is open to very serious objections, to which we can only briefly allude.
The Order Hemiptera with its extensive divisions, Heteroptera, Homoptera,
Coccidae, and Anoplura exhibiting great differences in structure and
considerable divergence in metamorphosis, is treated as only equivalent to
the little group Panorpatae (scorpion-flies); these latter being considered
a distinct order, although they are not very different in structure or
metamorphosis from the Orders he calls Neuroptera and Trichoptera. The
arrangement appears to be specially designed with the view of making the
Orders adopted in it fall into the two groups Ametabola and Metabola. The
propriety of such a course is more than doubtful since very few of the
Ametabola are really without metamorphosis, in the wide sense of that term,
while the Metabola include Insects with various kinds of metamorphosis.
Indeed if we substitute for the term Ametabola the more correct expression,
"Insects with little metamorphosis," and for Metabola the definition,
"Insects with more metamorphosis but of various kinds," we then recognise
that the arrangement {175}is, like all others, a quite artificial one,
while it is of little value, owing to the development of so few Insects
being hitherto fully ascertained.
BRAUER'S CLASSIFICATION.
Professor Brauer has recently proposed[110] to adopt 17 Orders or chief
groups of Insects, arranging them as follows:—
I. APTERYGOGENEA (with one order).
1. _Synaptera_ (= _Aptera_ of our system).
II. PTERYGOGENEA (= all the other Insects of our arrangement).
2. _Dermaptera_ (= _Orthoptera_, Fam. _Forficulidae_ in our
arrangement).
3. _Ephemeridae_ (= a division of _Neuroptera_ in our arrangement).
4. _Odonata_ (= a division of _Neuroptera_ in our arrangement).
5. _Plecoptera_ (= _Neuroptera_, Fam. _Perlidae_ in our
arrangement).
6. _Orthoptera_ (= our _Orthoptera_ - _Forficulidae_ and +
_Embiidae_).
7. _Corrodentia_ (= the families _Termitidae_, _Psocidae_, and
_Mallophaga_, of our _Neuroptera_).
8. _Thysanoptera_ (as with us).
9. _Rhynchota_ (= _Hemiptera_ with us).
10. _Neuroptera_ (= the families _Hemerobiidæ_ and _Sialidæ_ of our
_Neuroptera_).
11. _Panorpatae_ (= the family _Panorpidae_ of our _Neuroptera_).
12. _Trichoptera_ (= the division _Trichoptera_ of _Neuroptera_).
13. _Lepidoptera_ (= as with us).
14. _Diptera_ (= our _Diptera_ - _Aphaniptera_).
15. _Siphonaptera_ (= _Aphaniptera_, a division of _Diptera_ with
us).
16. _Coleoptera_ (= _Coleoptera_).
17. _Hymenoptera_ (as with us).
The chief characters on which Brauer bases his system are: (1) The
existence or absence of wings. (2) The condition of the mouth, and whether
it undergoes radical changes in the ontogeny, arriving thus at the
categories Menognatha, Metagnatha, and Menorhyncha, as we have mentioned on
p. 161. (3) The metamorphosis; the grouping adopted being Ametabola,
Hemimetabola, Metabola. (4) The number of the Malpighian tubules;
Oligonephria, Polynephria. (5) The nature of the wings, the relative
proportions of the thoracic segments, and some other characters.
Brauer's treatise is accompanied by a valuable and in many respects very
sagacious consideration of the generalised characters of the Insecta; as a
classification based partly on generalisations and partly on structures, it
is, so far as the present {176}condition of our knowledge goes, a good one.
But it is of little value as a practical guide, and as a basis for
theoretical speculation it cannot be treated as of importance, because the
generalisations it makes use of are premature, owing to the small
proportion of the forms that have been examined. And even now the groups
adopted are known to be subject to many exceptions.
Thus it begins by a division of Insecta into winged and wingless; but the
winged division is made to comprehend an enormous number of wingless
Insects, whole subdivisions of Orders such as the Mallophaga being placed
in the winged series, although all are without wings. This first division
is indeed entirely theoretical; and if a classification on generalisations
were adopted, it would be more natural to begin with the old division into
Homomorpha and Heteromorpha, and treat the Order Aptera as the first
division of the Homomorpha, while the Heteromorpha would commence with the
Ephemeridae and Odonata, in which, though the individual in the early part
of the ontogeny is very different from the perfect Insect, there is no
marked division of the later larval and the pupal stages. Brauer's system
is also defective inasmuch as it takes no account of the embryological or
oogenetic processes, though these are of equal importance with the later
phases of the Ontogeny. Even as regards the division into Orders, it is far
from being free from reproach; for instance, the separation of the
Dermaptera from the Orthoptera, while Rhynchota remains intact, although
including a more extensive series of heterogeneous forms; the division of
the Neuroptera into widely separated groups, each of which is treated as
equivalent to the great Orders, such as Coleoptera (in which Strepsiptera
are included), Hymenoptera, and Diptera, is not reasonable. The association
of Mallophaga and Termitidae, while Dermaptera are separated from
Orthoptera, is also undeniably arbitrary, and other similar disparities are
to be seen on scrutinising the details of the system.
On comparing the three arrangements we have outlined, it will be seen that
the chief discrepancies they present come under two heads: (1) The
treatment of the Neuroptera, opinions differing as to whether these Insects
shall be grouped as a single Order, or shall be divided into numerous
Orders; and as to what, if this latter course be adopted, the divisions
shall be. (2) The treatment of the parasitic groups Mallophaga,
Aphaniptera, etc. {177}It must be admitted that whichever of the three
systems we have sketched be adopted, the result is, as regards both these
points, open to criticism. The Order Neuroptera, if we take it in the broad
sense, differs from the other Orders in the greater variety of
metamorphosis exhibited by its members; while if, on the contrary, it be
dismembered, we get a number of groups of very unequal extent and not
distinguished from one another by the same decisive and important
characters as are the other Orders of which they are considered equivalent.
The discrepancy exists in nature, and can scarcely be evaded by any system.
A similar observation may be made as to the parasitic groups, viz.
Mallophaga, Anoplura, Aphaniptera, and Strepsiptera. If these be treated as
separate Orders the result is not satisfactory; while, if they be
associated with the larger groups to which they are respectively nearest
allied, it is almost equally unsatisfactory.
We may mention that Packard and Brauer have in their treatises discussed
the question of super-orders, and have gone so far as to propose names for
them. These two authorities do not however agree in their conclusions; and
as the names proposed are of little practical value, and are but rarely met
with, we need not explain them or discuss the comparative merits of the two
systems.
The divisions of inferior value to the Order are, after repeated scrutiny
by many naturalists, becoming of a more satisfactory character, and
notwithstanding various anomalies, may be, many of them, considered fairly
natural.[111] Unfortunately entomologists have not been able to agree on a
system of terminology, so that for these subdivisions terms such as
sub-order, series, legion, section, tribe, etc., are used by different
authorities in ways so various as to cause much confusion. In the following
pages the terms sub-order and series will be used in a somewhat vague
manner, the term sub-order being preferred where the group appears to be an
important one and of a fairly natural character, while the word series will
be adopted when the groups are connected in a conventional manner. The
designation "family" will be used for groups of subordinate importance; and
as regards this term we may remark that systematic entomologists are making
genuine efforts to define the "families" in an accurate and comprehensible
manner. The endeavour to make these systematic {178}families dependent
throughout the Class Insecta on characters of similar morphological value
has, however, scarcely been entered on, and it is perhaps not desirable,
seeing how very small a portion of the Insects of the world have been
critically examined, that much effort should be yet expended on an attempt
of the kind. It must be admitted that the species of Insects should be
obtained before they can be satisfactorily classified, and it is
estimated[112] that at least nine-tenths of the Insects of the world are
still unknown to entomologists.
GEOLOGICAL RECORD.—Although Insects have a very long pedigree, it is as yet
a very imperfect one. The remains of creatures that can be referred to the
Class Insecta have been found, it is said, in Silurian strata; only one or
two of these very early forms are at present known, and the information
about them is by no means satisfactory; if Insects at all—as to which some
doubt exists—they apparently belong to very different forms, though, like
all the earliest fossil Insects, they are winged. In the strata of the
Carboniferous epoch numerous Insects have been detected, in both Europe and
North America. These earlier Insects are by Scudder called
Palaeodictyoptera, and separated from the Insects around us on the ground
that he considers there existed amongst these palaeozoic Insects no ordinal
distinctions such as obtain in the existing forms, but that the primeval
creatures formed a single group of generalised Hexapods. Brauer does not
accept this view, considering that the earlier Insects can be referred to
families existing at the present time and forming parts of the Orthoptera,
Neuroptera, and Hemiptera. The discrepancy between these two authorities
depends to a great extent on the different classifications of existing
Insects that they start from; Scudder treating the wings as of primary
importance, while Brauer assigns to them only a subordinate value. From the
point of view taken in the present work Scudder's view appears to be in the
main correct, though his expression as to the primary fossil Insects
forming a single homogeneous group is erroneous. The Neuroptera, still in
existence, certainly form a heterogeneous group, and it is clear that the
Palaeozoic fossils represent a more diverse assemblage than the present
Neuroptera do.[113]
{179}In the more recent rocks Insect remains become comparatively numerous,
and in Mesozoic strata forms that can satisfactorily be referred to
existing Orders are found, the Palaeodictyoptera of Goldenberg and Scudder
having mostly disappeared; the Blattidae or cockroaches do not apparently
present any great discontinuity between their Palaeozoic and Mesozoic
forms. The Tertiary rocks afford us fairly satisfactory evidence to the
effect that Insects were then more numerous in species than they are at the
present day. At Florissant in Colorado the bed of an ancient lake has been
discovered, and vast quantities of Insect remains have been found in it,
the geographical conditions indicating that the creatures were not brought
from a distance, but were the natural fauna of the locality; and if so we
can only conclude that Insects must have been then more abundant in species
than they are now.
Scudder has informed us[114] that not only were Insects abundant in the
Tertiaries, but that their remains indicate conditions of existence very
similar to what we find around us. "Certain peculiarities of secondary
sexual dimorphism accompanying special forms of communistic life, such as
the neuters and workers in Hymenoptera and the soldiers among the
Termitina, are also found, as would be expected, among the fossils, at
least through the whole series of the Tertiaries. The same may be said of
other sexual characteristics, such as the stridulating organs of the
Orthoptera, and of peculiarities of oviposition, as seen in the huge
egg-capsules of an extinct Sialid of the early Tertiaries. The viviparity
of the ancient Aphides is suggested, according to Buckton, by the
appearance of one of the specimens from the Oligocene of Florissant, while
some of the more extraordinary forms of parasitism are indicated at a time
equally remote by the occurrence in amber of the triungulin larva of
_Meloe_, already alluded to, and of a characteristic strepsipterous Insect;
not only, too, are the present tribes of gall-making Insects abundant in
the Tertiaries, but their galls as well have been found."
{180}CHAPTER VII
THE ORDER APTERA–DEFINITION–CHIEF CHARACTERISTICS–THYSANURA–CAMPODEA–
JAPYX–MACHILIS–LEPISMA–DIVERSITY OF INTERNAL STRUCTURE IN THYSANURA–
ECTOTROPHI AND ENTOTROPHI–COLLEMBOLA–LIPURIDAE–PODURIDAE–SMYNTHURIDAE–
THE SPRING–THE VENTRAL TUBE–ABDOMINAL APPENDAGES–PROSTEMMATIC ORGAN–
TRACHEAL SYSTEM–ANURIDA MARITIMA–COLLEMBOLA ON SNOW–LIFE-HISTORIES OF
COLLEMBOLA–FOSSIL APTERA–APTERYGOGENEA–ANTIQUITY AND DISTRIBUTION OF
CAMPODEA.
ORDER I. APTERA.
_Small Insects with weak outer skin, destitute throughout life of wings
or their rudiments, but with three pairs of legs; antennae large or
moderate in size._
The above definition is the only one that can at present be framed to apply
to all the Insects included in our Aptera. Unfortunately it is far from
diagnostic, for it does not enable us to distinguish the Aptera from the
larvae or young individuals of many Insects of other Orders. There are,
however, certain characters existing in many species of Aptera that enable
their possessors to be recognised with ease, though, as they are quite
wanting in other members, they cannot correctly be included in a definition
applying to the whole of the Order.
We are thus brought in view of two of the most important generalisations
connected with the Aptera, viz. that these Insects in their external form
remain throughout their life in a condition resembling the larval state of
other Insects, and that they nevertheless exhibit extreme variety in
structural characters.
The more important of the special characters alluded to above {181}as being
possessed by some but not by all members of the Order are (1) a remarkable
leaping apparatus, consisting of two elongate processes at the under side
of the termination of the body; (2) a peculiar ventral tube, usually seen
in the condition of a papilla with invaginated summit, and placed on the
first abdominal segment (see Fig. 100, p. 194); (3) the scales covering the
body; (4) the existence of abdominal appendages in the form of long cerci
or processes at the termination of the body, or of short processes on the
sides of the under surface of the abdominal segments.
Throughout the Order the general shape approximates to that of a larva;
this is shown by the diagrammatic section of the body of _Machilis_ (Fig.
