termination of the passage
dilates into a rounded, transparent vesicle.

Fig. 100. — Male Organs, side view. T~ , seventh tergum ; S~ , seventh sternum;
Ts, DE, as before. A, E, see fig. 102. X 8.

The vesiculse seminales are simple, rounded lobes in the
pupa (fig. 101), but their appearance is greatly altered in the
adult by the development of two sets of utricles (modified
accessory glands). The longer utricles (utricnli majores) open
separately into the sides of the vesiculee ; nearer to the middle
line are the shorter and more numerous utriculi breviores, which
open into the fore part of the vesiculse.

The utricles form the " mushroom-shaped gland" of Huxley,
which was long described as the test-is. In the adult male the
utricles are usually distended with spermatozoa, and of a
brilliant opaque white.

178 THE COCKROACH :

The ejaculatory duct is about '15 inch long, and overlies
the 6th-9th sterna. It is wide in front, where it receives the
paired outlets of the vesiculce seminales. Further back it
narrows, and widens again near to its outlet, which we find to
be between the external chitinous parts, and not into the penis,
as described by Brehm. The duct possesses a muscular wall
for the forcible ejection of its contents, and in accordance with
its origin as a folding-in of the outer surface, it is provided
with a chitinous lining. In the adult the fore part of the duct
may be distended with spermatozoa.

Fig. 101. — Vesiculse Seminales and Ductus Ejaculatorius of Pupa. FZ>, vas
cleferens. X 28.

The ejaculatory duct is originally double (p. 194), and its
internal cavity is still subdivided in the last larval stage or
so-called " pupa."

Upon the ventral surface of the ejaculatory duct lies an
accessory gland of unknown function ; it is " composed of
dichotomous, monilated tubes, lined by a columnar epithelium,
all bound together by a common investment into a flattened,
elongated mass." * The duct of this gland does not enter the
penis, as described by Brehm, but opens upon a double hook,
which forms part of the external genital armature (fig. 99, 3).
It may be convenient to distinguish this as the " conglobate
gland."f

* Huxley, Anat. Invert. Animals, p. 416.

f The term "accessory gland," used by Huxley and others, is already appropriated
to glands which we believe to be represented by the utricles of the Cockroach, and
which have only a general correspondence with the gland in question.

REPRODUCTION.

179

The external reproductive organs of the male Cockroach are
concealed within the 9th sternum. The so-called penis (fig. 102)
is long, slender, and dilated at the end. It is not perforated,
and we do not understand its use, though it probably conveys
the semen.

Fig. 102. — External Male Organs, separated. The lettering agrees with Brehm's
figures. A, titillator; B, penis; C — F, hooks and plates. X 8.

The " titillator ' (B runner von Wattenwyl) is a solid curved
hook with a hollow base. Besides these, are several odd-shaped,
unsymmetrical pieces (fig. 102, C, Dy E, F\ moved b}^ special
muscles. A pair of styles (see figs. 32-3 and 103) project from
the hinder edge of the 9th sternum. These paired and unpaired
appendages are believed to open the genital pouch of the female,
but we do not understand their action in detail.*

Brehm observes that the male reproductive organs of the
Cockroach are most nearly paralleled by those of the Mantidao.
A free penis occurs in all Orthoptera, except Acridiidae and
Phasmidse.

The male organs of the House Cricket will be found much
easier to understand than those of the Cockroach. The testes
are of irregular, oval figure, the vasa deferentia very long,

e Similar organs, forming a male genital armature, have been described in various
Insects. See Burmeister, Man. of Entomology, p. 328 (Eng. Transl.); Siebold, Anat.
of Invertebrates; Gosse in Linn. Trans., Ser. 2, Yol. II. (1883); Burgess on Milk-weed
Butterfly, Ann. Mem. Bost. Soc. Nat. Hist.; &c.

180 THE COCKROACH.

tortuous, and enlarged towards the middle of their length.
The vesiculrc seminales bear many utriculi majores et breviores.
The penis is of simple form, and dilated at the end. The
titillator is broad, but produced into a slender prong, which
projects beyond the penis. A pair of subanal styles is found,
but the unpaired booklets are wanting or very inconspicuous.

Fig. 103. — The Tenth Tergiim reflected to show the external male organs in situ.
T10, tenth tergum ; p, podical plates ; A — F, as in fig. 102 ; 8, sub-anal styles.
X 8.

Yery little is known about the act of copulation among Cock-
roaches, and the opportunities of observation are few. The
following account is given by Cornelius (loc. cit., p. 22) : —

" The male and female Cockroaches associate in pairs, the females being
generally quiet. The male, on the contrary, bustles about the female,
runs round her, trailing his extended abdomen on the ground, and now
and then raises his wings. If the female moves away, the male stops the
road. At last, when the female has become perfectly still, the male goes
in front of her, brings the end of bis abdomen towards her, then moves
backwards, and pushes his whole length under the female. The operation
is so rapid that it is impossible to give an exact account of the circum-
stances. Then the male creeps out from beneath the female, raises high
both pairs of wings, depresses them again, and goes off, while the female
usually remains quiet for some time."

CHAPTER X.

DEVELOPMENT.

SPECIAL REFERENCES.

KATHKE. Zur Entwickelungsgesch. der Blatta yermanica. Meckel's Arch, of
Anat. n. Phys., Bd. VI. (1832).

BALFOUR. Comparative Embryology, 2 vols. (1880-1).

GRABER. Insekten, Vol. II. (1879).

LUBBOCK. Origin and Metamorphoses of Insects (1874).

KOWALEWSKY. Embryol. Stuclien an Wiirmern u. Arthropoden. Mem. Ac. Petersb.
Ser. VII., Vol. XVI. (1871).

WEISMANN. Entw. der Dipteren. Zeits. f. wiss. Zool., Bde. XIII., XIV. (1SG3-4).

METSCHNIKOFF. Embryol. Studien. an Insecten. Ib., Bd. XVI. (18G6).

BiiTSCHLi. Entwicklungsgeschichte der Biene. Ib., Bd. XX. (1870).

BOBRETZKY. Bildung d. Blastoderms u. d. Keimbliitter bei den Insecten. Ib.,
Bd. XXXI. (1878).

NUSBAUXI. Rozwoj przewodow organow pteiowych u owadow (Polish). Kosmos.
(1884). [Development of Sexual Outlets in Insects.]

— Struna i struna Leydig'a u owadow (Polish). Kosmos (1886). [Chorda
and Leydig's chorda in Insects.]

The Embryonic Development of the Cockroach*

BY JOSEPH NUSBAUM, MAGISTER OF ZOOLOGY, WARSAW.

THE development of the Cockroach is by no means an easy
study. It costs some pains to find an accessible place in which
the females regularly lay their eggs, and the opaque capsule
renders it hard to tell in what stage of growth the contained
embryos will be found. Accordingly, though the development
of the Cockroach has lately attracted some observers, the

* In the following description it is to be understood that the observations have
been made upon Blatta germanica, except where P. orientalis is expressly named.

182 THE COCKROACH:

inexperienced embryologist will find it more profitable to
examine the eggs of Bees, of Aphides, or of such Diptera as lay
their eggs in water.

The Cockroach is developed, like most animals, from fertilised
eggs.* The eggs of various animals differ much in size and
form, but always contain a formative plasma or egg-
protoplasm, a germinal vesicle (nucleus), and a germinal
spot (nucleolm). Besides these essential parts, eggs also always
contain a greater or less quantity of food-yolk, which serves
for the supply of the developing embryo. The quantity of
this yolk may be small, and its granules are then uniformly
dispersed through the egg-protoplasm ; or very considerable,
in which case the protoplasm and yolk become more or less
sharply defined. Eggs of the first kind are known as holoblastic,
those of the second kind as meroblastic, names suggested by the
complete or partial segmentation which these kinds of eggs
respectively undergo. When the food-yolk is very abundant it
does not at first (and in some cases does not at any time)
exhibit the phenomena of growth, such as cell-division. If, on
the other hand, the yolk is scanty and evenly dispersed through
the egg-protoplasm, the segmentation proceeds regularly and
completely. The eggs of Arthropoda, including those of the
Cockroach, are meroblastic.

The eggs of the Cockroach (P. orientals) are enclosed (see
p. 23) sixteen together in stout capsules of horny consistence.
They are adapted to the form of the capsule, laterally com-
pressed, convex on the outer, and concave on the inner side.
The ventral surface of the embryo lies towards the inner,
concave surface of the egg. Each egg is provided with a very
thin brownish shell (chorion), whose surface is ornamented with
small six-sided projections. In young eggs, still enclosed within
the ovary, the nucleus (germinal vesicle) and nucleolus (germinal
spot) can be plainly seen, but by the time they are ready for
deposition within the capsule, so large a quantity of food-yolk,
at first finely — afterwards coarsely — granular, accumulates
within them, that the germinal vesicle and spot cease to be
visible.

* Fertilisation consists essentially in the union of an egg-nucleus (female nucleus)
with a sperm-nucleus (male nucleus). From this union the first segmentation-nucleus
is derived.

DEVELOPMENT.

183

Since the yolk of the newty-laid egg of the Cockroach is of
a consistence extremely unfavourable to hardening and micro-
scopic investigation, I have not been able to obtain transverse
sections of the germinal vesicle, nor to study the mode of its
division (segmentation). If, however, we may judge from
what other observers have found in the eggs of Insects more
suitable for investigation than those of the Cockroach, we shall
be led to conclude that a germinal vesicle, with a germinal spot
surrounded by a thin layer of protoplasm, lies within the nutri-
tive yolk of the Cockroach egg. From this protoplasm all the
cells of the embryo are derived.

The germinal vesicle, together with the surrounding proto-
plasm, undergoes a process of division or segmentation. Some
of the cells thus formed travel towards the surface of the egg
to form a thin laver of flattened cells investing the volk, the

*/ o %j

so-called blastoderm, while others remain scattered through the
yolk, and constitute the yolk-cells (fig. 107).

