Chapter XIV: Introduction: Habits–classification–structure–chilognatha–chilopoda (8)

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.

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.

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.

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_.

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]

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.

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.

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.

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.

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.

Little has been yet written as to the resemblances of Blattidae to other species of their own family, or to other creatures, but it is probable that such similarities will be found to prevail to a considerable extent. W. A. Forbes has called attention[161] to the larva of a Blattid from Brazil as being remarkable for its superficial resemblance to an Isopod crustacean. Some of the wingless forms have a great resemblance to the small rolling-up Myriapods of the group Glomerides; _Pseudoglomeris fornicata_, of which we figure the female (Fig. 131), has received its name from this resemblance. The females of the S. African genus _Derocalymma_ possess this Glomerid appearance, and have a peculiar structure of the prothorax, admitting of a more complete protection of the head. Brunner states that the wingless kinds of _Derocalymma_ roll themselves up like wood-lice. In many of the forms of this tribe—Perisphaeriides—the males are winged, though the females are so like Myriapods. According to de Saussure[162] the gigantic _Megaloblatta rufipes_ bears an extreme resemblance in appearance to the large cockroaches of the genus _Blabera_.

Some of the species of _Holocompsa_ remind us strongly of Hemiptera of the family Capsidae; they have an arrangement of colours similar to what prevails in that group, and their tegmina and wings which, as being those of Blattids may be said to be abnormally formed, resemble in texture and the distribution of the venation those of the Hemiptera. These Insects are closely allied to _Diaphana_, of which genus we have figured a species (Fig. 122).

{236}There is very little evidence on which to base an estimate of the number of species of Blattidae existing in the world at present. Probably the number extant in collections may amount to 1000 or thereabouts, and the total existing in the world may be as many as 5000. The species of Blattidae cannot tolerate cold, and are consequently only numerous in tropical regions. Europe possesses about twenty species, and in Britain there are only three that are truly native; these are all small Insects belonging to the genus _Ectobia_, and living out of doors, amongst leaves, under bushes, and in various other places. We have, however, several other species that have been introduced by the agency of man, and these all live under cover, where there is artificial warmth and they are protected from the inclemencies of the winter season. The commonest of these forms is _Stilopyga orientalis_, the "black beetle" of our kitchens and bakehouses. This Insect is said to have been brought to Europe from "Asia" about 200 years ago, but the evidence as to its introduction, and as to the country of which it is really a native, is very slight. It is indeed said[163] that _S. orientalis_ has been found in peat in Schleswig-Holstein. _Periplaneta americana_ is a larger Insect, and is common in some places; it is apparently the species that is most usually found on board ships, where it sometimes multiplies enormously, and entirely devours stores of farinaceous food to which it obtains access: it is known that sometimes a box or barrel supposed to contain biscuits, on being opened is found to have its edible contents entirely replaced by a mass of living cockroaches. Fortunately _Periplaneta americana_ has not spread widely in this country, though it is found in great numbers in limited localities; one of the best known of which is the Zoological Gardens in the Regent's Park at London. _Periplaneta australasiae_ is very similar to _P. americana_, but has a yellow mark on the shoulder of each tegmen. This has obtained a footing in some of the glass-houses in the Botanic Gardens at Cambridge and Kew; and it is said to be fairly well established in Belfast. Another of our introduced domestic cockroaches is _Phyllodromia germanica_, a much smaller Insect than the others we have mentioned. It has only established itself at a few places in this country, but it is extremely abundant in some parts of Northern and Eastern Europe. It has been increasing in numbers in Vienna, where, according to Brunner, it is {237}displacing _Stilopyga orientalis_. In addition to these, _Rhyparobia maderae_ and species of the genus _Blabera_ have been met with in our docks, and are possibly always to be found there. They are Insects of much larger size than those we have mentioned. We figure the alar organs of one of these species of _Blabera_ of the natural size: the species in this genus are extremely similar to one another. Blaberae are known in the West Indies as drummers, it being supposed that they make a noise at night,[164] but details in confirmation of this statement are wanting.

It is a remarkable fact that no satisfactory reasons can be assigned for the prevalence of one rather than another of these domestic cockroaches in particular localities. It does not seem to depend at all on size, or on the period of development, for the three species _Stilopyga orientalis_, _Periplaneta americana_, and _Phyllodromia germanica_, which are the most abundant, differ much in these respects, and replace one another in particular localities, so that it does not appear that any one is gaining a permanent or widespread superiority as compared with another. There are, however, no sufficient records on these points, and further investigation may reveal facts of which we are at present ignorant, and which will throw some light on this subject. We may remark that Mr. Brindley has found it more difficult to obtain hatching of the young from the egg-capsules of _Periplaneta americana_ and _Phyllodromia germanica_ at Cambridge, than from those of _Stilopyga orientalis_.

Although much work has been done on the embryology of Blattidae, the subject is still very incomplete. The recent memoirs of Cholodkovsky[165] on _Phyllodromia germanica_ contain so much of general interest as to the development of the external parts of the body that we may briefly allude to them. The earliest appearance of segmentation appears to be due to the centralisation of numerous {238}cells round certain points in the ventral plate. The segmentation of the anterior parts is first distinct, and the appearance of the appendages of the body takes place in regular order from before backwards, the antennae appearing first; the mandibles, however, become distinct only subsequent to the maxillae and thoracic appendages. There are in the course of the development appendages to each segment of the body (he counts eleven abdominal segments); the cerci develop in a similar manner to the antennae; the first pair of abdominal appendages—at first similar to the others—afterwards assume a peculiar stalked form. The abdominal appendages subsequently disappear, with the exception of the ninth pair, which form the ventral styles, and the eleventh pair, which become the cerci. The last ventral segment is said to be formed by the union of the tenth and eleventh embryonic ventral segments.