90). There is a succession of rings differing little from one another,
except so far as the head is concerned; even the division of thorax from
abdomen is but little evident, and although in some of the forms the three
thoracic segments may differ considerably among themselves, yet they never
assume the consolidated form that they do to a greater or less extent in
the imago stage of the other Orders. Fig. 90 shows the larva-like structure
of the body, and also exhibits the inequalities in size between some of the
dorsal and the corresponding ventral plates. This phenomenon is here
displayed only to a small extent, so that the true relations of the dorsal
and ventral plates can be readily detected; but in the higher Insects want
of correspondence of this kind may be much more extensive.
[Illustration: FIG. 90.--Section of body of _Machilis_: _o_, ovipositor.
(After Oudemans.)]
The respiratory system is in many of these Insects very inferior in
development, and may even be, so far as tracheae and spiracles are
concerned, entirely absent, but in other members of the Aptera it is well
developed. In the other internal organs there is also great variety, as
there is in the external structure.
A brief explanation as to the term Aptera, which we have adopted as the
name of this Order, is necessary. This name was used by Linnaeus for our
Insects, but as he associated with them various other heterogeneous forms
which were afterwards separated, his "Aptera" became completely broken up
and ceased {182}to be recognised as an Order of Insects. The term was,
however, revived by Haeckel and Balfour several years since, and applied
quite properly to the Insects we have in view. Subsequently Packard and
Brauer, recognising the claims of these Insects to an isolated position,
proposed for them the names Synaptera and Apterygogenea, and Packard has
also used the term Cinura. There is, however, clearly an advantage in
retaining the termination "ptera" for each of the Orders of Insects; and as
the fact that "Aptera" of Linnaeus included many Insects is not a
sufficient reason for refusing to apply the term to a portion of the forms
he used it for, we may, it is clear, make use of the Linnaean name with
propriety, it being explicitly stated that the Order does not include by
any means all the apterous forms of Insects.
The Order includes two sub-orders, viz. (1) _Thysanura_, in which the hind
body (abdomen) is composed of ten segments, and there is no ventral tube on
its first segment; and (2) _Collembola_, in which the hind body consists of
not more than six segments, the first of which is furnished beneath with a
peculiar tube or papilla.
THYSANURA.
Our knowledge of this important sub-order has been recently much increased
by the works of Grassi[115] and Oudemans.[116] Very little is known,
however, of the extra-European forms, there being great difficulties in the
way of collecting and preserving specimens of these Insects in such a way
as to render them available for study and accurate comparison. Grassi and
Rovelli[117] recognise four families among the few European species of
Thysanura, viz. Campodeidae, Japygidae, Machilidae, Lepismidae. Campodeidae
is perhaps limited to a single species, only one having been satisfactorily
established, though several descriptions have been made of what are
supposed to be other species.
This Insect (_Campodea staphylinus_) is, so far as external form goes, well
known, from its having been figured in many works on natural history on
account of its having been supposed to be {183}the nearest living
representative of a primitive or ancestral Insect. The creature itself is
but little known even to entomologists, although it is one of the commonest
of Insects over a large part of Europe. It is numerous in the gardens and
fields about London and Cambridge, and abounds in damp decaying wood in the
New Forest; if there be only one species, it must possess an extraordinary
capacity for adapting itself to extremes of climate, as we have found it at
midsummer near the shores of the Mediterranean in company with the
subtropical white ants, and within a day or two of the same time noticed it
to be abundant on the actual summit of Mount Canigou, one of the higher
Pyrenees, where the conditions were almost arctic, and it was nearly the
only Insect to be found. The species is said to exist also in North America
and in East India. It is a fragile, soft Insect of white colour, bending
itself freely to either side like a Myriapod; the legs are rather long, the
antennae are long and delicate, and the two processes, or cerci, at the
other extremity of the body are remarkably similar to antennae. It has no
eyes and shuns the light, disappearing very quickly in the earth after it
has been exposed. If placed in a glass tube it usually dies speedily, and
is so extremely delicate that it is difficult to pick it up even with a
camel's hair brush without breaking it; so that we may fear it to be almost
hopeless to get enough specimens from different parts of the world to learn
what differences may exist amongst the individuals of this so-called
primitive Insect. Meinert, a very able entomologist, considers that there
is really more than one species of _Campodea_.
[Illustration: FIG. 91.—_Campodea staphylinus._ (After Lubbock, × 15.)]
Campodeidae as a family may be briefly defined as Thysanura with the trophi
buried in the head and with the body terminated by antenna-like processes.
We shall consider some of the anatomical peculiarities of this interesting
Insect after we have {184}briefly reviewed some of the external characters
of the other Thysanura.
The second family (Japygidae) consists of one genus _Japyx_, of which there
are, no doubt, several different species in various parts of the world,
such having already been detected in tropical Africa, in Malasia, and in
Mexico, as well as in Madeira and Europe. The commoner species of the
latter continent, _Japyx solifugus_, lives in moss or in shady places on
the edges of woods. It possesses a great resemblance to a newly-hatched
earwig, and the writer has found it in France under a stone in company with
a number of the tiny creatures it was so much like. This species has been
found as far north as Paris, but has not been met with in Britain. The
family Japygidae is, like the Campodeidae, entotrophous, and is
distinguished by the body being terminated behind by a pair of forceps
instead of antennary organs.
The other two families of Thysanura, Machilidae and Lepismidae, are
ectotrophous—that is, the parts of the mouth are not buried in the head,
but are arranged in the fashion usual in mandibulate Insects.
Only one genus of Machilidae is known, but it is no doubt very numerous in
species, and probably is distributed over most of the globe. _Machilis
maritima_ is common in some places on the coast of England. Another species
(_M. polypoda_) occurs amongst dead leaves in the New Forest, and we have
also observed a species of the genus under the loose stones that frequently
form the tops of the "dykes" or piled walls in Scotland. In more southern
Europe species of _Machilis_ are commonly met with on the perpendicular
faces of very large stones or rocks, over which they glide with wonderful
facility. The scales on the bodies of these rock-inhabiting species form
pretty patterns, but are detached with such facility that it is almost
impossible to obtain specimens in satisfactory condition for examination.
In Machilidae the dorsal plates of the hind body are reflexed to the under
surface so as to form an imbrication covering the sides of the ventral
plates, and the eyes are largely developed; by which characters the family
is distinguished from the Lepismidae. The pair of large compound eyes (Fig.
92, _O_) is a remarkable feature, being indeed unique in the Aptera. The
structures (_o_, _o′_) that Oudemans considers to be simple eyes have, in
external appearance, a resemblance to the fenestrae of the {185}Blattidae;
Grassi states, however, that not only are they eyes, but that they are of
almost unique structure, being, in fact, intermediate between simple and
compound eyes.
The mode of development of the compound eyes of _Machilis_ is of
considerable interest, but unfortunately very little is known about it,
even the period at which the eyes appear being uncertain. Judging from
analogy with the Orthoptera, we should suppose them to be present when the
Insect leaves the egg, and Oudemans apparently considers this to be the
case, but Bolivar states[118] that in the early stages of _Machilis_ the
eyes are only simple eyes; these being replaced by compound eyes in the
later life. The writer has observed very young individuals of _Machilis
polypoda_, and found the eyes to be evidently compound.
[Illustration: FIG. 92.—Head of _Machilis maritima_ (after Oudemans): _A_,
base of antenna; _C_, clypeus; _F_, vertex; _P_, fold; _O_, eye; _o_, _o′_,
supposed simple eye; _M_, mandible; _m_, maxilla; _L_, upper lip; _l_,
lower lip; _T_, portion of maxillary palp; _t_, of labial palp. × 20.]
[Illustration: FIG. 93.—_Lepisma cincta._ (After Oudemans.) × 4. (The line
indicates the natural length.)]
The remaining family of Thysanura, the Lepismidae, is in certain respects
the most highly developed of the Order. The covering of scales found on the
body is very remarkable in some of the species, especially in the genus
_Lepisma_ (Fig. 93, _L. cincta_); the thoracic segments are different from
one another {186}and from those of the abdomen, and the tracheal system is
more highly developed than it is in the Machilidae. Several genera are
known, but only two members of the family have yet been detected in
Britain. One of them (_Lepisma saccharina_), occurs only in houses, and is
sometimes called the silver fish; it is, when full grown, less than half an
inch long, and is covered with scales that give it a feebly metallic
lustre. Like the other Thysanura, its movements are very perfect. It is
said that it is occasionally injurious by nibbling paper, but the writer's
observations lead him to doubt this; its usual food is doubtless
farinaceous or saccharine matter. _Thermobia furnorum_, our other British
Lepismid, has only recently been discovered; it is found in bakehouses at
Cambridge and elsewhere. The bakers call these Insects fire-brats,
apparently considering them to be fond of heat.
Much valuable information as to the anatomy of Thysanura has been obtained
by Grassi and Oudemans, and is of great interest. Taking four genera, viz.
_Campodea_, _Japyx_, _Machilis_, and _Lepisma_, to represent the four
families constituting the sub-order, we will briefly enumerate some of the
more remarkable of the characters of their internal anatomy. _Campodea_ has
a very inferior development of the tracheal system; there are three pairs
of spiracles, which are situate on the thoracic region; the tracheae
connected with each spiracle remain distinct, not uniting with those coming
from another spiracle; there are thus six separate small tracheal systems,
three on each side of the body. _Japyx solifugus_ has eleven pairs of
spiracles, of which four are thoracic; the tracheae are united into one
system on each side by means of lateral tubes; thus there are two extensive
tracheal systems situate one on each side of the body, there being a single
transverse tube, placed near the posterior extremity, uniting the two
lateral systems. In _Machilis_ there are nine pairs of stigmata, two of
them thoracic, seven abdominal; the tracheae from each spiracle remain
unconnected, so that there are eighteen separate tracheal systems, some of
which are considerably more developed than others. The Lepismidae have ten
pairs of stigmata, and the tracheae connected with them are completely
united into one system by longitudinal and transverse tubes. Besides these
differences there are others, of considerable importance, in the position
of the stigmata.
{187}All the Thysanura possess salivary glands. In _Campodea_ there are
about sixteen extremely short Malpighian tubules, or perhaps glands
representing these organs; _Japyx_ is destitute of these structures;
_Machilis maritima_ has twenty elongate tubules; in _Lepisma_ also they are
long, and apparently vary in number from four to eight in different
species. The proportions of the three divisions of the alimentary canal
differ extremely; there is a very large proventriculus in _Lepisma_, but
not in the other families; coecal diverticula are present on the anterior
part of the true stomach in _Machilis_ and in _Lepisma_, but are wanting in
_Campodea_ and in _Japyx_.
The dorsal vessel seems not to present any great differences in the
sub-order. Grassi says there are no alary muscles present, but Oudemans
describes them as existing in _Machilis_, but as being excessively
delicate.
The ventral chain of nerve-ganglia consists in _Campodea_ of one cephalic
ganglion, one sub-oesophageal (which clearly belongs to the ventral series
of ganglia), three thoracic, and seven abdominal. In the other families
there are eight instead of seven abdominal ganglia.
The structure of the internal sexual organs is very remarkable in the
Thysanura. In _Campodea_ there is one extremely large, simple tube on each
side of the body. In _Japyx_ there are seven small tubes on each side,
placed one in each of the successive abdominal segments, and opening into a
common duct. In _Machilis_ there are also seven tubes opening into a common
duct, but the arrangement is no longer a distinctly segmental one. In
_Lepisma_ there are five egg-tubes on each side, the arrangement being
segmental in the young state but not in the adult condition. In _Campodea_
nutrient cells alternate with the eggs in the tubes, but this is not the
case in the other families. Fig. 94 shows the ovaries in three of the
Thysanura; in the drawing representing this part in _Machilis_ (C), one of
the two ovaries is cut away for the sake of clearness.
The male organs in _Campodea_ are very similar in size and arrangement to
the ovaries, there being a single large tube or sac and a short vas
deferens on each side of the body. In _Japyx_ there is a sac on each side,
but it is rendered double by a coecum at its base, and there are long and
tortuous vasa deferentia. In _Lepisma_ there are three pairs of coeca on
each {188}side, segmentally placed and opening into a common duct. In
_Machilis_ there are three retort-shaped sacs on each side opening near one
another into a common duct, the vasa deferentia are elongate, and are very
curiously formed, being each double for a considerable length, and the
separated portions connected at intervals by five transverse commissural
ducts.
[Illustration: FIG. 94.—Ovaries of Thysanura: A, of _Campodea_; B, of
_Japyx_; C, of _Machilis_. (After Grassi and Oudemans.)]
One of the characteristic features of Insect structure is the restriction
of articulated legs to the thoracic region. In the Thysanura there exist
appendages occupying a position on the hind body somewhat similar to that
of the legs on the thorax. These appendages are quite small bodies, and are
placed at the hind margins of the ventral plates of the abdomen, one near
each side; they are connected by a simple joint to the sternite and are
provided with muscles. They are found in _Campodea_ on segments 2 to 7; in
_Lepisma_ on 8 and 9, in the allied _Nicoletia_ on 2 to 9; in _Japyx_ on 1
to 7, being, however, more rudimentary than they are in _Campodea_. In
_Machilis_ they attain perhaps their greatest development and exist on
segments 2 to 9; moreover, in this genus such appendages occur also on the
coxae of the second and third pairs of thoracic legs. Oudemans thinks they
help to support the abdomen, and that they also assist in leaping; Grassi
considers that they are supporting agents to some extent, but that they are
essentially tactile organs. He calls them false legs "Pseudozampe."