On the future ventral side of the embryo (and therefore on
the concave surface of the egg) the cells of the blastoderm
become columnar, and here is formed the so-called ventral
plate, the first indication of the embryo. This is a long narrow
flattened structure (fig. 104). It is wider in front where the head

LIBRARY ~

I •~*>

Fig. 104. — Ventral Plate of Blatta germanica, with developing appendages, seen

from below, x 20.

segment is situated ; further back it becomes divided by manv

*- •/

transverse lines into the primitive segments. The total number
of segments in the ventral plate of Insects is usually seventeen.*

* Balfour, Embryology, Vol. I., p. 337.

184

THE COCKROACH :

Indications of the appendages appear very early. They give
rise to an unpaired labrum, paired antennoc, mandibles, and
maxilla) (two pairs). The first and second pair of maxillae have
originally, according to Patten,* two and three branches res-
pectively. Behind the mouth-parts are found three rudimentary
legs. Upon all the abdominal segments, according to Patten,
rudimentary limbs are formed ; but these soon disappear, except
one pair, which persists for a time in the form of a knobbed stalk ;

Fig. 105. — Ventral Plate of B. germanica, side view. X 20.

subsequently this, too, completely disappears. Three or four of
the hindmost segments curve under the ventral surface of the
embryo, and apparently (?) give rise to the modified segments
and appendages of the extremity of the abdomen (fig. 105). The
ventral plate lies at first directly beneath the egg membrane
(chorion), but afterwards becomes sunk in the yolk, so that a

Fig. 106. — Diagram to illustrate the formations of the Embi-yonic Membranes.
A, amnion ; S, serous envelope ; B, blastoderm.

portion of the yolk makes its way between the ventral plate
and the chorion. Whilst this portion of the yolk is perfectly
homogeneous, the remainder, placed internally to it, becomes
coarsely granular, and encloses many roundish cavities and
* Q. J. Micr. Sci., Vol. XXIV., page 596 (1884).

DEVELOPMENT.

185

yolk-cells. The middle region of the body is more deeply sunk
in the yolk than the two ends, and the embryo thus assumes a
curved position (fig. 105).

This curvature of the embryo is closely connected with the
formation of the embryonic membranes. On either side of the
ventral plate a fold of the blastoderm arises, and these folds
grow towards each other beneath the chorion. Ultimately they
meet along the middle line of the ventral plate (fig. 106),
and thus form a double investment, the outer layer being the
serous envelope, the inner the amnion. Between the two the
yolk passes in, as has been explained above (fig. 107).

Fig. 107. — Transverse section through young Embryo of B. f/ermanica.
E, epiblast ; HI, mesoblast ; F, yolk-cells.

At the same time that the embryonic membranes are forming

v O '

the embryonic layers make their appearance. The ventral
plate, which was originally one-layered, forms the epillast or
outer layer of the embryo, and from this are subsequently
derived the middle layer (mesoblast} and the deep laver
(hypoblast).

186

THE COCKROACH :

As to the origin of the mesoblast most observers have found*

that a long groove (the germinal groove] appears in the middle
line of the ventral plate (fig. 108), which bulges into the

Fig. 108. — Diagram to illustrate the formation of the Germinal Layers.

E, epiblast ; M, mesoblast.

yolk, gradually detaches itself from the epiblast, and completes
itself into a tube. The lumen of this tube soon becomes filled
with cells, and the solid cellular mass thus formed divides into
two longitudinal tracts, which lie right and left of the middle
line of the ventral plate beneath the epiblast, and are known as
the mesoblastic bands. In the Cockroach I was able to satisfy
myself that in this Insect also, the mesoblast, in all probability,
arises by the formation and closure of a similar groove of the
epiblast. M (fig. 108) represents the stage in which the lumen
of the groove has disappeared, and the mesoblast forms a solid
cellular mass.

The origin of the hypoblast in Insects has not as yet been
clearly determined. Two quite different views on this subject
have found support. Some observers (Bobretsky, Graber, and
others) maintain that the hypoblast originates in the }7olk-cells,
which form a superficial layer investing the rest of the yolk.
Others (especially Kowalewskyf ) believe that the process is
altogether different. According to the latest observations of
the eminent embryologist just named, upon the development of
the MuscidcB, the germinal groove gives rise, not only to the

* Kowalewsky in Hydrophilus, Graber in Musca and Lina, Patten in Phryganidce,
myself in Meloe, &c.

t Biolog. Centrablatt. Bd. VI., No. 2 (1886).

DEVELOPMENT. 187

two mesoblastic bands, but also, in its central region, to the
hypoblast. This makes its appearance, however, not as a
continuous layer, but as two hourglass-shaped rudiments, one at
the anterior, the other at the posterior end of the ventral plate.
These rudiments have their convex ends directed away from
each other, while their edges are approximated and gradually
meet so as to form a continuous hypoblast beneath the meso-
blast. Although I have not been able completely to satisfy
myself as to the mode of formation of the hypoblast in the
Cockroach, I have observed stages of development which lead
me to suppose that it proceeds in this Insect in a manner
similar to that observed by Kowalewsky in Muscidce. The
hourglass-shaped rudiments of the hypoblast become pushed
upwards by those foldings-in of the epiblast which form
towards the anterior and posterior ends of the embryo, and give
rise to the stomodceum and proctodocum.*

The stage of development in which the germinal groove
appears, by the folding inwards of the epiblast, has been
observed in many other animals, and is known as the Gastroca-
stage. In all higher types (Vertebrates, the higher Worms,
Arthropoda, Echinodermata) the mesoblast and hypoblast are
formed in the folded-in part of the Gastraea in a manner
similar to that observed in Insects.

The yolk-cells, which some observers have supposed to form
the hypoblast, are believed by Kowalewsky to have no other
function except that of the disintegration and solution of the
yolk. I can, however, with confidence affirm that in the Cock-
roach these cells take part in the formation of permanent
tissues (see below).

Each of the two mesoblastic bands which lie right and left of
the germinal groove divides into many successive somites, and
each of these becomes hollow. Every such somite consists of

an inner (dorsal) one-layered and an outer (ventral) many-
layered wall, the latter being in contact with the epiblast. The
cavities of all the somites unite to form a common cavity, the
coelom or perivisceral space of the Cockroach. The ccelorn, like
the cavities in which it originates, is bounded by two layers of
mesoblast — an inner, the so-called sp/auc/tnic or visceral layer,

* These terms are explained on p. 115.

188

THE COCKROACH

which lies on the outer side of the hypoblast, and an outer
somatic or parietal layer, beneath the epiblast. There are
accordingly four layers in the Cockroach-embryo — viz., (1) epi-
bfast, from which the integument and nervous system are
developed ; (2) somatic layer of mesoblast, mainly converted into
the muscles of the body-wall ; (3) splanchnic layer of mesoblast,
yielding the muscular coat of the alimentary canal ; and (4)
hypoblast, yielding the epithelium of the mesenteron.

Scattered yolk-cells associate themselves with the mesoblast
cells, so that the constituents of the mesoblast have a two-fold
origin. Fig. 109 shows that the yolk-cells are large, finely

Fig. 109. — Transverse sections of Embryo of B. yermanica, with rudimentary nervous
system (Oc. 4, Obj. D.D. Zeiss). N, nervous system ; M, mesoblastic somites.

granular, and provided with many (3-6) nuclei and nucleoli.
They send out many branching protoplasmic threads, which
connect the different cells together, and thus form a cellular
network. Certain cells separate themselves from the rest, apply
themselves to the walls of the somites, and form a provisional

DEVELOPMENT.

189

diaphragm (fig. 110, D] consisting of a layer of flattened cells ;*
other cells (fig. 109) pass into and through the walls of the
somites, and reach their central cavity, where they increase in
number and blend with the mesoblast cells. What finally
becomes of them I cannot say ; perhaps they form the fat-body.

Fig. 110. — Transverse section through ventral region of Embryo of B. germanica. The
nerve-cord has by this time detached itself from the epiblast, E. D is the temporary
diaphragm ; Ch, temporary cellular band, from which the neurilemma proceeds ;
Ap, appendages in section; M, mesoblast; N, nerve-cord. (Oc. 4. Obj. BB.
Zeiss).

The ventral plate occupies, as I have explained, the future
ventral surface of the Insect, and here only at first both the
embryonic membranes are to be met with. On the sides and
above the yolk is invested by the serous envelope alone. The
ventral plate, however, gradually extends upwards upon the
sides of the egg, in the directions of the arrows (fig. 107), and
finally closes upon the dorsal surface of the embryo, so as com-
pletely to invest the whole yolk. Every segment of the
embryo shows at a certain stage numerous clusters of spherical
granules, which according to Patten (loc. cit.) are composed of
urates (fig. Ill, 8).

* Cf. Korotneff, Embryol. der Gryllotalpa. Zeits. f. wiss. Zool. (1885).

190

THE COCKROACH I

We shall now proceed to consider the development of the
several organs of the Cockroach.

Nervous System. — Along the middle line of the whole ventral
surface there is formed a somewhat deep groove-like infolding
of the epiblast, bounded on either side by paired solid thicken-
ings, which detach themselves from the epiblast (fig. 110, N} and
constitute the double nervous chain. In many other Insects a
median cord (from which are derived the transverse intergan-
srlionic commissures) forms along the bottom of the nervous

o / o

fold. This secondary median fold is very inconspicuous and

Fig. 111. — Transverse section of older Embryo of B. yermanica (abdomen). E. Epi-
blast ; H, kypoblast ; Ht, heart ; Gf, reproductive organs ; S, spherical granules.

slightly developed in the Cockroach, so that the transverse
commissures between the developing ganglia are mainly con-
tributed by the cellular substance of the lateral nervous band.
The brain is formed out of two epiblastic thickenings which
occupy shallow depressions. The so-called inner neurilemma,
which surrounds the ventral nerve-cord, is developed as follows: —
Along the ventral nerve- cord, and between its lateral halves,
a small solid cellular band (fig. 110, C/i) is developed out of the
mesoblastic diaphragm described above. This grows round
the ventral nerve-cord on all sides (fig. 112, JV'), passing also
inwards between the central fibrillar tract and the outer

DEVELOPMENT.

191

cellular layer, and thus forming the thin membrane which
invests the central nervous mass (fig. 112, JV"). The above-
mentioned solid mesoblastic band, which exists for a very
short time only, may perhaps be homologised with the
chorda dorsalis of Vertebrates, and the chorda of the higher

Fig. 112. — Transverse section of Nerve-cord of Embryo of B. germanica (Oc. 4, Obj.
D.D. Zeiss). (7, cellular layer; F, fibrillar substance ( jjunkt-substance of
Leydig) ; Ch, cellular band ; Nl Nn inner and outer neurilemma.

AVorms, since in these types also the chorda forms a solid
cellular band of meso-hypoblastic origin, lying between the
nervous system and the hypoblast. The peripheral nerves arise
as direct prolongations of the fibrillar substance of the nerve-
cord.

Fig. 113. — Alimentary Canal of Embryo of B. germanica. Copied from llathke,
loc. cit., but differently lettered. st, stomodseum, already divided into
oasophagus, crop, and gizzard ; m, mesenteron ; pr, proctodseum, with Malpighian.
tubules (removed on the right side). X 12.

192 THE COCKROACH:

Alimentary Canal. — The epithelium of the mesenteron is
formed out of the hypoblast, whose cells assume a cubical form
and gradually absorb the yolk. The epithelium of the stomo-
daourn and proctodacum is derived, however, from two epiblastic
involutions at the fore and hind ends of the embryo. The
muscular coat of the alimentary canal is contributed by the
splanchnic layer of the mesoblast. The mesenteron in an
early stage of development appears as an oval sac of greenish
colour (fig. 113), faintly seen through the body- wall. The csecal
tubes are extensions of the mesenteron, the Malpighian tubules
of the proctodcToum. The epiblastic invaginations may be
recognised in all stages of growth by their chitinous lining
and layer of chitinogenous cells, continuous with the similar
layers in the external integument,

Tracheal System. — Tubular infoldings of the epiblast, forming
at regular intervals along the sides of the embryo and project-
ing into the somatic mesoblast, give rise to the paired tracheal
tubes, which are at first simple and distinct from one another.*

Heart. — The wall of the heart in Insects is of mesoblastic
origin, and develops from paired rudiments derived from that
peripheral part of each mesoblastic band which unites the
somatic to the splanchnic layer. In this layer two lateral
semi-cylindrical rudiments appear, which, as the mesoblastic
bands meet on the dorsal surface of the embryo, are brought
into contact and unite to form the heart (fig. 111). The heart is
therefore hollow from the first, its cavity not being constricted
off from the permanent perivisceral space enclosed by the
mesoblast, but being a vestige of the primitive embryonic
blastoco3l, which is bounded by the epiblast, as well as by the
two other embryonic layers. Such a mode of the development
of the heart was observed by Biitschli in the Bee, and by
Korotneff in the Mole Cricket. I am convinced, from my own
observations, that the heart of the Cockroach originates in this
way, though it is to be observed that, in consequence of

* In Gryllotalpa (Dolirn), as in Spiders, some Myriopods and Peripatus (Moseley,
Phil. Trans., 1874), each stigma, with its branches, constitutes throughout life a
separate system. The salivary glands arise in the same way, not, like the salivary
glands of Vertebrates, as extensions of the alimentary canal, but as independent
pits opening behind the mouth. Both the tracheal and the salivary passages are
believed to be special modifications of cutaneous glands (Moseley).

DEVELOPMENT.

193

Patten's results,* the question requires further investigation.
According to Patten the mesoblastic layers of the embryo

C_J V &

pulsate rhythmically long before the formation of the heart.
Patten also states that the blood-corpuscles are partially derived
from the wall of the heart.

Reproductive Organs. — In P. orientaHs the reproductive organs
are developed as follows : — The reproductive glands have a
mesoblastic origin. The immature ovaries and testes take the
form of elongate oval bodies, which prolong themselves back-
wards into a long thin thread-like cord or ligament (figs.
114, 115). These lie in the perivisceral space, between the

Fig. 114.— Young Ovary of B, germanica.
(Oc. 2, Ob. DD, Zeiss.)

Fig. 115. — Young Testis of B. germanica.
(Oc. 2, Ob. DD, Zeiss.)

somatic and splanchnic layers of the mesoblast, and on the
sides of the abdomen. The glands divide tolerably early into
chambers, which have, however, a communicating passage (figs.

* Loc. cit.

194

THE COCKROACH :

114, 115). From their backward-directed prolongations arises
the epithelium of the vasa deferentia and oviducts. All other
parts of the reproductive ducts are developed out of tegumen-
tary thickenings of the ventral surface in the last abdominal
segment, and the last but one. These thickenings are at first
paired,* but afterwards blend to form single organs (fig. 118).
Within the tegumentary thickenings just described, there

Figs. 116, 117, 118.— Three stages of development of teguuieutary portion of Male
Sexual Organs of P. orientalis. (Oc. 1, Ob. B B, Zeiss.) V D, vas deferens ;
V S, vesicula seminalis ; D, ductus ejaculatorius ; P, p, penis and its lateral
appendages.

appear in the male Cockroach two anterior closed cavities
which unite to form the single cavity of the permanent mush-
room-shaped body (vesicula seminalis). A. posterior cavity
becomes specialised as the ductus ejaculatorius, while the hind-
most part of the thickening, which is at first double, afterwards
by coalescence single, forms the penis (figs. 117, 118). The

* This arrangement persists only in Ephemeridcv among Insects (Palmen, Ueb.
paarigen Ausfiihrungsgange der Geschlechtsorgane bei Insekten, 1884).

DEVELOPMENT. 195

accessory reproductive glands have also a tegumentary origin.
In the female Cockroach the chitinogenous epithelium of the
integument gives rise to the uterus, vagina,* and accessory
glands, the muscular and connective tissue layers of the sexual
apparatus being formed out of loose mesoblastic cells. f

JOSEPH

Post- embryonic Development.

At the time of hatching the Cockroach resembles its parent
in all essentials, the wings being the only organs which are
developed subsequently, not as entirely new parts, but as exten-
sions of the lateral edges of the thoracic terga. The mode of
life of the young Cockroach is like that of the adult, and
development may be said to be direct, or with only a trifling
amount of metamorphosis. In the Thysanura even this
small post- embryonic change ceases to appear, and the Insect,
when it leaves the egg, differs from its parent only in size. It
is probable that development without metamorphosis was once
the rule among Insects. At present such is by no means the
case. Insects furnish the most familiar and striking, though,
as will appear by-and-by, not the most typical examples of
development with metamorphosis. In many text-books the
quiescent pupa and the winged imago are not unnaturally
described as normal stages, which are exceptionally wanting in
Orthoptera, Hemiptera, Thysanura, and other " ametabolous '
Insects. It is, however, really the " holometabolous ' Insects
undergoing what is called " complete metamorphosis,"
which are exceptional, deviating not only from such little-
specialised orders as Thysanura and Orthoptera, but from nearly
all animals which exhibit a marked degree of metamorphosis.
"We shall endeavour to make good this statement, and to show
that the Cockroach is normal in its absence of conspicuous
post-embryonic change, while the Butterfly, Bee, Beetle, and
Gnat are peculiar even among metamorphic animals.

* Genital pouch of the preceding description.

f Indications, which we have not found time to work out, lead us to think that
the development of the specially modified segments and appendages in the male and
female Cockroach needs re -examination. We hope to treat this subject separately
on a future occasion. — L. C. M. and A. D.

10G THE COCKROACH:

Animal Metamorphoses.

To investigate the causes of metamorphosis, let us select from
the same sub-kingdom two animals as unlike as possible
with respect to the amount of post-embryonic change to which
they are subject. We can find no better examples than
Amphioxus and the Chick.

The newly-hatched Amphioxus is a small, two- layered,
hollow sac, which moves through the sea by the play of cilia
which project everywhere from its outer surface. It is a
Grastmca, a little simpler than the Hydra, and far simpler than
a Jelly-fish. As yet it possesses no nervous system, heart,
respiratory organs, or skeleton. The most expert zoologist,
ignorant of its life-history, could not determine its zoological
position. He would most likely guess that it would turn either
into a polyp or a worm.

The Chick, on the other hand, at the tenth day of incubation,
is already a Bird, with feathers, wings, and beak. When it
chips the shell it is a young fowl. It has the skull, the skele-
ton, the toes, and the bill characteristic of its kind, and no
child would hesitate to call it a young Bird.

Amphioxus is, therefore, a Vertebrate (if for shortness we
may so name a creature without vertebrae, brain, or skull),
which develops with metamorphosis, being at first altogether
unlike its parent. The Chick is a Vertebrate which develops
directly, without metamorphosis. Let us now ask what other
peculiarities go with this difference in mode of development.

Amphioxus produces many small eggs (T^ mm. in diameter)
without distinct yolk, and consequently segmenting regularly.
The adult is of small size (2 to 3 in. long), far beneath the
Chick in zoological rank, and of marine habitat.

The Fowl lays one egg at once, which is of enormous size
and provided with abundant yolk, hence undergoing partial
segmentation. The Fowl is much bigger than Amphioxus,
much higher in the animal scale, and of terrestrial habitat.

Which of the peculiarities thus associated governs the rest ?
Is it the number or size of the eggs ? Or the size, zoological
rank, or habitat of the adult ? The question cannot be answered
without a wider collection of examples. Let us run over the

DEVELOPMENT. 197

great divisions of the Animal Kingdom, and collect all the facts
which seem to be significant. We may omit the Protozoa,
which never develop multicellular tissues, and in which seg-
mentation and all subsequent development are therefore
absent.

PORIFERA (Sponges). — Nearly all marine and undergoing
metamorphosis, the larva being wholly or partial!}^ ciliated.

CCELENTERATES undergo metamorphosis, the immediate pro-
duct of the ovum being nearly always ap/amifa, or two-layered
hollow sac, usually devoid of a mouth, arid moving about by
external cilia. In many Coelenterates the complicated process
of development known as Alternation of Generations occurs.
The sedentary Anemones pass through a planula stage, but
within the body of the parent. Among the few Ccelenterates
which have no free planula stage is the one truly fluviatile
genus — Hydra.

WORMS are remarkable for the difference between closely
allied forms with respect to the presence or absence of meta-
morphosis. The iion-paras4tic freshwater and terrestrial
Worms, however (e.g., Earthworms, Leeches, all freshwater
Dendrocoela, and Rhabdocoela), do not undergo metamorphosis.
In the parasitic forms complicated metamorphosis is common,
and may be explained by the extraordinary difficulties often
encountered in gaining access to the body of a new host.