Still more remarkable and obscure in function are the vesicles found near
the appendages; we figure a pair after Oudemans, showing them in the
exserted state. In the retracted state the outer portion of the vesicles is
withdrawn into the basal part _P_ (Fig. 95), so that the vesicles are then
only just visible, being {189}concealed by the ventral plate. The abdominal
appendage is not retractile. In _Machilis_ there are twenty-two of these
vesicles, arranged either two or four on one ventral plate of the hind
body. They are also present in _Campodea_, where there are six pairs. They
are usually said to be absent in _Japyx_ and in _Lepisma_, but Haase
shows[119] that _Japyx_ possess a pair placed behind the second ventral
plate of the abdomen. The vesicles appear to be exserted by the entrance of
blood into them, and to be retracted by muscular agency. Much difference of
opinion prevails as to their function; it appears probable that they may be
respiratory, as suggested by Oudemans.
The scales found on the bodies of the Ectotrophous Thysanura may be looked
on as modified hairs, and are essentially similar to those of the
Lepidoptera, and they drop off as readily as do those of the Lepidoptera.
Stummer-Traunfels, who has recently published[120] the results of his
researches on the mouth-organs of Thysanura and Collembola, confirms the
division of the Thysanura into Entotrophi and Ectotrophi, and considers
that the Collembola agree with the former group. The German author
therefore proposes to divide our Aptera, not into Thysanura and Collembola,
but into Ectognathi and Entognathi, the former group consisting of
Machilidae and Lepismidae, the latter of Campodeidae, Japygidae and the
various families of Collembola. We think it far more natural, however, to
retain the older division into Thysanura and Collembola.
[Illustration: FIG. 95.—Abdominal appendage and exsertile vesicles of
_Machilis_. _A_, appendage; _V_, vesicles protruded; _P_, basal portion;
_R_, muscles, × 70.]
COLLEMBOLA.
The sub-order Collembola, which we have defined on p. 182, consists of
small Insects, many of which possess the capacity of leaping, or springing
suddenly, and when disturbed or alarmed naturally make use of this means of
escaping. Their leaps, however, appear to be made quite at random, and very
frequently do {190}not have the result of taking the creature into
concealment, and in such circumstances they may be rapidly and frequently
repeated until the Insect feels itself, as we may suppose, in a position of
safety. Three families may be very readily distinguished, viz. (1)
Lipuridae, in which no leaping apparatus is present; (2) Poduridae, a
leaping apparatus exists near the extremity of the abdomen; the body is
subcylindric and evidently segmented; (3) Smynthuridae, a leaping apparatus
exists: the body is sub-globular with comparatively large head and abdomen,
the intervening thoracic region being small; the segmentation of the body
is obscure.
The study of the Collembola is much less advanced than that of the
Thysanura, comparatively little having been added to our knowledge of the
group since Lubbock's monograph of the British forms was published by the
Ray Society in 1873. Why the Collembola should be neglected when the
Thysanura attract so much attention is as inexplicable as many other
fashions are.
The family Lipuridae consists of a few very small and obscure Insects of
soft consistence. They move slowly, and, owing to the absence of any
leaping power, attract attention less readily than the other Collembola do.
Two genera are generally recognised, and they should probably form separate
families; indeed, in Lubbock's arrangement they do so. In one of the genera
(_Anoura_) the mouth is very imperfect, no mandibles or maxillae having
been detected, while in the other genus (_Lipura_) these organs exist.
In the members of the family Poduridae, including the Degeeriidae of
Lubbock, a saltatory apparatus is present in the form of appendages
attached to the fifth abdominal segment (Degeeriides), or to the fourth
(Podurides). These appendages are during life flexed beneath the body, but
in dead specimens usually project backwards, having the appearance of a
bifid tail. Poduridae are of elongate form, somewhat like small
caterpillars, and are frequently prettily marked with variegate colours.
Fig. 97 represents an arctic form closely allied to our native genus
_Isotoma_.
[Illustration: FIG. 96.—_Lipura burmeisteri_. (After Lubbock.)]
{191}The peculiar shape of the members of the Smynthuridae is sufficient
for their identification. They possess a very convex abdomen, and very near
to it a large head, the intervening chink being occupied by the small
thorax. The segmentation of the body is not easily distinguished. Nicolet
states that the thorax consists of three segments and the abdomen of the
same number, and that when the Insect emerges from the egg these divisions
can be perceived. In after life the posterior part of the thorax becomes
amalgamated with the abdomen, so that it is difficult to trace the
divisions, but there appears to be no information as to the manner in which
this change occurs. Some of these minute Insects frequent trees and bushes,
and their leaping powers are very perfect, so that it is difficult to
capture them. The family includes both the Smynthuridae and the Papiriidae
of Lubbock.
[Illustration: FIG. 97.—_Corynothrix borealis_: _a_, ventral tube; _b_, the
spring. (After Tullberg.)]
[Illustration: FIG. 98.—_Smynthurus variegatus_, with spring extended.
(After Tullberg.)]
The two most characteristic organs of the Collembola are the spring and the
ventral tube. The first of these is an elongate structure attached to the
underside of the abdomen near its extremity, either on the penultimate or
ante-penultimate segment. It consists of a basal part, and of two
appendages attached thereto. It is carried under the Insect bent forwards,
and is retained in this position by means of a catch which projects from
the under surface of the third segment of the body, descending between the
two branches of the spring, and passing under the extremity of its basal
segment. It is considered that the spring is elastic, is flexed under the
body by muscular action, and, being retained in this position {192}of
restraint by the catch, when the latter is removed the spring extends by
reason of its elasticity, and the leap is thus executed. Whether this is
really the exact method of leaping is, however, doubtful, for Lubbock says
that the catch "only exists in certain genera"; while in its structure it
does not appear to be well calculated to retain in position an organ that
by virtue of its elasticity is constantly exerting a considerable force.
[Illustration: FIG. 99.—_Smynthurus fuscus_, with exsertile vesicle (_a_)
protruded from ventral tube; _b_, the spring extended.]
The ventral tube is an anomalous and enigmatic structure. In the lower
forms, such as _Lipura_ or _Anurida_, it consists merely of a papilla (Fig.
100, A, _a_) more or less divided by fissure into two parts. In the
Smynthuridae it is more highly developed, and protects two long delicate
tubes that are capable of being protruded, as shown in the outline profile
of _Smynthurus fuscus_ (Fig. 99), which is taken from specimens preserved
in balsam by Mr. J. J. Lister. The nature and use of this ventral tube have
given rise to much discussion. Lubbock considered, and others have agreed
with him, that it serves to attach the Insect to bodies to which it may be
desirable the Insect should, when in the perpendicular position, adhere.
Reuter[121] assigns a quite different function to this singular structure.
He states that the hairs of the body are hygroscopic, and that the peculiar
claws of the Insect having collected the moisture from the hairs, the
ventral tube becomes the means of introducing the liquid into the body.
These Insects possess, however, a mouth, and there seems to be no reason
why a complex apparatus should be required in addition to it for so simple
a purpose as the introduction of moisture to the interior of the body.
Haase finds[122] that Collembola can crawl on glass without the aid of the
ventral tube; he considers its function to be physiological, and that it
may probably be respiratory as it has been suggested is the case with the
vesicles of Thysanura. The function of the ventral tube is certainly not
yet satisfactorily elucidated. The vesicles contained in it are said to be
extruded by blood-pressure, and withdrawn by muscular action in a manner
similar to that which we have described as occurring {193}in the case of
the exsertile vesicles of the Thysanura. The processes in _Smynthurus_ bear
glandular structures at their extremities. It has been suggested that the
ventral tube of Collembola is the homologue of a pair of ventral
appendages. The term Collophore has been applied to it somewhat
prematurely, seeing the doubt that still exists as to its function.
Some of the Collembola possess a very curious structure called the
prostemmatic or ante-ocular organ; its nature and function have been very
inadequately investigated. The ocular organs of the Collembola consist,
when they are present, of isolated ocelli placed at the sides of the head
like the corresponding organs of caterpillars; the prostemmate is placed
slightly in front of the group of ocelli, and has a concentric arrangement
of its parts, reminding one somewhat of the compound eyes of the higher
Insects. This structure is represented in Fig. 100, B, C; it is said by Sir
John Lubbock to be present in some of the Lipuridae that have no ocelli,
and he therefore prefers to speak of it as the "post-antennal" organ.
A very characteristic feature in the Collembola is the slight development
of the tracheal system. Although writers are far from being in accord as to
details, it seems that stigmata and tracheae are usually absent. In
_Smynthurus_ there are, however, according to Lubbock,—whose statement is
confirmed by Meinert and Tullberg,—a pair of stigmata situate on the head
below the antennae, and from these there extends a tracheal system
throughout the body. Such a position for stigmata is almost, if not quite
unique in Insects; Grassi, however, seems to have found something of the
kind existing in the embryo of the bee.
At present only a small number of species of the Order Aptera are known;
Lubbock recognised about sixty British species, and Finot sixty-five as
found in France. The North American forms have not received so much
attention as the European, and the Aptera of other countries, though they
are probably everywhere fairly numerous, are scarcely known at all. A few
have been described from the Indo-Malayan region and some from Chili, and
the writer has seen species from the West Indian and Sandwich Islands. All
the exotic forms as yet detected are very similar to those of Europe.
The Thysanura are probably not very numerous in species, and appear to be
in general intolerant of cold. With the Collembola {194}the reverse is the
case. They are excessively numerous in individuals; they are found nearly
everywhere on the surface of the ground in climatic conditions like those
of our country, while no less than sixteen species have been found in Nova
Zembla and one each in Kerguelen and South Georgia. One species, if not
more, of _Podura_, lives on the surface of stagnant waters, on which the
minute creatures may frequently be seen leaping about in great numbers
after being disturbed.
In 1874 the plain of Gennevilliers in France was copiously irrigated; in
the following year the soil was still very damp, and there existed numerous
pools of stagnant water, on the surface of which _Podura aquatica_ was
developed in such prodigious quantity as to excite the astonishment of the
inhabitants of the region.
Accounts have been frequently given of the occurrence on snow and glaciers
of Insects spoken of as snow-fleas, or snow-worms. These mostly relate to
Poduridae, which are sometimes found in countless number in such
situations. The reason for this is not well understood. According to F.
Löw,[123] on the 17th of March at St. Jacob in Carinthia, Parson Kaiser
observed, on the occurrence of the first thaw-weather, enormous numbers of
a Podura (? _Achorutes murorum_) on the surface of the snow for an extent
of about half a mile, the snow being rendered black in appearance by them;
eleven days afterwards they were found in diminished numbers on the snow,
but in large quantity on the water left by its melting. This account
suggests that the occurrence of the Insects on the snow was merely an
incident during their passage from the land, where they had been
hibernating, to the surface of the water.
One little member of the Lipuridae, _Anurida maritima_ (_Lipura maritima_
of Lubbock), has the habit, very unusual for an Insect, of frequenting salt
water. It lives amongst the rocks on the shores of the English Channel,
between high and low tide-marks. Its habits have been to some extent
observed by Laboulbène[124] and Moniez[125]; it appears to be gregarious,
and when the tide is high, to shelter itself against the commotions of the
water in chinks of the rocks and other positions of advantage. When the
tide is out the Insects apparently delight to {195}congregate in masses on
the surface of the rock pools. This _Anurida_ can endure prolonged
immersion; but both the observers we are quoting say that it is, when
submerged, usually completely covered with a coat of air so that the water
does not touch it. The little creature can, however, it would appear,
subsist for some time in the pools of salt water, even when it is not
surrounded by its customary protecting envelope of the more congenial
element. Its food is said, on very slender evidence, to consist of the
remains of small marine animals, such as Molluscs. We reproduce some of
Laboulbène's figures (Fig. 100); the under-surface shows at a the divided
papilla of the ventral tube; B, C represent the peculiar prostemmatic
organ, alluded to on p. 193, in its mature and immature states.
[Illustration: FIG. 100.—_Anurida maritima_: A, under-surface; _a_, papilla
of ventral tube; B, prostemmatic organ of young; C, of adult. (After
Laboulbène.)]
Very little information exists as to the life-history of the Aptera; as for
their food, it is generally considered to consist of refuse vegetable or
animal matter. It is usual to say that they are completely destitute of
metamorphosis, but Templeton says of _Lepisma niveo-fasciata_ that "the
young differ so much from the mature Insect that I took them at first for a
distinct species; the thoracic plates are proportionately less broad, and
the first is devoid of the white marginal band." As regards the moults, it
would appear that in this, as in so many other points, great diversity
prevails, Grassi stating that in _Campodea_ there is a single fragmentary
casting of the skin; and Sommer informing us that in _Macrotoma plumbea_
the moults are not only numerous, but continue, after the creature has
attained its full growth, throughout life.
A very marked feature of the Aptera is their intolerance of a dry
atmosphere. Although _Campodea_ can exist under very diverse conditions, it
dies very soon after being placed in a dry closed tube; and the same
susceptibility appears to be shared by all the other members of the Order,
though it is not so extreme in all; possibly it may be due to some
peculiarity in the structure {196}of the integument. So far as tolerance of
heat and cold goes, the Aptera can apparently exist in any climate, for
though some of the species extend to the Arctic regions, others are
peculiar to the tropics.
_Thysanura_ are recorded by Klebs and Scudder as occurring commonly in
amber; the latter author has described a fossil, supposed to be a
_Lepisma_, found in the Tertiary deposits at Florissant. Scudder has also
described another fossil, likewise from Florissant, which he considers to
form a special sub-order of Thysanura—_Ballostoma_—but it is extremely
doubtful whether this anomalous creature should be assigned to the Order at
all. A still older fossil, _Dasyleptus lucasii_ Brongniart, from the
Carboniferous strata in France, is considered to belong to the Order
Aptera, but it must be admitted there is some doubt on this point.