All POLYZOA are aquatic (fluviatile or marine), and all produce
ciliated embryos, unlike the parent.

BRACHIOPODA are all marine, and produce ciliated embryos.

ECHINODERMS usually undergo striking metamorphosis, but
certain viviparous or marsupial forms develop directly. There
are no fluviatile or terrestrial Echinoderms.

LAMELLIBRANCHIATE MOLLUSCA have peculiar locomotive
larvae, provided with a ring of cilia, and usually with a long
vibratile lash. These temporary organs are reduced or sup-
pressed in the freshwater forms. There are no terrestrial
Lamellibranchs.

SNAILS have also a temporary ciliated band, but in the fresh-
water species it is slightly developed (Limnceus), and it is totally
wanting in the terrestrial HeUcidce.

198 THE COCKROACH :

CEPHALOPODA, which are all marine, have no ciliated band,
and the post-embryonic changes do not amount to metamor-
phosis. There is usually a much larger yolk-sac than in other
Mollusca.

CRUSTACEA usually pass through well-marked phases. Pcneus
presents five stages of growth (including the adult), the earlier
being common to many lower Crustacea. The Crab passes
through three, beginning with the third of Peneus ; the Lobster
through two ; while the freshwater Crayfish, when hatched, is
already in the fifth and last.

FISHES seldom undergo any post-embryonic change amount-
ing to metamorphosis. Ampliioxus (if Amphioxm be indeed a
fish) is the only well-marked case.

AMPHIBIA develop without conspicuous metamorphosis, except
in the case of the Frogs and Toads (Anura), which begin life
as aquatic, tailed, gill- bearing, and footless tadpoles.

REPTILES, BIRDS, and MAMMALS do not undergo transformation.

This survey, hasty as it necessarily is, shows that habitat is a
material circumstance. Larval stages are apt to be suppressed
in fluviatile and terrestrial forms. Further, it would seem that
zoological rank is not without influence. Metamorphosis is
absent in Cephalopoda, the highest class of Mollusca, and in all
but the lowest Vertebrates, while it is almost universal in
Coelenterates, Echinoclerms, and Lamellibranchs.

It has often been remarked that the quantity of food-yolk
indicates the course of development. If a large store of food
has been laid up for the young animal, it can continue its
growth without any effort of its own, and it leaves the egg well
equipped for the battle of life. Where there is little or no
yolk, the embryo is turned out in an ill-furnished condition to
seek its own food. This early liberation implies metamorphosis,
for the small and feeble larva must make use of temporary
organs. Some very simple locomotive appendages are almost
universally needed, to enable it to get away from the place of its
birth, which is usually stocked with as much life as it can support.

Some animals, therefore, are like well-to-do people, who can
provide their children with food, clothes, schooling, and pocket-
money. Their fortunate offspring grow at ease, and are not

DEVELOPMENT. 199

driven to premature exercise of their limbs or wits. Others are
like starving families, which are forced to send their children
to sell matches or newspapers in the streets. It is a question of
the amount of capital or accumulated food which is at command.

The connection between zoological rank and the absence of
metamorphosis is also explained by what we see among men.
High zoological position ordinarily implies strength or intelli-
gence, and the strong and knowing can do better for their
offspring than the puny and sluggish. It does not cost a Shark
or a quadruped too much to hatch its young in its own body,
while Spiders and Earwigs,* which are among the highest
Invertebrates, defend their progeny, as do Mammals and Birds,
the highest Vertebrates.

But what has all this to do with habitat ? Are fluviatile and
terrestrial animals, as a rule, better off than marine animals ?
Possibly they are. In the confined and isolated fresh waters at

«/ V

least, the struggle for existence is undoubtedly less severe than

O O u

* It may be useful to point out the following examples of parental care among
animals in which, as a rule, the eggs are left to take care of themselves. It will be
found that in general this instinct is associated with high zoological rank (best
exemplified by Mammals and Birds), land or freshwater habitat, reduced number of
eggs, and direct development.

AMPHIBIA. — The eggs are sometimes hatched by the male (Alytes obsletr leans,
Rhinoderma Dancinii), or placed by the male in pouches on the back of the
female (Ptpa dorsiyera, Notodelphis ovifera, Nototrema marsupiatum), or
carried during hatching by the female (Polypedates reticulatus) .

FISHES. — The Stickleback and others build nests. Of eleven genera of nest-
building Fishes, eight are freshwater. The number of eggs is unusually small.
Many Siluroids have the eggs hatched in the mouth of the males, a few under
the belly of the female. The species are both marine and freshwater, the eggs
few and large. Lophobranchiate fishes usually have the eggs hatched by the male.
They are marine ; the eggs few and large. Many sharks hatch their eggs, which
are very few, within the body. Mustelus Icevis has a placenta, formed out of the
yolk-sac.

INSECTS. — De Geer has described the incubation of the Earwig, and the care of
the brood by the female. The cases of the social Hymenoptera, &c., are
universally known.

SPIDERS. — The care of the female spider for her eggs is well known.

CBUSTACEANS. — The Crayfish hatches and subsequently protects her young. Mysis,
Diastylis (Cuma), and some Isopods hatch their eggs. Gammarus locusta is
followed about by her brood, which shelter beneath her when alarmed. Podocerus
capillatus builds a nest among corallines. Several of the CapreUidce hatch or
otherwise protect their young. All these, except the Crayfish, are marine ; the
eggs commonly fewer than usual.

ECHINODERMS. — Many cases of "marsupial development" have been recorded
in the species of the Southern seas. Here development, conti ary to the rule in
Echinodermata, is direct.

200 THE COCKROACH :

in the waters of the sea. This is shown by the slow rate of
change in freshwater types. Many of our genera of land and
freshwater shells date back at least as far as to Purbeck and
Wealden times, while our common pond-mussel is represented
in the Coal Measures. The comparative security of fresh
waters is probably the reason why so many marine fishes enter
rivers to spawn.

More important, and less open to question, is the direct action
of the sphere of life. The cheap method of turning the
embryo out to shift for itself can seldom be practised with
success on land. But in water floating is easy, and swimming
not difficult. A very slightly-built larva can move about by
means of cilia, and a whole brood can disperse far and wide in
search of food, while still in a mere planula condition — hollow
sacs, without mouth, nerves, or sense-organs. Afterwards the
little locomotive larva settles down, opens a mouth, and begins
to feed. Nearly the whole of its development is carried on at
its own charge.

The extra risks to which marine animals are exposed also
tell in favour of transformation, for they are met by an increase
in the number of ova. Marine species commonly lay more eggs
than freshwater animals of like habits. The Cod is said to
produce nine million eggs ; the Salmon from twenty to thirty
thousand ; the Stickleback only about one hundred, which are
guarded during hatching by the male. The Siluroid fish, Ariits,
lays a very few eggs, as big as small cherries, which the male
carries about in his mouth.

Without laying stress upon such figures as these, which
cannot be impartially selected, we can safely affirm that marine
forms are commonly far more prolific than their freshwater
allies. But high numbers increase the difficulty of providing
yolk for each, and thus tend to early exclusion, and subsequent
transformation. We may rationally connect marine habitat
with small eggs, poorly supplied with yolk, segmenting regu-
larly, and producing larva which develop with metamorphosis.

In fresh waters dispersal can seldom be very effective. The
area is usually small, and communicates with other freshwater
basins only through the sea. Migration to a considerable distance
is usually impossible, and migration to a trifling distance use-

DEVELOPMENT.

less. Moreover, competition is not too severe to prevent some
accumulation of food by the parent on behalf of the family.

On land the conditions are still less favourable to larval
transformation. Very early migration is altogether impossible.
Any kind of locomotion by land implies muscles of complicated
arrangement, and, as a rule, there must be some sort of skeleton
to support the weight of the body. The larva, if turned out in
a Gastraea condition would simply perish without a struggle.*
Nor is great precocity needful. The terrestrial animal is com-
monly of complicated structure, active, and well furnished with
means of information. It can lay-by for its offspring, and
nourish them within its own body, or at least by food stored up
in the egg.

The influence of habitat upon development may be recapitu-
lated as follows : —

MARINE HABITAT. — Eggs many. Yolk small. Segmentation
often regular. Young hatched early. Development with
metamorphosis. [The most conspicuous exceptions are Cephalo-
poda and marine Yertebrata.]

FLUVIATILE HABITAT. — Eggs fewer. Yolk larger. Seg-
mentation often unequal. Young hatched later. Development
direct, or with late metamorphosis only. [The most obvious ex-
ceptions are Frogs and Toads, which developwith metamorphosis.]

TERRESTRIAL HABITAT. — Eggs few. Yolk large [except
where the young are supplied by maternal blood]. Segmenta-
tion often partial. Young hatched late. Development without
metamorphosis. [An exception is found in Insects, which
usually exhibit conspicuous metamorphosis, though the yolk is
large, and the type of segmentation partial or unequal.]

Let us now take up the exceptions, and see whether these are
capable of satisfactory explanation.

1. — Cephalopoda and marine Yertebrates, unlike other in-
habitants of the sea, develop without metamorphosis. But
these are large animals of relatively high intelligence, well able
to feed and protect their young until development is completely
accomplished.

* The minute and early larvae of Tcenia and Distomum may appear to contradict
this statement. They really inhabit the film of water which spreads over wet grass,
though they are capable of enduring dry conditions for a short time, like Rotifers and
many Infusoria.

202 THE COCKROACH :

2. — Frogs and Toads, unlike other fluviatile animals, develop
with metamorphosis. The last and most conspicuous change,
however, from the gill-bearing and tailed tadpole to the air-
breathing and tailless frog, hardly belongs to the ordinary
period of embryonic development. When the tadpole has four
limbs and a long tail it has already reached the point at which
the more primitive Amphibia (Menopoma, Proteus, &c.) become
sexually mature. The loss of the tail, the lengthening of the
hind limbs, and the complete adaptation to pulmonary respira-
tion, relate to the mode of dispersal of the adult. Cut off from
early dispersal by the isolation of their breeding-places and the
difficulty of land migration, Frogs migrate from pool to pool as
full-grown animals. The eggs are thus laid in new sites, and
very small basins — ditches and pools which dry up in summer
— can be used for spawning. To this peculiar facility in finding
new spawning grounds the Anura no doubt owe their success in
life, of which the vast number of nearly-allied species furnishes
an incontrovertible proof. But the adaptation to terrestrial
locomotion necessarily comes late in life, after the normal and
primitive adult Amphibian condition has been attained. It is
by a secondary adult metamorphosis that the aquatic tadpole
turns into the land-traversing frog. The change is not fairly
comparable to any process of development by which other
animals gain the adult structure characteristic of their class
and order, but (in respect of the time of its occurrence)
resembles the late assumption of secondary sexual characters,
such as the antlers of the stag, or the train of the
peacock.