The interest aroused in the minds of naturalists by the comparatively
simple forms of these purely wingless and therefore anomalous Insects has
been accompanied by much discussion as to their relations to other Insects,
and as to whether they are really primitive forms, or whether they may
perhaps be degenerate descendants from some less unusual states of
Insect-life. Mayer and Brauer dissociated our Aptera entirely from other
Insects, and proposed to consider the Hexapoda as being composed of two
groups—(1) the Apterygogenea, consisting of the few species we have been
specially considering; and (2) the Pterygogenea, including all the rest of
the immense crowd of Insect forms. They were not, however, able to
accompany their proposed division by any satisfactory characters of
distinction, and the subsequent progress of knowledge has not supported
their view, all the best investigators having found it necessary to
recognise the extremely intimate relations of these Insects with the
Orthoptera. Meinert thought that _Lepisma_ must be included in the
Orthoptera; Grassi proposes to consider the Thysanura as a distinct
division of Orthoptera; and Oudemans recognises the close relations
existing between _Machilis_ and Orthoptera proper. Finot includes the
Aptera in his Orthoptères de la France, and a species of _Japyx_ has
actually been described by a competent entomologist as an apterous earwig.
At present, therefore, we must conclude that no good distinction has been
found to justify the separation of the Aptera from all other Insects.
{197}The taxonomy of the Collembola has not yet been adequately treated,
and it is possible that more grounds will be found for separating them as a
distinct Order from the Thysanura,—a course that was advocated by
Lubbock,—than exist for dividing these latter from the Orthoptera proper.
There are apparently no grounds for considering the Aptera to be degenerate
Insects, and we may adopt the view of Grassi, that they are primitive, or
rather little evolved forms. It must be admitted that there are not at
present any sufficient reasons for considering these Insects to be
"ancient" or "ancestral." The vague general resemblance of _Campodea_ to
many young Insects of very different kinds is clearly the correlative of
its simple form, and is no more proof of actual ancestry to them than their
resemblances _inter se_ are proofs of ancestry to one another. But even if
deprived of its claim to antiquity and to ancestral honours, it must be
admitted that _Campodea_ is an interesting creature. In its structure one
of the most fragile of organisms, with a very feeble respiratory system,
inadequate organs of sense, only one pair of ovarian tubes, very imperfect
mouth-organs, and a simple alimentary canal, it nevertheless flourishes
while highly-endowed Insects become extinct. In the suburban gardens of
London, on the shores of the Mediterranean, on the summits of the higher
Pyrenees, in North America even it is said in the caves of Kentucky, and in
India, _Campodea_ is at home, and will probably always be with us.
{198}CHAPTER VIII
ORTHOPTERA—FORFICULIDAE, EARWIGS—HEMIMERIDAE
ORDER II.—ORTHOPTERA.
_Insects with the mouth parts conspicuous, formed for biting, the four
palpi very distinct, the lower lip longitudinally divided in the middle.
The tegmina (mesothoracic wings), of parchment-like consistence, in
repose closed on the back of the Insect so as to protect it. The
metathoracic wings, of more delicate consistence, ample, furnished with
radiating or divergent nervures starting from the point of articulation,
and with short cross nervules forming a sort of network; in repose
collapsing like a fan, and more or less completely covered by the tegmina
(except in certain Phasmidae, where, though the wings are ample, the
tegmina are minute, so that the wings are uncovered). In a few forms
(winged Forficulidae and some Blattidae) the metathoracic wings are, in
addition to the longitudinal folding, contracted by means of one or two
transverse folds. The mode of growth of each individual is a gradual
increase of size, without any abrupt change of form, except that the
wings are only fully developed in the final condition. There is no
special pupal instar. Species in which the wings are absent or
rudimentary are numerous._
The Orthoptera are Insects of comparatively large size. The Order, indeed,
includes the largest of existing Insects, while none are so minute as many
of the members of the other Orders are; three millimetres is the least
length known for an Orthopterous Insect, and there are very few so small,
though this is ten times the length of the smallest beetle. The Order
includes earwigs, cockroaches, soothsayers or praying-insects, stick- and
leaf-insects, grasshoppers, locusts, green grasshoppers, and crickets.
{199}The changes of form that accompany the growth of the individual are
much less abrupt and conspicuous than they are in most other Insects. The
metamorphosis is therefore called Paurometabolous. It has been supposed by
some naturalists that Orthoptera go through a larger portion of their
development in the egg than other Insects do. This does not clearly appear
to be the case, though it seems that there are distinctions of a general
character in the embryology; the period of development in the egg is
prolonged, and the yolk is said by Wheeler[126] to be more than usually
abundant in comparison with the size of the young embryo. The embryonic
development may in tropical countries be accomplished in three weeks (see
Mantidae), but in countries where winter supervenes, the period may in some
species be extended over seven or eight months.
The external features of the post-embryonic development—a term that is more
convenient in connexion with Orthoptera than metamorphosis—are as follows:
the wings are never present when the Insect is first hatched, but appear
subsequently, and increase in size at the moults; the form and proportions
of the segments of the body—especially of the thorax—undergo much change;
an alteration of colour occurs at some of the moults, and the integument
becomes harder in the adult condition. Neither the development of the
internal organs, nor the physiological processes by which the changes of
external form are effected, appear to have been studied to any great
extent.
Many of the Orthoptera do not possess wings fit for flight, and some
species even in the adult state have no trace whatever of such organs.
Flight, indeed, appears to be of minor importance in the Order; in many
cases where the wings exist they are purely musical organs, and are not of
any use for flight. The apterous and the flightless conditions are not
confined to one division of the Order, but are found in all the families
and in many of their subdivisions. As the front pair of wings in Orthoptera
do not really carry out the function of flight, and as they differ in
several particulars from the hinder pair, or true wings, it is usual to
call them tegmina. The musical powers of the Orthoptera are confined to the
saltatorial group of families.
{200}[Illustration: FIG. 101.—_Poecilimon affinis_ ♂. Bulgaria. Alar organs
serving only as musical organs. The ear on front tibia and aural orifice of
prothorax are well shown.]
The Cursoria are dumb or nearly so; it is a remarkable fact that also in
this latter division the alar organs, though frequently present, have but
little value for flight, and are in some cases devoted to what we may call
purposes of ornament or concealment. This is specially the case in the
Phasmidae and Mantidae, where the effectiveness of colour and pattern of
these parts becomes truly astonishing. The tegmina frequently exhibit an
extraordinary resemblance to vegetable structures, and this appearance is
not superficial, for it may be seen that the nervures of the wings in their
disposition and appearance resemble almost exactly the ribs of leaves. One
of the most remarkable of the features of Orthoptera is that a great
difference frequently exists between the colours of the tegmina and of the
wings, _i.e._ the front and hind wings; the latter are concealed in the
condition of repose, but when activity is entered on and they are
displayed, the individual becomes in appearance a totally different
creature. In some cases, contrary to what usually occurs in Insects, it is
the female that is most remarkable; the male in Mantidae and Phasmidae
being frequently a creature of quite inferior appearance and power in
comparison with his consort. The musical powers of the saltatorial
Orthoptera are, however, specially characteristic of the male sex. There is
evidence that these powers are of great importance to the creatures, though
in what way is far from clear. Some parts of the structures of the body are
in many of these musical species clearly dominated by the musical organs,
and are apparently specially directed to securing their efficiency. We find
in some Locustidae that the tegmina are nothing but sound-producing
instruments, while the pronotum is prolonged to form a hood that protects
them without encumbering their action. In the males of the Pneumorides,
where the phonetic organ is situated on the abdomen, this part of the body
is inflated and tense, no doubt with the result of increasing the volume
and quality of the sound. In the genus _Methone_ (Fig. 185) we find a
grasshopper whose great hind legs have no saltatorial function, and but
little power of locomotion, but act as parts of a sound-producing
{201}instrument, and as agents for protecting some parts of the body in
repose. Further particulars of these cases must be looked for in our
accounts of the different groups.
The eggs of many Orthoptera are deposited in capsules or cases; these
capsules may contain only one egg, or a great many.
The Order includes many species of Insects, though in Britain it is poorly
represented: we have only about forty species, and this small number
includes some that are naturalised. Only a few of the forty extend their
range to Scotland. A revision of the species found in Britain has recently
been made by Mr. Eland Shaw.[127] In continental Europe, especially in the
south, the species become more numerous; about 500 are known as inhabitants
of geographical Europe. In countries where the face of nature has been less
transformed by the operations of man, and especially in the tropical parts
of the world, Orthoptera are much more abundant.
The lowest number at which the species now existing on the surface of the
earth can be estimated is 10,000. This, however, is probably far under the
mark, for the smaller and more obscure species of Orthoptera have never
been thoroughly collected in any tropical continental region, while new
forms of even the largest size are still frequently discovered in the
tropics.
We shall treat the Order as composed of eight families:—
Series, _Cursoria_: hind legs but little different from the others.
{ 1. Forficulidae—Tegmina short, wings complexly folded; body
{ armed at the extremity with strong forceps.
{ 2. Hemimeridae—Apterous: head exserted, constricted behind.
{ 3. Blattidae—Coxae of the legs large, exserted, protecting
{ the lower part of the body.
{ 4. Mantidae—Front legs very large, raptorial, armed with spines.
{ 5. Phasmidae—Mesothorax large as compared with the prothorax.
Series, _Saltatoria_: hind legs elongate, formed for leaping, their
femora usually thickened.
{ 6. Acridiidae—Antennae short, not setaceous, of not more than
{ 30 joints, tarsi three-jointed.
{ 7. Locustidae—Antennae very long, setaceous, composed of a
{ large number of joints, tarsi four-jointed.
{ 8. Gryllidae—Antennae very long, setaceous, tarsi two- or
{ three-jointed.
The first five of these subdivisions are amongst the most distinct of any
that exist in the Insecta, there being no connecting links between them.
The three groups forming the {202}Saltatoria are much more intimately
allied, and should, taken together, probably have only the same taxonomic
value as any one of the other five groups.
Owing partly to the inherent difficulties of the subject, and partly to the
fragmentary manner in which it has been treated by systematists, it has
been impossible till recently to form any clear idea of the classification
of Orthoptera. During the last twenty years Henri de Saussure and Brunner
von Wattenwyl have greatly elucidated this subject. The latter of these two
distinguished naturalists has recently published[128] a revision of the
system of Orthoptera, which will be of great assistance to those who may
wish to study these Insects. We therefore reproduce from it the characters
of the tribes, placing the portion relating to each family at the end of
our sketch thereof.
FAM. I. FORFICULIDAE—EARWIGS.
(DERMAPTERA OR DERMATOPTERA OF BRAUER AND OTHERS)
_Insects of elongate form, with an imbricate arrangement of the segments
of the body; bearing at the posterior extremity a pair of callipers or
more distorted instruments. The hind wings (when present) folded in a
complex manner, and covered, except at their tips, by a pair of short
wing-covers (tegmina), of a leather-like consistence. Wingless forms are
very numerous. The young is very similar to the adult._
[Illustration: FIG. 102.—_Pygidicrana hugeli._ Java.]
Although earwigs are said to be rare in most parts of the world, yet in
Europe no Insect is better known than _Forficula auricularia_, the common
earwig, it being very abundant even in gardens and cultivated places. In
certain seasons it not unfrequently enters our houses, in which case it too
often falls a {203}victim to prejudices that have very little to justify
them. This Insect is a good type of the winged earwigs. In the parts of the
mouth it exhibits the structures usual in the Orthoptera; there is a large
labrum, a pair of maxillae, each provided with two lobes and a palpus
consisting of two very short basal joints and three longer joints beyond
these; the mandibles are strong, with curvate pointed extremities; in the
lower lip there is a ligula exposed in front of a very large mentum; it
consists of two pieces, not joined together along the middle, but each
bearing on its lateral edge a palpus with two elongate joints and a short
basal one; this lip is completed by the lingua, which reposes on the upper
face of the part, and completely overlaps and protects the chink left by
the want of union along the middle line of the external parts of the lip.
The antennae are elongate, filiform, and are borne very near the front of
the exserted head. There are rather large facetted eyes, but no ocelli. The
three segments of the thorax are distinct, the prothorax being quite free
and capable of movement independent of the parts behind it: the meso- and
meta-nota are covered by the tegmina and wings; these latter project
slightly from underneath the former in the shape of small slips, that are
often of rather lighter colour; the wing-covers are short, not extending
beyond the insertion of the hind legs, and repose flat on the back, meeting
together in a straight line along the middle. These peculiar flat,
abbreviated wing-covers, with small slips (which are portions of the folded
wings) projecting a little from underneath them, are distinctive marks of
the winged Forficulidae.
The legs are inserted far from one another, the coxae being small; each
sternum of the three thoracic segments projects backwards, forming a
peculiar long, free fold, underlapping the front part of the following
segment. The hind body or abdomen is elongate, and is formed of ten
segments; the number readily visible being two less in the female than it
is in the male. The segments are fitted together by a complex imbrication,
which admits of great mobility and distension, while offering a remarkable
power of resistance to external pressure: each segment is inserted far
forward in the interior of that preceding it, and each also consists of
separate upper and lower plates that much overlap where they meet at the
sides (see Fig. 103). The body is always terminated by a pair of horny,
pincer-like {204}processes, which are differently shaped according to the
sex of the individual.
[Illustration: FIG. 103.—Lateral view of _Forficula auricularia_ L. Female
abdomen distended showing spiracles, S, and the small 8th and 9th dorsal
plates (7 and 8 in Fig.).]
The structure of the abdomen in the earwig has given rise to considerable
discussion. In Fig. 103 we reproduce Westwood's diagram of it as seen
fully distended in a female specimen; in this state the minute spiracles
can be detected, though in the normal condition of the body they cannot be
seen, being placed on the delicate membranes that connect the chitinous
plates. Westwood's interpretation of the structure was not, however, quite
correct, as the part which he considered to be the first dorsal plate is
really the second; so that the segments numbered 7, 8, 9 in our figure are
really 8, 9, 10. The common earwig is interesting as exhibiting, in an
imperfect state, the union of the first dorsal plate of the abdomen with
the thorax; a condition which is carried to so great an extent in the
Hymenoptera as to quite obscure the nature of the parts, and which has
consequently given rise to much perplexity and discussion. We represent
this structure as seen in the common earwig in Fig. 104, where _a_
represents the pronotum, _b_ the mesonotum, _c_ the metanotum, _d_ the
first, _f_ the second abdominal segment; _e_ being a delicate membrane of
considerable size that intervenes between the two, and which is more
exposed than are the corresponding membranes connecting the subsequent
rings; a condition similar to that which is found in _Cimbex_, _Cephus_,
and some other Hymenoptera.
[Illustration: FIG. 104.—Dorsal portions of the middle segments of body of
_Forficula auricularia_ (tegmina and wings removed).]
On the under surface of the abdomen of the earwig the full number of 10
plates cannot be superficially distinguished; but it is found by dissection
that in the female the short eighth and ninth dorsal rings are joined on
the ventral aspect by a delicate membrane, while the tenth ventral is of a
less delicate {205}nature, and forms a triangular plate at the base of each
half of the forceps. Between the branches of the forceps there is a
perpendicular plate, the pygidium of Orthopterists, possibly the unpaired
terminal portion of the body seen in some embryos, and called the telson.
The pygidium is a separate sclerite, though it looks as if it were only a
portion of the large tenth dorsal plate bent downwards, and in some
descriptive works is erroneously described as being such.
[Illustration: FIG. 105.—_Chelidura dilatata_, male. Pyrenees.]
[Illustration: FIG. 106.—Tegmina and wings (visible in part or invisible)
of apterous earwigs. 1, _Chelidura_ sp.; 2, _Chelidura dilatata_; 3,
_Anisolabis moesta_; 4. _A. maritima_. _a_, First thoracic segment; _b_,
second; _c_, third; _d_, basal portion of abdomen.]
A very large number of species of Forficulidae have the organs of flight
undeveloped. Fig. 105 represents _Chelidura dilatata_, an apterous form
that is very common in the Eastern Pyrenees. The condition of the meso- and
meta-nota—the parts from which the tegmina and wings are developed, and to
which they are attached when present—is very remarkable in these forms, and
exhibits much variety. In Fig. 106 we represent the conditions of these
parts in a few apterous forms. The tegmina or the segment from which they
are developed (_b_), are seen in the shape of a plate which may extend all
across the middle and be undivided (No. 4); in which case the appearance
indicates entire absence of the tegmina; these are, on the contrary,
evidently present in the form of slips grafted one to each side of the
second thoracic segment in _Anisolabis_ (No. 3); or they may look like
short broad slips extending all across the body, and marking off a piece
frequently called a scutellum, but which is really the mesonotum (some
species of _Chelidura_, as No. 2); or, again, they may be nearly free
tegmina, somewhat similar to those of the winged forms; this is the case
with some species of _Chelidura_, as represented by No. 1. This last figure
is taken from a species from the Sierra Nevada, apparently undescribed,
allied to _C. bolivari_.
In the cases we are considering no analogous structures exist on {206}the
metanotum (the part of the body that in the winged forms bears the wings,
and which is marked _c_ in our diagrams, Fig. 106), so that the tegmina are
to all appearance less rudimentary (or vestigial) than the wings. The
metanotum forms a sort of flap, called by Fischer[129] "involucrum alarum";
he considered the part immediately behind this to be the metanotum; this
piece is, however, no doubt really part of the abdomen (_d_ in our Figure).
This is apparently the view taken by Brunner.[130] The structure of these
parts is important as bearing on the subject of the nature and origin of
Insects' wings, a question to which no satisfactory answer has yet been
given. The appearances we have remarked on are to some extent similar to
the conditions existing in the immature state of the organs of flight in
the common earwig (see Fig. 112, p. 212), but whether the varieties
presented by the wingless forms have parallels in the immature conditions
of the various winged forms is quite uncertain, the life-histories of
earwigs being almost unknown.
[Illustration: FIG. 107.—Wing of _Forficula auricularia_. A, Wing expanded,
explanation in text; B, wing folded and packed.]
The developed wings of earwigs are worthy of attention, both as regards
their actual structure and the manner in which they are folded up in
repose. When expanded they have a shape curiously suggestive of the human
ear. The chief parts of the wing, as shown in Fig. 107, A, are _a_, _b_,
two portions of the horny piece that forms the scale which covers the more
delicate parts of the wing when it is folded, and which, according to
Brunner, represents the radial and ulnar fields of the wings of Acridiidae
and Locustidae (see Fig. 167); _c_ is the small apical field limited below
by the vena dividens; _d_ is the vena plicata which runs along the under
side of the scale as far as the apical field, where it gives off the
axillary nerves; _e_ is a vena spuria, or adventitious vein such as exists
in many other Orthoptera with delicate wings. On the front part of the
scale, _a_, and on a different plane so that it is not shown in our figure,
there is a very delicate small band which is supposed to {207}represent the
marginal field of the wing of other Orthoptera. There are, however, grave
difficulties in the way of accepting this view of the earwig's wing,
amongst which we may mention the position of the vena dividens and its
relation to the so-called radial and ulnar fields of the wing. The wings
are remarkable for their delicacy; moreover, the way in which they fold up
so as to be packed in the manner shown in B, Fig. 107, is very interesting,
there being, in fact, no other Insects that fold up their wings in so
complicated and compact a fashion as the earwigs do. The process is carried
out somewhat as follows: the longer radii come a little nearer together,
the delicate membrane between them falling into folds somewhat like those
of a paper fan; a transverse fold, or turn-over, then occurs at the point
where the radii, or axillary nerves, start from the vena plicata; then a
second transverse fold, but in a reversed direction, occurs affecting the
wing just close to the spots where the shorter radial nervures are dilated;
then by a contraction close to the scale the whole series of complex folds
and double are brought together and compressed.
It is quite a mystery why earwigs should fold their wings in this complex
manner, and it is still more remarkable that the Insects very rarely use
them. Indeed, though _Forficula auricularia_ is scarcely surpassed in
numbers by any British Insect, yet it is rarely seen on the wing; it is
probable that the majority of the individuals of this species may never
make use of their organs of flight or go through the complex process of
unfolding and folding them. It should be remarked that no part of the
delicate membranous expanse of the wing is exposed when the wings are
packed in their position of repose; for the portion that projects from
under the tegmina—and which, it will be remembered, is always present, for
when wings exist in earwigs they are never entirely concealed by the
tegmina—is, it is curious to note, of hard texture, and is frequently
coloured and sculptured in harmony with the tegmen; in fact, one small part
of the wing forms in colour and texture a most striking contrast to the
rest of the organ, but agrees in these respects with the wing-covers. This
condition is seen in Fig. 108, where B shows the sculpture of the tegmina
_t_, and of the projecting tips of the wings _w_. There are numerous other
instances in Orthoptera where one part of a wing or wing-case {208}is
exposed and the other part concealed, and the exposed portion is totally
different in colour and texture from the concealed portion.
The wings of earwigs are attached to the body in a very unusual manner;
each wing is continued inwards on the upper surface of the metanotum, as if
it were a layer of the integument meeting its fellow on the mesial line;
the point of contact forming two angles just behind the metanotum.
Some writers have considered that the tegmina of earwigs are not the
homologues of those of other Orthoptera, but are really tegulae (cf. Fig.
56, p. 103). We are not aware that any direct evidence has been produced in
support of this view.
The pair of forceps with which the body is armed at its extremity forms
another character almost peculiar to the earwigs, but which exists in the
genus _Japyx_ of the Thysanura. These forceps vary much in the different
genera of the family; they sometimes attain a large size and assume very
extraordinary and distorted shapes. They are occasionally used by the
Insects as a means of completing the process of packing up the wings, but
in many species it is not probable that they can be used for this purpose,
because their great size and peculiarly distorted forms render them
unsuitable for assisting in a delicate process of arrangement; they are,
too, always present in the wingless forms of the family. Their importance
to the creature is at present quite obscure; we can only compare them with
the horns of Lamellicorn Coleoptera, which have hitherto proved
inexplicable so far as utility is concerned. No doubt the callipers of the
earwigs give them an imposing appearance, and may be of some little
advantage on this account; they are not known to be used as offensive
instruments for fighting, but they are occasionally brought into play for
purposes of defence, the creatures using them for the infliction of nips,
which, however, are by no means of a formidable character.
[Illustration: FIG. 108.—_Anechura scabriuscula._ Himalaya. A, Outline of
the Insect; B, tegmina, _t_, and tips of wings, _w_, showing their similar
sculpture.]
{209}These forceps are, in the case of the common earwig—and they have not
been studied from this point of view in any other species—remarkable,
because of the great variation in their development in the male, a
character which again reminds us of the horns of Lamellicorn beetles: in
the female they are comparatively invariable, as is also the case in the
few species of Lamellicornia, which possess horned females. A and B in
Figure 109 represent the forceps of different males of the common earwig, C
showing those of the other sex. The subject of the variation of the male
callipers of the earwig has been considered by Messrs. Bateson and
Brindley,[131] who examined 1000 specimens captured on the same day on one
of the Farne islands off the coast of Northumberland; 583 of these were
mature males, and the pincers were found to vary in length from about 2½
mm. to 9 mm. (A and B in Fig. 109 represent two of the more extreme forms
of this set of individuals.) Specimens of medium size were not, as it might
perhaps have been expected they would be, the most common; there were, in
fact, only about 12 individuals having the forceps of the medium length—4¾
to 5¼ mm., while there were no less than 90 individuals having forceps of a
length of about 7 mm., and 120 with a length of from 2¾ to 3¼. Males with a
medium large length of the organ and with a medium small length thereof
were the most abundant, so that a sort of dimorphism was found to exist.
Similar relations were detected in the length of the horns of the male of a
Lamellicorn beetle examined by these gentlemen. In the case of the set of
earwigs we have mentioned, very little variation existed in the length of
the forceps in the female sex.
[Illustration: FIG. 109.—Forceps of the common earwig: A, of large male; B,
of small male; C, of female.]
In many earwigs—including _F. auricularia_—there may be seen on each side
of the dorsal aspect of the true fourth, or of the fourth and neighbouring
segments of the hind body a small elevation, called by systematists a plica
or fold, and on examination the fold will be found to possess a small
orifice on its posterior aspect. These folds are shown in Figs. 105 and
108; {210}they have been made use of for purposes of classification, though
no functional importance was attached to them. Meinert, however,
discovered[132] that there are foetid glands in this situation, and
Vosseler has recently shown[133] that the folds are connected with
scent-glands, from which proceed, in all probability, the peculiar odour
that is sometimes given off by the earwig. The forms destitute of the
folds, e.g. _Labidura_, are considered to have no scent glands. There is a
very peculiar series of smooth marks in the earwigs on the dorsal aspect of
the abdominal segments, and these are present in the glandless forms as
well as in the others.
The internal anatomy has been to some extent investigated by Dufour and
Meinert. Dufour dissected _F. auricularia_ and _Labidura riparia_, and
found[134] that salivary glands exist in the latter Insect (called by him
_Forficula gigantea_), though he was unable to discover them in the common
earwig. According to Meinert,[135] there are, however, salivary glands
affixed to the stipes of the maxillae in _F. auricularia_, while (in
addition?) _L. riparia_ possesses very elongate glands seated in the middle
or posterior part of the breast. The alimentary canal is destitute of
convolutions, but oesophagus, crop, and gizzard all exist, and the
intestine behind the stomach consists of three divisions. The Malpighian
tubes are numerous, 30 or 40, and elongate. The respiratory system is not
highly developed. Earwigs—the European species at least—have, as already
mentioned, very small powers of flight; the tracheal system is
correspondingly small, and is destitute of the vesicular dilatations that
are so remarkable in the migratory Locusts.
[Illustration: FIG. 110.—_Labidura riparia_, male. Europe.]
The three thoracic spiracles[136] are readily observed in living
{211}individuals. There are seven pairs of abdominal spiracles, which,
however, are very minute, and can only be found by distending the body as
shown in Fig. 103. The ventral chain consists of nine ganglia (the
sub-oesophageal centre is not alluded to by Dufour); the three thoracic are
equidistant and rather small; the hindmost of the six abdominal ganglia is
considerably larger than any one of the other five.
The ovaries of _Labidura riparia_ and _Forficula auricularia_ are extremely
different. In _L. riparia_ there are on each side five tubes, each
terminating separately in an obliquely directed lateral part of the
oviduct. In _F. auricularia_ there is but one tube on each side, but it is
covered by three longitudinal series of very short sub-sessile, grape-like
bodies, each of the two tubes being much dilated behind the point where
these bodies cease.