3. — Lastly, we come to the exceptional case of Insects which,
unlike other terrestrial animals, develop with metamorphosis.
The Anurous Amphibia have prepared us to recognise this too
as a case of secondary adult (post-embryonic) metamorphosis.
Thysanuran or Orthopterous larva) cannot differ very widely
from the adult form of primitive Insects. From wingless,
hexapod Insects, like Cockroach larvae in all essentials of
external form, have been derived, on the one hand, the winged
imago, adapted in the more specialised orders to a brief pairing
season exclusively spent in migration and propagation ; on the
other hand, the footless maggot or quiescent pupa.

DEVELOPMENT. 203

Insects, like Frogs, disperse as adults, because of the
difficulty of the medium, aerial locomotion being even more
difficult than locomotion by land, and implying the highest
muscular and respiratory efficiency. The flying state is attained
by a late metamorphosis, which has not yet become universal in
the class, while it is not found in other Tracheates at all.
Peripatus, Scorpions, and Myriopods become sexually mature
when they reach the stage which corresponds to the ordinary
less-modified Insect-nymph, with segmented body, walking-
legs, and mouth-parts resembling those of the parent.*

The Caterpillar is not, as Harveyf maintained, a kind of
walking egg ; it is rather the primitive adult Tracheate modified
in accordance with its own special needs. It may be sexually
immature, imperfect, destined to attain more elaborate develop-
ment in a following stage, but it nevertheless marks the stage
in which the remote Tracheate ancestor attained complete
maturity. Where it differs from the primitive form, hatched
with all the characters of the adult, the changes are adaptive
and secondar.

The Genealogy of Insects.

To construct from embryological and other data a chart of
the descent of Insects, and of the different orders within the

* It is possible that the curious cases of agamogenetic reproduction of the larvae
of Aphis, Cecidomyia, and Ckironomus are vestiges of the original fertility of
Insect larvre.

f "Alia vero semen adhuc imperfectum et immaturatum recludunt, incrementum
et perfectionem, sive maturitatem, soris acquisiturum ; ut plurima genera piscium,
ran*, item mollia, crustata, testacea, et cochleae : quorum ova primum exposita sunt,
veluti origines duntaxat, inceptiones et vitelli ; qui postea albumina sibi ipsis circum
circa induunt ; tandemque alimentum sibi attrahentes, concoquentes et apponentes,
in perfectum semen atque ovum evadunt. Talia sunt insectorum semina (vermes ab
Aristotele dicta) qute initio imperfecte edita sibi victum quserunt indeque nutriuntur
et augentur, de eruca in aureliam ; de ovo imperfecto in perfectum ovum et semen."
— De generatione, Exc. II., p. 183 (1666). Viallanes justifies this view by applying
it to the histolysis and regeneration of the tissues in Diptera. But these remark-
able changes are surely secondary, adaptive, and peculiar, like the footless maggot
itself, whose conversion into a swift-flying imago renders necessary so complete a
reconstruction.

J The reader is recommended to refer to Fritz Miiller's Facts and Arguments for
Darwin, especially chap. xi. ; to Bal four's Embryology, Vol. II., chap, xiii.,
sect. ii. ; and to Lubbock's Origin and Metamorphoses of Insects.

204 THE COCKROACH.

class, is an attempt too hazardous for a student's text-book.*
A review of the facts of Arthropod development led Balfourf
to conclude that the whole of the Arthropoda cannot be united
in a common phylum. The Tracheata are probably "descended
from a terrestrial Annelidan type related to Peripatus.
The Crustacea, on the other hand, are clearly descended from a
Phyllopod-like ancestor, which can be in no way related to
Peripatus." The resemblances between the Arthropoda appear
therefore to be traceable to no nearer common ancestors than
some unknown Annelid, probably marine, and furnished with a
chitinous cuticle, an ccsophageal nervous ring, and perhaps with
jointed appendages. Zoological convenience must give place to
the results of embryological and historical research, and we
shall probably have to reassign the classes hitherto grouped
under the easily defined sub-kingdom of Arthropoda.

Sir John Lubbock has explained, in his very interesting
treatise on the Origin and Metamorphoses of Insects, the
reasons which lead him to conclude " that Insects generally
are descended from ancestors resembling the existing genus
Campodea [sub-order Collembola], and that these again have
arisen from others belonging to a type represented more or less
closely by the existing genus Lindia" [a non-ciliated Rotifer].

Present knowledge does not, therefore, justify a more definite
statement of the genealogy of Insects than this, that in com-
mon with Crustacea they had Annelid ancestors, and that
Lindia, Peripatus, and Campodea approximately represent three
successive stages of the descent. When we reflect that Cock-
roaches themselves reach back to the immeasurablv distant

palaeozoic epoch, we get some misty notion of the antiquity and
duration of those still remoter ages during which Tracheates,
and afterwards Insects, slowly established themselves as new
and distinct groups of animals.

'' Those who care to see a bold experiment of this kind may refer to Haeckel's
Schopfungsgeschichte.

*t* Comp. Embryology, Vol. I., p. 451.

CHAPTER XL
THE COCKROACH OF THE PAST.

BY S. H. SCUDDER, OF THE U.S. GEOLOGICAL SURVEY.

SPECIAL REFERENCES.

BEREXDT, G. C. Memoire pour servir a 1'histoire des Blattes antediluviennes
(Ann. Soc. Entom., France, V.). Paris, 1830. 8vo.

BRODIE, P. B. A History of the Fossil Insects in the Secondary Rocks of
England. London, 1845. 8vo.

GEINITZ, F. E. Die Blattinen aus der unteren Dyas von Weissig (Nova Acta.
Acad. Leop. -Carol., XLL). Halle, 1880. 4to.

GERMAR, E. F., und BEREXDT, G. C. Die im Bernstein befindlichen Hemipteren
und Orthopteven der Yorvvelt. Berlin, 1856. Fol.

GOLDENBERG, F. Zur Kenutniss der Fossilen Insekten in der Steinkohlen-
formation (Neues Jahrb. Miner). Stuttgart, 18G9. Svo.

— Fauna Sarajpontana Fossilis. Heft 1-2, Saarbriicken, 1873, 1877. 4to.

HEER, O. Ueber die fossilen Kakerlaken (Viertelj. Xaturf. Ges., Zurich, IX.).
Ziirich, 1804. Svo.

KLIVER, M. Ueber einige Blattarien . . . aus der Saarbriicker Steinkohlen-
formation (Pakeontogr. XXIX.). Cassel, 1883. 4to.

KUSTA, J. Ueber enige neue Bohmlsche Blattinen (Sitzungsb. bb'hm. Ges.
Wissensch, 1883). Prag. Svo.

SCUDDER, S. H. Palaeozoic Cockroaches (Mem. Bost. Soc. Xat. Hist., III.).
Boston, 1879. 4to.

The Species of Mylacris (Ibid). Boston, 1884. 4to.

A Review of Mesozoic Cockroaches (Ibid). Boston, 1886. 4to.

Triassic Insects from the Rocky Mountains (Anier. Journ. Sc. Arts [3],

XXV1IL). New Haven, 1884. Svo.

- Systeuiatische Uebersicht der fossilen Myriopoden, Arachuoideen und
Insekten (Zittel, Handb. Palaeont. I. Abth., Bd. II.). Miincheu, 1885. Svo.

WESTWOOD, J. O. Contributions to Fossil Entomology (Quart. Journ. Geol. Soc.,
Lond., X.). London, 1854. Svo.

LIKE all useful scavengers, the Cockroach is looked upon
nowadays as an unmitigated pest. It has, however, a certain
right to our regard, for it conies of a venerable antiquity.
Indeed, palaeontologically considered, no Insect is so interesting
as the Cockroach. Of no other type of Insects can it be said
that it occurs at every horizon where Insects have been found
in any numbers ; in no group whatever can the changes

206 THE COCKROACH

wrought by time be so carefully and completely studied as
here ; none other has furnished more important evidence con-
cerning the phylogeny of Insects. Even the oldest known air-
breathing animal has been claimed (though I think erroneously)
as a Cockroach ; yet, however that may be, it is certain that in
the most ancient deposits which have yielded any abundance of
Insect remains, the Coal Measures, they so far outnumber all
other types of Insects, that this period, as far as its hexapodal
fauna is concerned, may fairly be called the Age of Cockroaches.
And though the subsequent periods show an ever-diminishing
percentage of this family when compared with the total syn-
chronous Insect fauna, yet the existing species are counted by
hundreds, and the fecundity of some, attested by every house-
wife, may be looked upon as a sufficient explanation of the
persistence of this antique type. The Cockroach is, therefore,
a very aristocrat among Insects.

Our knowledge of its, past is derived almost entirely from its
wings ; perhaps because these organs are the farthest removed
from the nourishing fluids of the body, which on death become
one of the agents, or at least the media, of putrefaction and
consequent obliteration. At all events, whatever the cause,
these chitinous membranes, with their network of supporting
rods, and even not infrequently with the minutest reticulation
of the membrane itself, are preserved with extraordinary fidelity,
and in such abundance that, by comparison with similar parts
in existing forms, we may reach some general conclusions
concerning the life of the past of no little interest.

The first thing that would strike an observer, looking at the
ancient Cockroaches, would be their general resemblance to the
living. Excepting for their usually larger size,* were we to
have the oldest known Cockroaches in our kitchens to-day, the
householder would take no special note of them — unless, indeed,
the transparency of their wings (shortly to be mentioned) were
to give them a somewhat peculiar aspect. There would be the
same rounded pronotal shield, the same overlapping wings,
coursed bv branching: veins, the same smooth curves and oval

*/ cj

flattened form of the whole creature, and doubtless also the

* Yet noiie were so large as our largest living forms ; their average size was very
nearly that of Pcriplaneta americana.