The testes in earwigs are peculiar and simple; they consist, on each side,
of a pair of curvate tubular bodies, connected at their bases and prolonged
outwards in the form of an elongate, slender vas deferens. The structures
in the males of several species have been described at some length by
Meinert,[137] who finds that in some species a double ejaculatory duct
exists.
[Illustration: FIG. 111.—Ovaries of _Labidura riparia_, A; and _Forficula
auricularia_, B. (After Dufour.)]
The young is similar to the adult in form; in the winged forms it is always
easy to distinguish the adult by the full development of the wings, but in
the wingless forms it can only be decided with certainty that a specimen is
not adult by the softer and weaker condition of the integuments. Scarcely
anything appears to be known as to the life-history, except a few
observations that have been made on the common earwig; Camerano found[138]
that this Insect has certainly three ecdyses, and possibly {212}an earlier
one which he failed to notice, and his observation confirms the vague
previous statement of Fischer. The eggs, in the neighbourhood of Turin, are
deposited and hatched in the early spring; in one case they were laid on
the 10th March, and the Insects issuing from them had completed their
growth and were transformed into perfect Insects on the 22nd May. In the
immature state the alar structures of the future imago may be detected. The
tegmina-bearing sclerites, _t_, Fig. 112, look then somewhat like those of
some of the apterous forms (Fig. 106) and, as shown in A and B, Fig. 112,
do not differ greatly in the earlier and later stages. The wings, however,
change much more than the tegmina do; at first (Fig. 112, A) there is but
little difference between the two, though in the interior of the wing-flap
some traces of a radiate arrangement can be seen, as shown at _W_ in A,
Fig. 112; in a subsequent condition the wing-pads are increased in size and
are more divided, the appearance indicating that the wings themselves are
present and packed about a centre, as shown in _W_ of B, Fig. 112.
[Illustration: FIG. 112.—Notal plates from which the tegmina and wings of
_Forficula auricularia_ are developed in young, A, and more advanced, B,
nymph.]
In the young of the common earwig the number of joints[139] in the antennae
increases with age. Camerano, _l.c._, says that before emergence from the
egg there are apparently only 8 joints in the antennae, and Fischer states
that the larvae of _F. auricularia_ have at first only 8 antennal joints;
later on 12 joints are commonly found, and, according to Bateson,[140] this
number occasionally persists even in the adult individual. Meinert
says[141] that the newly hatched _Forficula_ has either 6 or 8 joints, and
he adds that in the later portion of the preparatory stage the number is
12. Considerable discrepancy prevails in books as to the normal number of
joints in the antennae of the adult _F. auricularia_, the statements
varying from 13 to 15. The latter number may be set aside as erroneous,
although it is, curiously {213}enough, the one given in the standard works
of Fischer, Brunner, and Finot. Meinert gives without hesitation 14 as the
number; Bateson, _l.c._, found that 14 joints occurred in 70 or 80 per cent
of adult individuals, that 13 was not uncommon, that 12 or 11 occasionally
occurred, and that the number may differ in the two antennae of the same
individual. These variations, which seem at first sight very remarkable,
may with probability be considered as due to the fact that in the young
state the number of joints increases with age, and that the organs are so
fragile that one or more of the joints is very frequently then lost, the
loss being more or less completely repaired during the subsequent
development. Thus a disturbing agency exists, so that the normal number of
14 joints is often departed from, though it appears to be really natural
for this species. Bateson has also pointed out that when the normal number
of articulations is not present, the relative proportions of joints 3 and 4
are much disturbed. It is, however, probable that the increase in number of
the joints takes place by division of the third or third and fourth joints
following previous growth thereof, as in Termitidae; so that the
variations, as was suggested by Bateson, may be due to mutilation of the
antennae, and consequent incompletion of the normal form of the parts from
which the renovation takes place; growth preceding segmentation—in some
cases the growth may be like that of the adult, while the segmentation
remains more incomplete. In the young the forceps of the two sexes differ
but slightly; the form of the abdominal rings is, on the contrary,
according to Fischer, already different in the two sexes in the early
stage.
The common earwig has a very bad reputation with gardeners, who consider it
to be an injurious Insect, but it is probable that the little creature is
sometimes made the scapegoat for damage done by other animals; it appears
to be fond of sweets, for it often makes its way to the interior of fruits,
and it no doubt nibbles the petals, or other delicate parts of flowers and
vegetables. Camerano, however, states, _l.c._, that the specimens he kept
in confinement preferred dead Insects rather than the fruits he offered
them. Rühl considers the earwig to be fond of a carnivorous diet, eating
larvae, small snails, etc., and only attacking flowers when these
fail.[142] It has a great propensity for concealing {214}itself in places
where there is only a small crevice for entry, and it is possible that its
presence in fruits is due to this, rather than to any special fondness for
the sweets. This habit of concealing itself in chinks and crannies in
obscure places makes it an easy matter to trap the Insect by placing pieces
of hollow stalks in the situations it affects; inverted flower-pots with a
little hay, straw, or paper at the top are also effectual traps. We have
remarked that it is very rarely seen on the wing, and though it has been
supposed to fly more freely at night there is very little evidence of the
fact. Another British species, _Labia minor_, a smaller Insect, is,
however, very commonly seen flying.
Earwigs have the reputation of being fond of their young, and Camerano
describes the female of the common earwig as carefully collecting its eggs
when scattered, lifting them with its mandibles and placing them in a heap
over which it afterwards brooded. De Geer[143] more than a century ago
observed a fondness of the mother for the young. After the eggs were
hatched, Camerano's individual, however, evinced no interest in the young.
A larger species, _Labidura riparia_ (Fig. 110) is said to move its eggs
from place to place, so as to keep them in situations favourable for their
development.
The name "earwig" is said to be due to an idea that these creatures are
fond of penetrating into the ears of persons when asleep. Hence these
Insects were formerly much dreaded, owing to a fear that they might
penetrate even to the brain. There does not appear to be on record any
occurrence that could justify such a dread, or the belief that they enter
the ears. If they do not do so, it is certainly a curious fact that a
superstition of the kind we have mentioned occurs in almost every country
where the common earwig is abundant; for it has, in most parts of Europe, a
popular name indicating the prevalence of some such idea. It is known as
_Ohren-wurm_ in German, as _perce-oreille_ in French, and so on. The
expanded wing of the earwig is in shape so very like the human ear, that
one is tempted to suppose this resemblance may in former ages have given
rise to the notion that the earwig has some connexion with the human ear;
but this explanation is rendered very improbable by the fact that the
earwig is scarcely ever seen with its wings expanded, and that it is a most
difficult matter to unfold them {215}artificially, so that it is very
unlikely that the shape of the wings should have been observed by untutored
peoples.
The group Forficulidae seems to be most rich in species in warm and
tropical regions; several unwinged species are met with in the mountainous
districts of Europe; indeed, in some spots their individuals are extremely
numerous under stones. In Britain we have a list of six species, but only
two of these are to be met with; the others have probably been introduced
by the agency of man, and it is doubtful whether more than one of these
immigrants is actually naturalised here. One of these doubtfully native
species is the fine _Labidura riparia_ (Fig. 110), which was formerly found
near Bournemouth. Altogether about 400 species of earwigs are known at the
present time, and as they are usually much neglected by Insect collectors,
it is certain that this number will be very largely increased, so that it
would be a moderate estimate to put the number of existing species at about
2000 or 3000. None of them attain a very large size, _Psalis americana_
being one of the largest and most robust of the family; a few display
brilliant colours, and some exhibit a colour ornamentation of the surface;
there are two or three species known that display a general resemblance to
Insects of other Orders. The remarkable earwig represented in Fig. 102 (and
which appears to be a nondescript form—either species or variety—closely
allied to _P. marmoricauda_) was found by Baron von Hügel on the mountains
of Java; the femora in this Insect have a broad face which is turned
upwards instead of outwards, the legs taking a peculiar position; and it is
curious that this exposed surface is ornamented with a pattern. The feature
that most attracts attention on inspecting a collection of earwigs is,
however, the forceps, and this is the most marked collective character of
the group. These curious organs exhibit a very great variety; in some cases
they are as long as the whole of the rest of the body, in others they are
provided with tynes; sometimes they are quite asymmetrical, as in
_Anisolabis tasmanica_ (Fig. 113); in _Opisthocosmia cervipyga_, and many
others they are curiously distorted in a variety of ways. The
classification of the earwigs is still in a rudimentary state; the number
of joints in the antennae, the form of the feet, and (in the terrestrial
forms) the shape of the rudimentary wing-cases and wings being the
characters that have been made most use of by {216}systematists; no
arrangement into sub-families or groups of greater importance than genera
is adopted.
The only particulars we have as to the embryological development of the
earwig are due to Heymons.[144] The forceps spring from the eleventh
abdominal segment, and represent the cerci of other Orthoptera. An
egg-tooth is found to be present on the head for piercing the egg-shell.
The embryo reverses its curved position during the development, as other
Orthoptera have been observed to do, but in a somewhat different manner,
analogous to that of the Myriapods.
Several fossil Forficulidae are known; specimens belonging to a peculiar
genus have been described from the Lower Lias of Aargau and from the
Jurassic strata in Eastern Siberia, but the examples apparently are not in
a very satisfactory state of preservation. In the Tertiary formations
earwigs have been found more frequently. Scudder has described eleven
species of one peculiar genus from the Lower Miocene beds at Florissant in
Colorado; some of these specimens have been found with the wings expanded,
and no doubt that they were fully developed Forficulidae can exist. The
fossil species of earwigs as yet known do not display so remarkable a
development of the forceps as existing forms do.
[Illustration: FIG. 113.—_Anisolabis tasmanica_ ♂.]
Brauer and others treat the Forficulidae as a separate Order of
Insects—Dermaptera—but the only structural characters that can be pointed
out as special to the group are the peculiar form of the tegmina and hind
wings—which latter, as we have said on p. 206, are considered by some to be
formed on essentially the same plan as those of other Orthoptera—the
imbrication of the segments, and the forceps terminating the body. The
development, so far as it is known, is that of the normal Orthoptera. Thus
the Forficulidae are a very distinct division of Orthoptera, the characters
that separate them being comparatively slight, though there are no
intermediate forms. Some of those who treat the Dermaptera as a sub-Order
equivalent to the rest of the divisions of the Order, call the latter
combination Euorthoptera.
{217}FAM. II. HEMIMERIDAE.
_Apterous, blind Insects with exserted head, having a constricted neck,
mouth placed quite inferiorly; the thoracic sterna large, imbricate. Hind
body elongate, the segments imbricate, the dorsal plates being large and
overlapping the ventral; the number of visible segments being different
according to sex: a pair of long unsegmented cerci at the extremity.
Coxae small, widely separated. Development intra-uterine._
[Illustration: Fig. 114.—_Hemimerus hanseni_, female. Africa. (After
Hansen.)]
[Illustration: FIG. 115.—Under side of head and front of prothorax of
_Hemimerus_. _a_, base of antenna; _b_, articulation of antenna; _c_,
labrum; _d_, mandible; _e_, condyle of mandible; _f_, articular membrane of
mandible; _g_, stipes of maxilla; _h_, exterior lobe; _i_, palpus of
maxilla; _k_, submentum; _l_, mentum; _m_, terminal lobe of labium; _n_,
labial palp; _o_, plate between submentum and sternum; _p_, prosternum;
_q_, cervical sclerites. (After Hansen.)]
In describing the labium of Mandibulata, p. 97, we alluded to the genus
_Hemimerus_ as reputed to possess a most peculiar mouth. When our remarks
were made little was known about this Insect; but a very valuable
paper[145] by Dr. H. J. Hansen on it has since appeared, correcting some
errors and supplying us with information on numerous points. M. de Saussure
described the Insect as possessing two lower lips, each bearing articulated
palpi, and he therefore proposed to treat _Hemimerus_ as the representative
of a distinct Order of Insects, to be called Diploglossata. It now appears
that the talented Swiss entomologist was in this case deceived by a bad
preparation, and that the mouth shows but little departure from the
ordinary mandibulate type. There is a large inflexed labrum; {218}the
mandibles are concealed by the maxillae, but are large, compressed, and on
their inner edge toothed. The maxillae are well developed, are surmounted
by two lobes and bear five-jointed palpi. The ligula appears to be broad
and short, and formed of two parts longitudinally divided; the short palpi
consist of three segments. The mentum is very large. The lingua is present
in the form of a free pubescent lobe with a smaller lobe on each side. The
structure of the pleura is not fully understood; that of the abdomen seems
to be very like the earwigs, with a similar difference in the sexes. The
cerci are something like those of Gryllidae, being long, flexible, and
unsegmented. The legs have rather small coxae, and three-jointed tarsi, two
of which are densely studded with fine hairs beneath, as in Coleoptera. It
is difficult to detect the stigmata, but Dr. Hansen believes there are ten
pairs.
[Illustration: FIG. 116.—Foetus of _Hemimerus_. (After Hansen.) _a_,
Antenna; _b_, organ from the neck; _c_, cerci; _d_, membrane (? cast
skins).]
[Illustration: FIG. 117.—_Hemimerus talpoides_. Africa. (After de
Saussure.) A, Upper; B, under surface.]
The species described by Dr. Hansen as _H. talpoides_ is probably distinct
from that of Walker, though both come from equatorial West Africa. Dr.