OF THE PAST. 207

same scurrying movements. Indeed, some accurate observers —
so, I suppose, we must call them. — have failed to take note of
some important and very general distinctions between the
living and the dead. Thus Gerstaecker, in a work begun
twenty years a^o. and not vet finished, said, near its beginning,*

*; *. O ' V

"Not a single species of Insect has yet been found in the Car-
boniferous rocks which does not fall, on closer examination
(mit roller Evident), not only in an existing order, but even
almost completely in the same family as some living form, and
only presents striking distinctions when compared with the
species themselves." He further specifies the Cockroaches
described from the Coal Measures, by Germar and Goldenberg,
as agreeing in every distinguishing family characteristic with
those of the present day.

In one sense, indeed, this is true. We separate the living
Cockroaches from other kinds of Orthoptera as a " family '
group, and " Cockroaches ' have existed since the Coal
Measures at least ; yet the structure of every one of the older
types is really so peculiar that none of them can be brought
within the limits of the family as it now exists. We recognise
ours, indeed, as the direct descendants of the ancient forms, but
so changed in structure as to form a distinct group. A parallel
case is found in the Walking-sticks, and is even more obvious.
The recent researches of M. Charles Brongniart have brought
to view a whole series of forms in Carboniferous times, which
are manifestly the progenitors of living Walking-sticks, with
their remarkably long and slender stick-like body, attenuated
legs, and peculiar appendages at the tip of the abdomen. Exist-
ing forms are either wingless or else have opaque elytron-like
front wings, and very ample, gauzy, fan-like hind wings ; while
the Carboniferous species are furnished with four membranous
wings, almost precisely alike, and so utterly different from those
of existing types that, before the discovery of the bodies, these
wings were universally classed as the wings of Neuropterous
Insects (sensu Linneano). Thus Gerstaecker, in the very place
already quoted, says of these same wings, known under the
generic name Dictyoneura, that they show at least a very close
relationship to the Ephemeridce of to-day.

* Die Klassen und Ordnungen der Arthropoden. Leipzig, Svo, p. 292.

208 THE COCKROACH

One principal difference here alluded to — the exact resem-
blance, except in minor details, of the front and hind wings,
and, as consequent therewith, equal diaphaneity in both — is found
indeed in all palaeozoic insects, with exceedingly few exceptions;*
it is one of their most characteristic and pervading peculiarities.
It marks one phase of the movement in all life from homo-
geneity to heterogeneity — from the uniform to the diverse. In
the Cockroaches of to-day a few are found in which the tegmina
are nearly as diaphanous as the hind wings ; but in the great
mass the texture of the tegmina, as in Orthoptera generally
(excepting most Gryllides), is decidedly coriaceous ; and in
some, e.g., Phoraspis, the veins are nearly obliterated in the
thickness and opacity of the membrane, so as to resemble many
Coleopterous elytra.

Three principal differences have been noticed between the
ancient and modern forms of Cockroaches. Doubtless others
could be found were we able to compare the structure of all
parts of the body ; and perhaps future research and more happy
discovery may yet bring them to light ; at present, however,
we are compelled to restrict our comparisons to the wings
alone.

First, we have to remark the similarity of the front and hind
wings in the ancient types : a similarity which extends to their
general form (the extended anal area of the hind wings in
modern types being as yet only slightly differentiated) ; their
nearly equal size (a corollary, to a certain extent, of the last) ;
the general course of their neuration (true, in a limited sense
only, of modern types) ; and the complete transparency of the
front as well as of the hind wing.

Second, the same number of principal veins is developed in
the front and hind wings of ancient Cockroaches ; while in the
front wings of modern types two or more of the veins are
blended, so as to reduce the number of the principal stems
below the normal, the hind wing at the same time retaining its
original simplicity. These principal veins are six, counting the
marginal vein, which here merely thickens the anterior border,
as one ; to use the terminology of Heer, and starting from the
anterior margin, they are the marginal, mediastinal, scapular,

* A few elytra of Coleoptera are recently announced from the Silesian "culm."

OF THE PAST.

209

externomedian, internomedian, and anal The general disposition
of these veins is as follows: — The mediastinal and scapular veins,
with their branches, which are superior (i.e., part from the main
vein on the upper or anterior side), terminate upon the anterior
margin. The internomedian and anal take the opposite course,
and their branches are inferior, or, at least, directed toward the
inner margin ; while the externomedian, interposed between
these two sets, terminates at the tip of the wing, and branches
indifferentlv on either side.

£.xterno*

Fig. 119. — Schematic view of Wing of Palaeozoic Cockroach, showing the

veins and areas.

Now these veins are all present in both front and hind wings
of pakeozoic Cockroaches, and also in the hind wings of existing
species ; but in the front wings or tegmina of the latter the
number is never complete, the externomedian vein being always
amalgamated either with the scapular, or with the interno-
median, and the mediastinal frequently blended with the
scapular vein.

The hind wings are thus shown to be conservative elements
of structure, since they have preserved from the highest
antiquity both their transparency and their normal number of

210 THE COCKROACH

veins. They have retained the use to which they were first put,
and the changes that have come about, such as the wider expan-
sion of the anal area, have been in fuller development of the
same purpose ; while the front wings, in virtue of their position
in repose, have become more and more protectors of the hind
wings, and have gradually lost, in part, if not entirely, their
original use. The hind wings of existing Insects, thus pro-
tected, have given less play to selective action, and have become
to some degree interpreters for us of the more complicated
structure, the more modernised anatomy, the more varied
organisation of the front wing.

A third distinction between palaeozoic and modern Cockroaches
is found in the veinlets of the anal area. These, unlike the
branches of the other veins, do not part from the main anal
vein at various points along its course, but form a series of
semi-independent veinlets, and in palaeozoic Cockroaches take
the same general course as the main anal vein, or " anal
furrow' (the curved, deeply sunken vein that marks off the
anal area from the rest of the front wins-, both in ancient and

*-^ '

modern Cockroaches), and terminate at sub-equidistant intervals
upon the inner margin ; while in modern Cockroaches these
veins either run sub-parallel to the inner margin and terminate
on the descending portion of the anal furrow, or they form a
fusiform bundle and terminate in proximity to one another and
to the tip of the anal furrow.

These differences, which were mentioned bv Germar and

' «/

Goldenberg, and their universality pointed out in my memoir
on Palaeozoic Cockroaches,* seem to warrant our separating the
older forms from the modern as a family group, under the name
of Palmobla Harm ; this familv has been thus characterised: —

Fore wings diaphanous, generally reticulated, and nearly
symmetrical on either side of a median line. Externomedian
vein completely developed, forking in the outer half of the
wing, its branches generally occupying the apical margin ;
internomedian area broad at base (be}7ond the anal area),
rapidly tapering apically, and filled with oblique mostly parallel
veins, having nearly the same direction as the anal veinlets,
which, like them, strike the inner margin.

* Memoirs Bost. Soc. Nat. Hist., III., 23 seq. (1880).

OF THE PAST.

211

About eighty palaeozoic species have been published up to the
present time, and have been grouped in two sub-families and
thirteen genera. Besides these, Brongniart has not yet given
any hint of how many have been found at Comrnentry, a
French locality which may be expected to increase the number
largely, and about twenty undescribed species are known to me
from the American Carboniferous rocks.

The two tribes or sub-families differ in the structure of the
mediastinal vein ; in one type (Blattinarice) the branches part
from the main stem as in the other veins, at varying distances

Fig. 120. — Etoblattina mazona, Scudd. x 3. (The outline of natural size.)

Carboniferous, Illinois.

along its course (see the figure of Etoblattina) ; in the other
(Mylacridce) they spread like unequal rays of a fan from the
very base of the wing (see the figure of Mylacris). What is

212

THE COCKROACH

curious is that the latter type has been found only in the New
World, while the former is common to Europe and America.
The latter appears to be the more archaic type, since it is
probable that the primeval Insect wing was broad at the base,
as is the general rule in palaeozoic wings, and had the veins
somewhat symmetrically disposed on either side of a middle
line ; in this case the mediastinal and anal areas would be
somewhat similar and more or less triangular in form, and the

Fig. 121.— Mylacris anthracophilum Scudd. X 2. Carboniferous, Illinois.

space they occupied would be most readily filled by radiating
veins ; such a condition of things, which we find in the
Mylacridce, would naturally precede one in which the mediastinal
vein, to strengthen the part of the wing most liable to strain,
should, as in the Blattinarice, follow the basal curve of the
costal margin, and throw its branches off at intervals toward
the border, much after the fashion of the mediastinal vein.

This view of the relative antiquity of the two tribes of
PalcBoblattaricB is supported by the fact that while in both of
them the internomedian branches show a tendency to repeat
the general course of the anal nervules, as in the corresponding
veins of the costal region, this tendency is lost in modern types ;
and among those ancient Blattinarice, which are esteemed
highest in the series, there is a marked tendenc}^ toward a loss

OF THE PAST. 213

of this repetition of the style of branching of the mediastinal
and anal offshoots by the scapular and internornedian respec-
tively.

A certain amount of geological evidence may also be claimed
in support of this view. A survey of the species of the two
groups found up to the present time in America, published and
unpublished, shows that all the Mylacridce are found below the
Upper Carboniferous, while more than half the Blattinarue are
found in or above it. This results largely from a recent and
as yet unpublished discovery of Blattinarice in the Upper Coal
Measures of Ohio and "West Virginia, which in their general
features are much nearer than previously discovered American
Cockroaches to the European Blattinarice, the latter of which
come generally from Upper Carboniferous beds. The Mylaerida
have therefore been found in America in strata generally
regarded as older than those which in Europe have yielded
Cockroaches, and this gives a sufficient explanation why no
MylacridcB have yet been found in the Old World. In America
one is mostly dealing with absolutely older forms, and they
naturally give that continent a more old-fashioned look, when
we regard the Carboniferous fauna as a whole. As already
stated, a wing from the French Silurian (Pakeobfattma Dounlki
Brongn.) has been claimed as a Cockroach, but without good
reason, and to see a real old Cockroach one must look to
America,

Up to this point we have contrasted the palaeozoic Cockroaches
with the existing forms only, and finding such important dis-
tinctions between them, we naturally turn with some curiosity
to the intermediate mesozoic and tertiary formations.

Now, not only are the mesozoic species as numerous (actually,
but not relatively) as the palaeozoic, but a recent discovery of a
Triassic fauna of considerable extent, in the elevated parks of
Colorado, presents us with a series of intermediate forms
between those peculiar to the Coal Measures and those charac-
teristic of the later mesozoic rocks. Excluding, however, for a
moment this Triassic fauna, we may say of the later mesozoic
species that they are Neoblattarice, not Palceoblattarice, though
they still show some lingering characteristics of their ancestry.
Thus the front wings are in general of a less dense texture than

214

THE COCKROACH

in modern times, but without the perfect diaphaneity of the
palaeozoic species ; in some the anal veins fall in true palceo-
blattarian fashion on the inner margin, while in others which
cannot be dissociated generically from them, the anal veins are
disposed as in modern types. But in all there is a loss of one
of the principal veins, or rather an amalgamation of two or
more — a characteristic of more fundamental character. As a
general rule, moreover, to which wre shall again advert, the
mass of the species are of small size, in very striking contrast
to the older types.

To return now to the Triassic deposits of Colorado, we recog-
nize here an assemblage of forms of a strictly intermediate
character. Here are PalcBoblattarice and Neoblattarice, side by
side. The larger proportion are Palceoblattarice, but all of them
are specifically, and most of them generically, distinct from
palaeozoic species, and all rank high among Blattinarice; still
further, the species are all of moderate size, their general
average being but little above that of mesozoic Cockroaches,

Fig. 122. — NeorthroUattina Lakesii Scudd. X 5. Trias, Colorado.

and only a little more than half that of palaeozoic types. The
Neoblattarice of this Triassic deposit are still smaller, being
actually smaller than the average mesozoic Cockroach, and one
or two of them, of the genus Neortlirollattina (see figure of
N. Lakesii), have marked affinity to one of the genera of
PalceoblattarifB (Poroblattina) peculiar to the same beds, differ-
ing mainly in the union or separation of the mediastinal
and scapular veins ; while others, as Scutmoblattina, have a

OF THE PAST. 215

Phoraspis-like aspect and density of membrane. This novel
assemblage of species bridges over the distinctions between the
Palceoblattarice and Neoblattarice. We find, first, forms in which
the front wings are diaphanous, with distinct mediastinal and
scapular veins, and the anal veinlets run to the border of the
wing (Spitobfattina, Poroblattina) ; next, those having a little
opacity of the front wings, with blended mediastinal and
scapular, and the anal veins as before (some species of Neorthro-
blattina) ; then those with still greater opacity, with the same
structural features (other species of Neorthroblattina) ; next,
those having a coriaceous or leathery structure, blended
mediastinal and scapular, and anal veins falling on the inner
margin (some species of Scutinoblattina) ; and, finally, similarly
thickened wings with blended mediastinal and scapular, and
anal veins impinging on the anal furrow (other species of
Scutinoblattina).

It is not alone, however, by the union of the mediastinal and
scapular stems that the reduction of the veins in the wings of
later Cockroaches has come about ; for in many mesozoic types
the externomediaii vein is blended with one of its neighbours,
while in others not only are the mediastinal and scapular
united, but at the same time the externomedian and interno-
median.

As regards the other structural distinction between the
Pakeoblattarm and Neoblattarice — the course of the anal
nervules — there is much diversity, and very imperfect know-
ledge, since this very portion of the wing is not infrequently
lost, a fracture most readily occurring at the anal furrow. In
most of the mesozoic genera, the anal nervules, as far as known,
strike the margin ; but the larger portion of these show a decided
tendency to trend toward the tip of the anal furrow, as in many
modern forms. This feature can hardly be considered as firmly
established in mesozoic times, and the same genus, as Scutino-
blattina, may contain species which differ in this respect.

A further peculiarity of mesozoic Cockroaches, already
alluded to, is their generally small size. The average length of
the front wing of palaeozoic Cockroaches has been estimated to
be 26 mm., that of the Triassic Palceoblattarice is about 16 mm.,
while that of the mesozoic Neoblattarice is 12 '5 mm. One

216

THE COCKROACH

exception to this small size must be noted in the species from
the Jura of Solenhofen, all of which were large and some
gigantic, one wing reaching the length of 60 mm., or about the
size of our largest tropical Blaberce. If we omit these excep-
tional forms, the average length of the wing of the mesozoic
Cockroach would be scarcely more than 11 mm. Now an
average of the 243 species of which the measurements are
given in Brunner's Systeme des Blattaires (1865), gives the
length of the front wing of living Cockroaches as a little over
18 mm.; so that the mesozoic Cockroaches were as a rule con-
siderably smaller, the palaeozoic Cockroaches much larger, than
the living.

Nearly eighty species of mesozoic Neoblattance are known,
and they are divided into thirteen genera,* one of which,
Mesoblattina (see figure of M. Erodiei), contains upwards of
twenty species, mainly from the Lias and Oolites of England.
The Upper Oolite has proved the most prolific, considerably

Fig. 123. — MesoNattina Brodiei Scudd. X 4. Purbecks, England.

more than half the species having been found in the English
Purbecks, while nearly a fourth occur in the Lias of England,
Switzerland, and Germany. Many of the English species have
been figured in Brodie's Fossil Insects of the Secondary Rocks
of England, in Westwood's paper on Fossil Insects in the
tenth volume of the Quarterly Journal of the Geological
Society, and in the memoir alluded to above. No species has
yet been found in rocks of different geological horizons, and the

* See a paper on mesozoic Cockroaches now printing in the Memoirs Bost. Soc.
Nat. Hist., Vol. III., p. 439 seq.

OF THE PAST.

217

genera of the Trias are peculiar to it. So, too, are some of the
genera of the Oolite, but all of the Liassic genera occur also in
the Oolite.

Among these mesozoic Cockroaches are some of very peculiar
aspect; one, Blattidium (see figure of B. Simyrus), found only
in the lower Purbecks, has ribbon-shaped wings with parallel

Fig. 124. — Blattidium Ximyrus Westw. X 3. Lower Purbecks, England.

sides, longitudinal neuration, and anal nervures with a course
at right angles to their usual direction ; another, Pterinoblattina
(see figure of P. intennixta), geologically widespread, is very
broad, more or less triangular, and has an exceedingly fine and
delicate neuration, so arranged as to resemble the barbs of a
feather.

A comparison of the neuration of the tegmina of mesozoic
and recent Cockroaches, to determine as far as possible the
immediate relations . of the former to existing types, gives
as yet little satisfaction. The prolific genera, Mesoblattina and
Rithma, may be said to bear considerable resemblance to the
PhyttodromidcBj and the peculiar neuration of Elisama is in part
repeated in the Panchloridce, as well as in some PhyUodromidce

218

THE COCKROACH

and EpilampridcB. Scutinollattina also reminds one in certain
features of some Epilampridce, like Phoraspis. The other
genera appear to have no special relations to any existing
type. As a whole, it would appear as if the Blattaricc spinoste
approached closer to the mesozoic forms than do the Blattance
muticce.

Fig. 125. — Pterinoblattina intermixta £cudd. X 4. Upper Lias, England.

As to the tertiary Cockroaches we know very little, exceed-
ingly few having been preserved, even in amber — that
wonderful treasury of fossil Insects. Here first we come
across apterous forms, Polyzosteria having been recognised
in Prussian amber,* together with winged species, which
seem to be Phyllodromidce ; these are the only Blattarice spinosce
known from the Tertiaries. Of the other group, we have
Zetobora, one of the Panchloridce, and Paralatmdia, one of the
Corydidce, from American rocks, and Heterogamia and Homceo-
gamia, one from Parschlug in Steiermark, the other from
Florissant in Colorado, belonging to the sub-family Heteroga-
midce. Others are mentioned, generally under the wide generic
term Elatta, from Oeningen, Eisleben, Rott, and even from
Spitzbergen and Greenland ; but little more than their names
are known to us. Paralatindia, from the Green River beds of
Wyoming, U.S., is the only tertiary Cockroach yet referred
to an extinct genus ; but close attention has not yet been paid
even to the few tertiary Cockroaches which we know. There
is no reason to suppose that they will be found to differ more
from the existing types than is generally the case with other

* The wingless creature from the Carboniferous deposits of Saarbriicken, described
by Goldenberg as a Cockroach, under the name of Polyzostcrites yranosus, appears
to be a Crustacean.

OF THE PAST. 219

Insects. TJie more we learn of caenozoic Insects, the more truly
do we find that the early Tertiary period was in truth the dawn
of the present, the distinction between the faunas of these
remotely separated times (though not to be compared in
character) being scarcely greater than is found to-day between
the Insects of the temperate and torrid zones.

We began this review with the statement that no Insect was
so important palaeontologically as the Cockroach. This would
more clearly appear had we space to pass in review the geologi-
cal history of all the Insect tribes; for then it could be shown
that it was only in the passage from palaeozoic to mesozoic times
that the great ordinal groups of Insects were differentiated, and
that the Triassic period therefore becomes the expectant ground
of the student of fossil Insects. Up to the present time we do
not know half a dozen Insects besides Cockroaches from these
rocks. Yet, notwithstanding this advantage on the part of the
Cockroaches, how meagre is the history, how striking the
"imperfection of the geological record" concerning them, the
following tabulation of the fossil species by their genera will show.

It here appears that there are about 80 species known
from the palaeozoic rocks, two or three more than that from the
mesozoic, and only nine from the csenozoic ! When we call to
mind that half the palaeozoic Insects were Cockroaches, and that
seven or eight hundred species exist to-day, what shall we say
of the paltry dozen* from the rich tertiaries ? Shall we claim
that these figures represent their true numerical proportion to
their numbers in the more distant past? Then, indeed, must
the palaeozoic period have been the Age of Cockroaches ; for all
research into the past shows that a type once losing ground
continues to lose it, and does not again regain its strength.
The Cockroaches of to-day are no longer, as once, a dominant
group ; they are but a fragment of the world's Insect-hosts ;
yet even now the species are numbered by hundreds. If this
be a waning type, what must its numbers have been in the far-
off time, when the warm moisture which they still love was the
prevailing climatic feature of the world ; and how few of that
vast horde have been preserved to us ! The housekeeper will
thank God and take courage.