Hansen's species, which may be called _H. hanseni_, has been found living
on the body of a large rat, _Cricetomys gambianus_; the Insect occurred on
a few specimens only of the mammal, but when found was present in
considerable numbers; it runs with rapidity among the hairs and apparently
also springs. The nature of its food is by no means clear. Not the least
remarkable fact in connexion with this peculiar Insect is its gestation.
The young are borne inside the mother, {219}apparently about six at a time,
the larger one being of course the nearest to the orifice. Dr. Hansen
thinks the young specimens are connected with the walls of the maternal
passages by means of a process from the neck of each. But the details of
this and other points are insufficiently ascertained; it is, indeed,
difficult to understand how, with a process of the kind of which a fragment
is shown in Fig. 116, _b_, the Insect could fix itself after a detachment
for change of position. The young is said to be very like the adult, but
with a simpler structure of the antennae and abdomen. On the whole, it
appears probable that _Hemimerus_ is, as stated by Dr. Hansen, a special
family of Orthoptera allied to Forficulidae; further information both as to
structure and development are, however, required, as the material at the
disposition of the Swedish entomologist was very small.
{220}CHAPTER IX
ORTHOPTERA CONTINUED—BLATTIDAE, COCKROACHES
FAM. III. BLATTIDAE—COCKROACHES.
_Orthoptera with the head deflexed, in repose concealed from above, being
flexed on to the under-surface with the anterior part directed backwards.
All the coxae large, free, entirely covering the sternal surfaces of the
three thoracic segments, as well as the base of the abdomen. The sternal
sclerites of the thoracic segments little developed, being weak and
consisting of pieces that do not form a continuous exo-skeleton; tegmina
and wings extremely variable, sometimes entirely absent. The wings
possess a definite anal region capable of fan-like folding; rarely the
wing is also transversely folded. The three pairs of legs differ but
little from one another._
[Illustration: FIG. 118.—_Heterogamia aegyptiaca_. A, male; B, female.
(After Brunner.)]
The Blattidae, or cockroaches, are an extensive family of Insects, very
much neglected by collectors, and known to the ordinary observer chiefly
from the fact that a few species have {221}become naturalised in various
parts of the world in the houses of man. One such species is abundant in
Britain, and is the "black beetle" of popular language; the use of the word
beetle in connexion with cockroaches is, however, entomologically
incorrect. One or two members of the family are also well known, owing to
their being used as the "corpora vilia" for students commencing anatomical
investigation of the Arthropoda; for this purpose they are recommended by
their comparatively large size and the ease with which an abundant supply
of specimens may always be procured, but it must be admitted that in some
respects they give but a poor idea of Insect-structure, and that to some
persons they are very repulsive.
The inflexed position of the head is one of the most characteristic
features of the Blattidae; in activity it is partially released from this
posture, but the mouth does not appear to be capable of the full extension
forwards that is found in other Insects that inflex the head in repose. The
labium is deeply divided, the lingua forms a large lobe reposing on the
cleft. The maxillary palpi have two basal short joints, and three longer
joints beyond these; the labial palps consist of three joints of moderate
length. The under-surface of the head is formed in large part by the
submentum, which extends back to the occipital foramen.
[Illustration: FIG. 119.—Under-surface of _Periplaneta australasiae_. _c_,
Coxae.]
The front of the head is the aspect that in repose looks directly
downwards; the larger part of it is formed by the clypeus, which is
separated from the epicranium by a very fine suture angulate in the middle;
there is a large many-facetted eye on each side; near to the eye a circular
space serves for the insertion of the antenna; close to this and to the eye
there is a peculiar small area of paler colour, frequently membranous,
called the fenestra, and which in the males of _Corydia_ and
{222}_Heterogamia_ is replaced by an ocellus. The antennae are very
elongate and consist of a large number of minute rings or joints,
frequently about 100. The head is not inserted directly in the thorax, as
is the case in so many Insects; but the front of the thorax has a very
large opening, thus the neck between it and the head is of more than usual
importance; it includes six cervical sclerites.
The pronotum is more or less like a shield in form, and frequently entirely
conceals the head, and thus looks like the most anterior part of the body;
usually it has no marked angles, but in some of the apterous forms the hind
angles are sharp and project backwards. In contrast to the pronotum the
prosternum is small and feeble, and consists of a slender lateral strip on
each side, the two converging behind to unite with a median piece, the
prosternum proper. None of these pieces of the ventral aspect of the
prothorax are ordinarily visible, the side-pieces being covered by the
inflexed head, and the median piece by the great coxae. In some of the
winged Blattidae (_Blabera_, e.g.) there is at the base of each anterior
coxa a small space covered by a more delicate membrane, that suggests the
possibility of the existence of a sensory organ there (Fig. 120, _i_).[146]
At the base of—above and behind—the front coxa the prothoracic spiracle is
situate.
[Illustration: FIG. 120.—Base of front leg and portion of prothorax of
_Blabera gigantea_. _a_, Under-side of pronotum; _b_, fold of pronotum?;
_c_, epimeron?; _d_, episternum?; _e_, trochantin; _f_, coxa; _g_,
trochanter; _h_, base of femur; _i_, presumed sense organ.]
The meso- and meta-thoracic segments differ but slightly from one another;
the notal or dorsal pieces are moderately large, while the sternal or
ventral are remarkably rudimentary, and are frequently divided on the
middle line. Connected with the posterior part of each sternum there is a
piece, bent upwards, called by some anatomists the furca; when the sterna
are divided the furca may extend forwards between them; in other {223}cases
it is so obscure externally as to leave its existence in some doubt.
The sterna in Blattidae are remarkable for their rudimentary structure.
This is probably correlated with the great development of the coxae, which
serve as shields to the lower part of the body. The pieces of the sterna
are not only small, but are also of feeble consistence—semi-membranous, in
fact—and appear like thicker portions of the more extensive and delicate
membrane in which they are situate; they sometimes differ considerably in
the sexes of the same species. The coxae have very large bases, and between
them and the sterna are some pieces that are grooved and plicate, so that
it is not easy to decide as to their distinctions and homology (Fig. 120).
The second breathing orifice is a slit placed in a horny area in the
membrane between the middle and hind coxae.
The legs are remarkable for the large and numerous spines borne by the
tibiae, and frequently also by the femora: the trochanters are distinct and
of moderate size; the tarsi are five-jointed, frequently the basal four
joints are furnished with a pad beneath; the fifth joint is elongate, bears
two claws, and frequently between these a projecting lobe or arolium; this
process scarcely exists in the young of _Stilopyga orientalis_, the common
cockroach, though it is well developed in the adult. The hind body or
abdomen is always large, and its division into rings is very visible, but
the exact number of these that can be seen varies according to age, sex,
species, and to whether the dorsal or ventral surface be examined. The
differences are chiefly due to the retraction and inflexion of the apical
segments; the details of the form of these parts differ in nearly every
species. It is, however, considered that ten dorsal and ventral plates
exist, though the latter are not so easily demonstrated as the former. The
basal segment is often much diminished, the first dorsal plate being
closely connected with the metanotum, while the first ventral may be still
more rudimentary; much variety exists on this point. In the female two of
the ventral terminal plates are frequently inflexed, so as to be quite
invisible without dissection. From the sides of the tenth segment spring
the cerci, flat or compressed processes very various in size, length, and
form, usually more or less distinctly jointed. Systematists call the
seventh ventral plate of the {224}female the "lamina subgenitalis," or the
"lamina subgenitalis spuria," the concealed eighth plate being in this
latter case considered the true subgenital plate. In the male this term is
applied to the ventral plate of the ninth segment, the corresponding dorsal
plate being called the "lamina supra-analis." These terms are much used in
the systematic definitions of the genera and larger groups.
The males, in addition to the cerci alluded to as common to both sexes, are
provided on the hind margin of the lamina subgenitalis with a pair of
slender styles. These are wanting in the females, but in the common
cockroach the young individuals of that sex are provided, like the male,
with these peculiar organs. M. Peytoureau has described[147] the mode of
their disappearance, viz. by a series of changes at the ecdyses.
Cholodkovsky, who has examined the styles, considers them to be
embryologically the homologues of true legs.[148] These styles are said not
to be present in any shape in some species—_Ectobia_, _Panesthia_, etc.;
this probably refers only to the adults. In some cases a curious condition
occurs, inasmuch as one of the two styles is absent, and is replaced by a
notch on the right side, thus causing an asymmetry—_Phyllodromia_,
_Temnopteryx_, etc.
It has been found in several species that there are eight pairs of
abdominal spiracles, making, with the two thoracic, ten pairs in all. The
first of the abdominal spiracles is larger than the others, and in the
winged species may be easily detected by raising the tegmina and wings, it
being more dorsal in position than those following, which are in some
species exposed on the ventral surface owing to the cutting away of the
hind angles of the ventral plates; but the terminal spiracles are in all
cases difficult to detect, and it is possible that the number may not be
the same in all the species of the family. The cerci exhibit a great deal
of variety. In the species with elongate tegmina and wings the cerci are
elongate, and are like antennae in structure; in many of the purely
apterous forms the cerci appear to be entirely absent (cf. Fig. 130,
_Gromphadorhina_), but on examination may be found to exist in the form of
a small plate, or papilla scarcely protuberant. In the males of
_Heterogamia_ they are, on the {225}contrary, very like little antennae; in
the unwinged females of this genus they are concealed in a chink existing
on the under-surface of the apex of the body.
The alar organs of Blattidae are of considerable interest from several
points of view. They exist in various conditions as regards size and
development, and in some forms are very large; each tegmen in some species
of the genus _Blabera_ (Fig. 132) may attain a length of nearly three
inches; in other cases wings and tegmina are entirely absent, and various
intermediate conditions are found. In Fig. 121 we give a diagram of the
tegmen or front wing, A, and the hind wing, B, to explain the principal
nervures and areas. The former are four in number, and, adopting Brunner's
nomenclature[149] for them, are named proceeding from before backwards
mediastinal, _a_; radial, _b_; infra-median (or ulnar), _c_; and dividens,
_d_. An adventitious vein, vena spuria, existing in the hind wings of
certain genera is marked _sp_ in B.
[Illustration: FIG. 121.—Diagram of tegmen, A, and wing, B, in Blattidae.
Nervures: _a_, mediastinal; _b_, radial; _c_, ulnar or infra-median; _d_,
dividens; _sp_, spuria. Areas: 1, mediastinal or marginal; 2, scapular or
radial; 3, median; 4, anal or axillary.]
The vena dividens is of great importance, as it marks off the anal or
axillary field, which in both tegmen and wing has a different system of
minor veins from what obtains in the rest of the organ; the veins being in
the anterior region abundantly branching and dichotomous (Fig. 132), while
in the anal field there is but little furcation, though the nervures
converge much at the base. The mediastinal gives off minor veins towards
the front only, the radial gives off veinlets at first towards the front,
but nearer the tip of the wings sends off minor veins both backwards and
forwards. The infra-median or ulnar vein is very variable; it is frequently
{226}abbreviated, and on the whole is of subordinate importance to the
other three. These latter thus form four chief areas or fields, viz.—1,
mediastinal or marginal; 2, scapular or radial; 3, median; and 4, anal.
These nervures and divisions may be traced in a large number of existing
and fossil Blattidae, but there are forms existing at present which it is
difficult to reduce to the same plan. In _Euthyrhapha_, found in the
Pacific Islands, the hind wings are long and project beyond the tegmina,
and have a very peculiar arrangement of the nervures; the species of
_Holocampsa_ also possess abnormal alar organs, while the structure of
these parts in _Diaphana_ (Fig. 122) is so peculiar that Brunner wisely
refrains from attempting to homologise their nervures with those of the
more normal Blattidae. The alar organs are frequently extremely different
in the two sexes of the same species of Blattidae, and the hind wing may
differ much from the tegmen as regards degree of departure from the normal.
So that it is not a matter for surprise that the nervures in different
genera cannot be satisfactorily homologised.
[Illustration: FIG. 122.—_Diaphana fieberi._ Brazil. A, The Insect, natural
size; B, tegmen, and C, wing, magnified. (After Brunner.)]
But the most peculiar wings in the family are the folded structures found
in some forms of the groups Ectobiides and Oxyhaloides [Anaplectinae and
Plectopterinae of de Saussure]. These have been studied by de
Saussure,[150] and in Fig. 123 we reproduce some of his sketches, from
which it will be seen that in B and C the wing is divided by an unusual
cross-joint into two parts, the apical portion being also longitudinally
divided into two pieces _a_ and _b_. Such a form of wing as is here shown
has no exact parallel in any of the other groups of Insects, though the
earwigs and some of the Coleoptera make an approach to it. This structure
permits a very perfect folding of the wing in repose. The peculiarities
exhibited have been explained by de Saussure somewhat as follows. In the
ordinary condition of Orthoptera the axillary or anal field (P) when the
wings are {227}closed collapses like a fan, and also doubles under the
anterior part (H) of the wing along the line _a a_, in Fig. 123, A, the
result being similar to that shown by our Fig. 124. It will be noticed in
Fig. 123, A, that a small triangular area (_t_) exists at the tip of the
wing just where the fold takes place, so that when the wing is shut this
little piece is liberated, as shown in _t_, Fig. 124. In many Blattidae,
e.g. _Blabera_ (Fig. 132), no trace of this little intercalated piece can
be found, but in others it exists in various degrees of development
intermediate between what is shown in _Thorax porcellana_ (Fig. 123, A) and
in _Anaplecta azteca_ (123, B), so that _a_, _b_ of the latter may be
looked on as a greater development of the condition shown in A at _t_. It
will be noticed that the superadded part of the wing of 123, B, possesses
no venation, being traversed only by the line along which it folds; but in
the wing of _Diploptera silpha_, 123, C, the corresponding part is
complexly venated. This venation, as Brunner says,[151] is not an extension
of the ordinary venation of the wing, but is _sui generis_. It is curious
that though all the degrees of development between A and B exist in various
forms of the tribes Ectobiides and Oxyhaloides, yet there is nothing to
connect the veined apex of Diploptera with the unveined one of _Anaplecta_.