• This includes all possible forms ; our table shows but nine.

GEOLOGICAL DISTRIBUTION OF FOSSIL

COCKROACHES.

Figures in Italics represent the number of American species ; in roman, of European.

Carboniferous.

Permian.

i-s

Oligocene.

Miocene.

TOTALS.

Lower.

Middle.

PALJEOBLATTABI^E.

Mylacrid(

^ — Mvlacris

Promvlacris

«/

Paromylacris

. .

Lithomylacris . .

Necymylacris

Blattinaricn — Etoblattina

15 + 6

'3 + 1

9 B

. ,

. .

Spiloblattina . .

. .

• *

. .

Archimvlacris .

Anthracoblattina

• *

Gerablattiiia

Hermatoblattina

• *

Progonoblattina

. .

Oryctoblattina . .

. .

Petrablattiiia . .

. .

^ w

B w

. .

. ,

Poroblattina

. .

^ w

* •

, ,

^ m

• *

(23)

(6)

(41)

(11)

(10)

(91)

NEOBLATTARI.I:.

'Ctenoblattina . .

* •

. .

* •

^ %

^ ,

* •

Neorthroblattina . .

. .

. ,

. .

, .

• *

, .

. .

Rithma

w ^

B ^

• *

, %

, .

Mesoblattina

. ,

• *

, ,

. .

<D X
••L CD

Elisama

— — •
Xt """!
d> "

Pterinoblattina

*P 2 <,

Blattidium

* •

% %

• •

^ B

B ^

^ Cw

Nannoblattina

• *

O ^

Dipluroblattina

, -

* •

, .

9 ^

. .

-4J 03

Diechoblattina

. .

, ,

. .

Scutinoblattina

• •

B ^

. .

* •

. .

Legnophora

. %

. .

B a

• *

. .

^ Aporoblattina

. .

. ,

• .

. .

(8)

(17)

(52)

(77)

Phyllodromid<t> — ' ' Blatta " . .

• •

. .

* •

. .

Periplanetidce — Polyzosteria . .

• *

. •

. .

* •

. .

Panchloridce. — Zetobora . .

B ^

, ,

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Corydidca — Paralatindia . .

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B t

t ^

B %

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Heterogamidce — Homteogamia

. .

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Heterogamia

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(8)

(1)

(9)

GRAND TOTALS . .

17 52

177

SAMUEL H. SCUDDER.

APPENDIX

PARASITES OF THE COCKROACH.

Spirillum, sp. [Vibrio]. SCHIZOMYCETES.

Rectum.
Ref.— Biitschli, Zeits. f. wiss. ZooL, Bd. XXL, p. 254 (1871).

Hygrocrocis intestinalis, Val. CYAXOPIIYCE^E.

Filaments of a very minute Alga abound in the rectum of the
Cockroach, where this species is said by Valentin to occur. The
intestine of the Crayfish is given as another habitat. Leidy
observes that the filaments which he found in the rectum of the
Cockroach are inarticulate, and do not agree with Valentin's
description of the species.

7?<?/.— Valentin, Report, f. Anat. u. Phys., Bd. I., p. 110 (1836) ;
Robin, Veget. qui croissent sur 1'Homme, p. 82 (1847) ; Leidy,
Smithsonian Contr., Vol. V., p. 41 (1853) ; Biitschli, Zeits. f. wiss.
ZooL, Bd. XXL, p. 254 (1871).

Endamcdba (Amoeba} JJlattcr, Biitschli. RHIZOPODA.

Rectum.

Ref. — Siebold, Katurg. wirbelloser Thiere (1839) Jide Stein ;
Stein, Organismus d. Infusions-thiere, Bd. II., p. 345 (1867) ;
Biitschli, Zeits. f. wiss. ZooL, Bd. XXX., p. 273, pi. xv. (1878) ;
Leidy, Proc. Acad. N. S. Phil., Oct. 7th, 1879, and Freshwater
Rhizopods of N. America, p. 300 (1879).

Gregarina (Clepsidrina) Jjlattarum, Sieb. GREGARIXIDA.

Encysted in chylific stomach and gizzard ; free in large
intestine.

7?e/.— Siebold, Naturg. wirbelloser Thiere, pp. 56, 71 (1839) ;
Stein, Mull. Arch., 1848, p. 182, pi. ix., figs. 38, 39; Leidy,
Trans. Anier. Phil. Soc., Vol. X., p. 239 (1852) ; Biitchsli, Zeits.
f. wiss. ZooL, Bd. XXL, p. 254 (1871), and Bd. XXXV., p. 384
(1881) ; Schneider, Gregarines des Invertebres, p. 92, pi. xvii.,
figs. 11, 12 (1876).

222 APPENDIX.

Nyctotherus ovalis, Leidy. INFUSORIA.

Small and large intestines.

Ref. — Leidy, TVans. Amer. Phil. Soc., Vol. X., p. 244, pi. xi.
(1352).

Playiotoma (Bursaria) blatta/rum, Stein-. INFUSORIA.

Rectum.
Ref. — Stein, Sitzb. d. -kdnigl. Bohm. Ges., 1860, pp. 49, 50.

Lophomonas JBlattarum, Stein. INFUSORIA.

Rectum.

Ref. — Stein (loc. cit.} ; Biitschli, Zeits. f. wiss. Zool., Bd. XXX.,
p. 258, plates xiii., xv. (1878).

L. striata, Biitschli. INFUSORIA.

Rectum.

.Be/1.— Biitschli, Zeits. f. wiss. Zool., Bd. XXX., p. 261, plates

••• /I D T O\

xm., xv. (187o).

Gordius, sp. NEMATELMINTHA.

Specimens in the Museum at Hamburg, from Venezuela.
Obtained from some species of Cockroach.

Oxyuris Diesingi, Ham. NEMATELMINTHA.

Rectum, frequent.

Ref. — Hammerschmidt, Isis, 1838] Biitschli, Zeits. f. wiss. Zool.,
Bd. XXI., p. 252, pi. xxi. (1871).

0. Blattce orientalis, Ham. NEMATELMINTHA.

Rectum (much rarer than 0. Diesingi).

Ref. — Hammerschmidt (loc. cit.} ; Biitschli, Zeits. f. wiss. Zool.,
Bd. XXL, p. 252, pi. xxiL (1871).

Other species of Oxyuris are said to occur in the same situation,
e.g., 0. gracilis and 0. appendiculata (Leidy, Proc. Acad. N. S.
Phil., Oct. 7th, 1879), and O.macroura (Radkewisch, quoted by
Van Beiieden in Animal Parasites, Engl. trans., p. 248).

Filaria rhytiplewrites, NEMATELMINTHA.

Encysted in the fat-body of the Cockroach ; sexual state in the
alimentary canal of the Rat. Spiroptera, obtusa is similarly
shared by the Meal-worm (larva of Tenebrio molitor) and the
Mouse.

J?e/;_Galeb, Compt. Rend., July 8th, 1878.

APPENDIX. 223

Acarus, sp. ARACHNIDA.

Found by Cornelius upon the sexual organs of a male
• Cockroach.

fief. — Cornelius, Beitr. zur iiahern Kenntniss von Periplaneta
orientalis, p. 35, fig. 23 (1853).

Evania apjjendigaster, L. IXSECTA (Hymenoptera).

A genus of Ichneumons, parasitic upon Periplaneta and Blatta.
T^/.— -Westwood, Trans. Ent. Soc., Vol. III., p. 237 ; Ib., Ser.
II., Vol. L, p. 213.

JSymbius JBlattarum, Sund. INSECTA (Coleoptera).

The apterous female is parasitic upon P. ainericana and B.
yermanica.

Ref. — Sundevall, Isis, 1831.

SENSE OF SMELL IN INSECTS.

SINCE the printing of the sheets which describe the organs of
special sense, we have become acquainted with two experimental
researches of recent date, instituted for the purpose of determining
whether other organs, besides the antennae, may be specially con-
cerned with the perception of odours by Insects.

Prof. Graber (Biol. Centralblatt, Bd. V., 1885) has described
extensive and elaborate experiments upon various Insects, tending
to the conclusion that the palps and the cerci may be sensitive to
odours, and that in special cases the palps may be even more
sensitive in this respect than the antennas. Cockroaches, decapi-
tated, but kept alive for some days, were found to perceive odours
by means of their cerci. His general conclusion is that Insects
have 110 special sense of smell, but that various parts of the surface
of the body are furnished with nerve-endings capable of perceiving
strong odours. Prof. Graber's results are known to us only through
the abstract given by Prof. Plateau in the paper next to be
mentioned.

Prof. Plateau (Compt. rend, de la Soc. Entom. de Belgique, 1886)
relates experiments upon the powers of scent resident in different
organs of the Cockroach. Two Cockroaches had their palps (max-
illary and labial) removed ; two others had the antennae removed.
An evaporating dish, 8 inches in diameter, was then partly filled with

224 APPENDIX.

fine sand. In the centre of the dish was set a circular box of card,
without bottom, 2 inches in diameter, and 14 inches high. In this box
bread moistened with beer, a bait very attractive to Cockroaches,
was placed, and renewed daily. The four Cockroaches were allowed
to run about in the dish outside the box, and to feed upon the
bread at pleasure by climbing over the enclosure. Observations
were made late at night for a month, when it was found that,
except on the first night, when the Insects ran all over the dish,
none of the Cockroaches without antennae made their way to the
food ; while twenty-three times one of the Cockroaches without palps,
but with antennae intact, was found to be feeding ; in one instance,
both were so found.

Plateau observes that a special sense of smell can only be claimed
for organs which are able to detect faint and distant odours, and
that experiments made with powerful odours close to the body of
the Insect may lead to fallacious results. The perception of faint
odours cannot be effected by the palps or cerci of the Cockroach,
but only by the aiitennse.

THE END.

FEINTED BY McCOKQUODALE & CO, LIMITED, LEEDS.

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