[Illustration: FIG. 123.—Hind wings of Blattidae. A, _Thorax porcellana_;
B, _Anaplecta azteca_; C, _Diploptera silpha_. (After de Saussure.)]
[Illustration: FIG. 124.—Hind wing of _Blatta_ folded. _t_, Free triangular
area. (After de Saussure.)]
The internal anatomy of Blattids has been investigated in only one or two
species. There are no great peculiarities, but some features of minor
interest exist. The alimentary canal (Fig. 125) is remarkable {228}on
account of the capacious crop, and the small gut-like, chylific ventricle;
eight elongate pouches are situate on this latter part at its junction with
the gizzard.
The Malpighian tubules are very numerous and delicate; there are extensive
salivary glands and reservoirs; and on the anterior part of the true
stomach there are eight caecal diverticula. The great chain of the nervous
system consists in all of eleven ganglia—two cephalic, three thoracic, and
six abdominal.
The ovaries in _Stilopyga orientalis_ consist each of eight egg-tubes,
placed at the periphery of a common receptacle or oviduct, the pair of
receptacles themselves opening into a common chamber—the uterus—which is
surrounded by a much branching serific or colleterial gland. In this
chamber the egg-case is formed from the secretion of the gland just
mentioned. According to Miall and Denny,[152] there is a spermatheca which
opens not into the uterus but into the cloacal chamber behind it. Lowne
doubts this diverticulum being a true spermatheca. The manner in which the
eggs are fertilised and their capsule modelled is uncertain.[153]
[Illustration: FIG. 125.—Alimentary canal of _Stilopyga orientalis_. (After
Dufour.) _a_, Head; _b_, salivary glands; _c_, salivary reservoir; _d_,
crop; _e_, diverticula placed below proventriculus; _f_, stomach; _g_,
small intestine; _h_, rectum; _i_, Malpighian tubes; _k_, extremity of hind
body.]
The internal reproductive organs of the male are very complex in _Stilopyga
orientalis_; each testis consists of a number (30 to 40) of vesicles placed
on a tube which is prolonged to form the vas deferens. There is a very
peculiar large complex gland consisting of longer and shorter utricles,
opening into the vesiculae seminales, and forming a "mushroom-shaped
gland."[154] {229}This gland is much larger than the testes proper, which,
it is said, lose early their functional activity in the species in
question, and shrivel. There is another important accessory gland, the
conglobate gland of Miall and Denny, opening on a portion of the external
copulatory armour.
Although some species of Blattidae are domesticated in our houses, and
their bodies have been dissected by a generation of anatomists, very little
is known as to their life histories. The common "black beetle" of the
kitchen is said by Cornelius to be several years in attaining the adult
state. Observations made at Cambridge by the writer, as well as others now
being carried on there by Mr. H. H. Brindley, quite confirm this view, the
extent of growth accomplished in several months being surprisingly little,
and the amount of food consumed very small. It is therefore not improbable
that the life of an individual of this species may extend to five years.
_Phyllodromia germanica_, a species that is abundant in the dwellings of
the peoples of north-eastern Europe, attains its full development in the
course of a few months.
We have already alluded to the fact that in the Blattidae the eggs are laid
in a capsule formed in the interior of the mother-Insect. This capsule is a
horny case varying much in size and somewhat less in form in the different
species; it is borne about for some time by the mother, who may not
infrequently be seen running about with it protruding from the hinder part
of the body. Sooner or later the capsule is deposited in a suitable
situation, and the young cockroaches emerge; it is said that they are
sometimes liberated by the aid of the mother. Mr. Brindley has found it
very difficult to procure the hatching of the young from their capsules.
[Illustration: FIG. 126.—Egg-capsules of European Blattidae. A, _Ectobia
lapponica_; B, _Phyllodromia germanica_; C, _Heterogamia aegyptiaca_.
(After Brunner.)]
It is known that some Blattidae are viviparous. In the case of one such
species, _Panchlora viridis_, it appears probable that the egg-capsule is
either wanting, or is present in only a very imperfect form.[155]
On emerging the young _Blatta_ is in general form very similar to the
parent, though usually much paler in colour. After casting {230}the skin
an uncertain number of times—not less than five, probably as many as
seven—it reaches the adult condition, the changes of outer form that it
undergoes being of a gradual nature, except that at the last ecdysis the
wings—in the case of the winged species—make their appearance, and the
terminal segments of the body undergo a greater change of form. What
mutations of shape may be undergone by the thoracic segments previous to
the final production of the wings has not apparently been accurately
recorded, Fischer's opinion being evidently based on very slight
observation. The little that has been recorded as to the post-embryonic
development since the observations of Hummel[156] and Cornelius[157] will
be found in the works of Brunner.[158] According to this latter authority,
in the wingless species the terminal segments of the body have the same
form in the early stages as they have in the adult state, so that this
latter condition can only be recognised by the greater hardness of the
integument. When tegmina or wings are present in a well-developed form in a
Blattid, it is certain that the Insect is adult; and when there can be seen
at the side of the mesonotum or metanotum a piece, however small, separated
by a distinct suture, it may be correctly assumed that the individual is an
adult of a species having only rudimentary alar organs. The adult female of
the common _Stilopyga orientalis_ shows this phenomenon.
The cockroaches are remarkable for the excessive rapidity with which they
run, or rather scurry, their gait being very peculiar. The common domestic
forms, when alarmed, disappear with great agility, seeking obscure corners
in which to hide themselves, it being part of their instinct to flee from
light. Hence they are called lucifugous, and are most of them entirely
nocturnal in their activities. In the South of Europe and other warmer
regions many Blattidae may, however, be found on bushes and foliage in the
daytime; these, when alarmed, fall down and run off with such speed and in
so tortuous a manner, that it is a very difficult matter to seize them. It
is recorded that the males of the genus _Heterogamia_ are attracted by
lights, though their apterous females keep themselves concealed underground
in sandy places.
{231}We may take this opportunity of alluding to the attraction that light
exerts on Insects. Many species that conceal themselves during the daytime
and shun light as if it were disagreeable, are at night-time so fascinated
by it that it is the cause of their destruction. The quantity of Insects
killed in this way by electric and other bright lights is now enormous; in
many species the individuals immolate themselves by myriads. It would
appear that only nocturnal and winged species are so attracted. So far as
we know, light has no fascination for Insects except when they are on the
wing. The phenomenon is not understood at present.
The food of Blattidae is believed to be of a very mixed character, though
Brunner considers that dead animal matter is the natural nutriment of the
members of this family. It is well known that the common cockroach eats a
variety of peculiar substances; its individuals undoubtedly have the
somewhat too economical habit of eating their own cast skins and empty
egg-capsules, but in this they only act like many other much admired
Insects. _S. orientalis_ is gregarious, and the individuals are very
amicable with one another; small specimens sit on, or run over the big
individuals, and even nestle under them without their displaying the least
resentment. The common cockroach is a rather amusing pet, as the creatures
occasionally assume most comical attitudes, especially when cleaning their
limbs; this they do somewhat after the fashion of cats, extending the head
as far as they can in the desired direction, and then passing a leg or
antenna through the mouth; or they comb other parts of the body with the
spines on the legs, sometimes twisting and distorting themselves
considerably in order to reach some not very accessible part of the body.
There is very little information extant as to the domestic Blattidae found
in parts of the world outside Europe, but it seems that there are numerous
species that prefer the dwellings of man, even though they only tolerate
the owners. Belt says[159] "the cockroaches that infest the houses of the
tropics are very wary, as they have numerous enemies—birds, rats,
scorpions, and spiders; their long trembling antennae are ever stretched
out, vibrating as if feeling the very texture of the air around them; and
their long legs quickly take them out of danger. Sometimes {232}I tried to
chase one of them up to a corner where on a wall a large cockroach-eating
spider stood motionless looking out for his prey; the cockroach would rush
away from me in the greatest fear, but as soon as it came within a foot of
its mortal foe nothing would force it onwards, but back it would double,
facing all the danger from me rather than advance nearer to its natural
enemy." To this we may add that cockroaches are the natural prey of the
fossorial Hymenoptera of the group Ampulicides, and that these wasps
sometimes enter houses in search of the Insects.
[Illustration: FIG. 127.—_Nocticola simoni_. A, male; A_{1}, tegmen and
rudiment of wing; A_{2}, front of head; B, female. The cerci are broken, in
B the right one is restored in outline. (After Bolivar.)]
We have already noticed the considerable difference that exists in many
cases between the sexes of the same species. This is sometimes carried to
such an extent that nothing but direct observation could make us believe
that the males and females are of one kin. Fig. 118 (p. 220) shows a case
of this kind. Though the young as a rule are excessively similar to the
adults, yet this is by no means invariably the case. In some of the more
amply winged forms, such as _Blabera_, the young is about as different from
the adult as the female of _Heterogamia_ {233}is from its male. In
Blattidae it is always the case—so far as is yet known—that when there is a
difference as regards the alar organs between the two sexes, it is the male
that has these structures most developed, and this even when they can be of
little or no use for purposes of flight.
Among the most interesting forms of the family are the two species of the
genus _Nocticola_, recently discovered by M. Simon in caves in the
Philippine Islands.[160] They are amongst the smallest of the Orthoptera,
the male being scarcely ⅛ of an inch long. In the larval state of _N.
simoni_ the ocular organs exist as three ocelli, or facets, on each side of
the head, and in the perfect state the number is increased somewhat, as
shown in Fig. 127, A_{2}. In the second species of the genus the female is
quite blind (the male being still undiscovered). The fenestræ in
_Nocticola_ are absent; the tegmina and wings are totally wanting in the
female (Fig. 127, B), but are present in a very peculiar condition in the
male (Fig. 127, A_{1}). There are other anomalies in the structure of these
cavernicolous Insects, the cerci being apparently of peculiar structure,
and the spines of the legs more hair-like than usual. The condition of the
eyes is remarkable; the peculiarity in their development is worthy of
study.
[Illustration: FIG. 128.—_Corydia petiveriana_, with tegmina extended, A;
closed, B.]
To those who are acquainted with Blattidae only through our domestic "black
beetle" it may seem absurd to talk of elegance in connexion with
cockroaches. Yet there are numerous forms in which grace and beauty are
attained, and some exhibit peculiarities of ornamentation that are worthy
of attention. _Corydia petiveriana_ (Fig. 128) is a common cockroach in
East India. It has an effective system of coloration, the under wings and
the sides of the body being vividly coloured with orange yellow; when the
tegmina are closed the upper surface of the body is of a velvet-black
colour, with cream-coloured marks; these spots are different {234}on the
two tegmina, as shown in Fig. 128, A, but are so arranged that when the
tegmina are closed (Fig. 128, B) a symmetrical pattern is produced by the
combination of the marks of the two differently spotted tegmina. It is very
curious to notice the great difference in the colour of the part of the
right tegmen that is overlapped by the edge of the left one; this part of
the tegmen being coloured orange yellow in harmony with the wings. The
result of the remarkable differentiation of the colours of the two tegmina
may be summarised by saying that on the right one the colour of a part is
abruptly contrasted with that of the rest of the organ, so as to share the
system of coloration of the under-wings and body, while the corresponding
part of the other tegmen is very different, and completes the system of
symmetrical ornamentation of the upper surface.
Many other members of the Blattidae have an elegant appearance, and depart
more or less from their fellows in structural characters, with the result
of adding to their graceful appearance; in such cases, so far as at present
known, these Insects are brightly coloured. Thus _Hypnorna amoena_ (Fig.
129) has the antennae banded in white, black, and red, while the
overlapping part of the tegmina is arranged so as to bring the line of
junction between them nearly straight along the middle line of the body,
and thus produce a more symmetrical appearance than we find in other
cockroaches. The head in this Insect is not so concealed as usual, and this
undoubtedly adds somewhat to the effective appearance of this cockroach.
This visibility of the front of the head in _Hypnorna_ is not, as would be
supposed, owing to its being less inflexed than usual. On the contrary, the
head is quite as strongly inflexed as it is in other Blattidae, but the
part just at the front of the thorax is unusually elongate, so that the
eyes are exposed and the Insect has a larger field of vision. This
interesting Insect belongs to the tribe Oxyhaloides [Plectopterinae
Sauss.], in which group the most highly developed folded wings occur.
[Illustration: FIG. 129.—_Hypnorna amoena_. Central America. Tribe
Oxyhaloides. (After de Saussure.)]
The wingless forms never exhibit the grace and elegance possessed by some
of the more active of the winged Blattidae. {235}One of them,
_Gromphadorhina portentosa_, found in Madagascar (Fig. 130), is a very
robust Insect, and attains a length of 78 millim.—somewhat more than 3
inches. This Insect has projections on the thorax that remind us of the
horns that exist in some of the Lamellicorn beetles.