As regards their Palaeontological forms Blattidae are amongst the most interesting of Insects, for it is certain that in the Carboniferous epoch they existed in considerable number and variety. A still earlier fossil has been found in the Silurian sandstone of Calvados; it consists of a fragment (Fig. 133, A), looking somewhat like an imperfect tegmen of a Blattid; it was described by Brongniart under the name of _Palaeoblattina douvillei_, and referred by him, with some doubt, to this family. Brauer has, however, expressed the opinion[166] that the fragment more probably belonged to an Insect like the mole-cricket, and in view of this discrepancy of authorities we may be pardoned for expressing our own opinion to the effect that the relic has no connexion with the Insecta. The figure given by Scudder[167] has not, however, so uninsect-like an appearance as that we have copied from Brauer. Whatever may prove to be the case with regard to _Palaeoblattina_, it is certain, as we {239}have already said, that in the Palaeozoic epoch Insects similar to our existing cockroaches were abundant, their remains being found in plenty in the coal-measures both of Europe and North America. Fig. 133, B, shows a fossil tegmen of _Etoblattina manebachensis_ from the upper Carboniferous beds of Ilmenau in Germany. It will be noticed that the disposition of the nervures is very much like that which may be seen in some of our existing Blattidae (cf. the tegmen of _Blabera_, Fig. 132, A), the vena dividens (_a_) being similarly placed, as is also the mediastinal vein on the front part of the organ. The numerous carboniferous Blattidae have been separated as a distinct Order of Insects by Scudder under the name Palaeoblattariae, but apparently rather on theoretical grounds than because of any ascertained important structural distinctions. He also divided the Palaeoblattariae into two groups, Mylacridae and Blattinariae, the former of which was supposed to be peculiar to America. Brongniart has, however, recently discovered that in the Carboniferous deposits of Commentry in France Mylacridae are as common as in America. This latter authority also states that some of the females of these fossil Blattidae are distinguished by the presence of an elongate exserted organ at the end of the body. He considers this to have been an ovipositor by which the eggs were deposited in trees or other receptacles, after a manner that is common in certain Orthoptera at the present day. If this view be correct these Carboniferous Insects must have been very different from the Blattidae of our own epoch, one of whose marked characteristics is the deposition of the eggs in a capsule formed in the body of the parent.

In the strata of the secondary epoch remains of Blattidae have also been discovered in both Europe and America, in Oolitic, Liassic, and Triassic deposits. From the Tertiary strata, on the other hand, comparatively few species have been brought to light. A few have been discovered preserved in amber.

The classification of the Blattidae is attended with considerable difficulty on account of the numerous wingless forms, and of the {240}extreme difference in the organisation of the two sexes of many species. It has, however, been brought to a fairly satisfactory state by the reiterated labours of Brunner von Wattenwyl, and we reproduce his recently perfected exposition of their characters. His first division is made by means of a structure which is very easily observed, viz. whether the femora are armed with spines, as in Fig. 134, or not. The terms used in connexion with the wings and other parts of the body we have already explained.

Brunner's system is adopted by de Saussure,[168] who, however, proposes to replace the names Ectobiides and Oxyhaloides by Anaplectinae and Plectopterinae. He also proposes to apply the generic name _Blatta_ to the Insect that is now so frequently called _Phyllodromia germanica_ in zoological works. If that view be adopted, Brunner's group Phyllodromiides will be called Blattides.

Table of the tribes of Blattidae, after Brunner:—

1. Femora spiny beneath.[169]

2. The last ventral plate of the female large, without valves.

3. Supra-anal lamina of both male and female transverse, narrow.
Wings, when present, furnished with a triangular apical field.
Posterior femora unarmed beneath, or armed with two spines on the
anterior margin. Egg-capsules furnished with a longitudinal suture.
Tribe 1. ECTOBIIDES. [Anaplectinae Saussure.]

3′. Supra-anal lamina of each sex more or less produced, triangular,
or emarginate. Wings, when present, without apical field. Posterior
femora with both edges spiny.

4. Supra-anal lamina of each sex triangular, not notched. Cerci
projecting much beyond this lamina.

5. Pronotum and elytra smooth (_i.e._ without peculiarity of
surface other than punctuation). The radial nervure of the wing
giving off several parallel branches, pectinate on the anterior
margin (except in the genus _Abrodiaeta_). Tarsal joints without
pads. Tribe 2. PHYLLODROMIIDES. [Blattinae Saussure.]

5′. Pronotum and elytra holosericeous. Radial nervure of the
wings giving off irregular branches on the anterior margin (ulnar
vein many-branched). Tarsal joints furnished with pads. Tribe 3.
NYCTIBORIDES.

4′. Supra-anal lamina of males more or less four-sided, with obtuse
angles, of females broad, rounded, or lobed. Cerci not projecting
beyond the lamina. (Tarsal joints with distinct pads.) Ulnar
nervure of the wings giving off parallel branches towards the vena
dividens. Tribe 4. EPILAMPRIDES.

{241}2′. The last ventral plate of the female furnished with valves.
Tribe 5. PERIPLANETIDES.[170] (Fig. 119, _Periplaneta australasiae_.)

1′. Femora unarmed beneath. (In the tribe Panesthiides the anterior
femora are frequently armed with two spines.)

2. Supra-anal lamina of each sex more or less produced, posterior
margin notched.

3. A distinct pad between the claws. Tribe 6. PANCHLORIDES.

3′. No pad between the claws, or only an excessively small one.

4. Wings with a folded fan-like anal field. Pronotum smooth. Tribe
7. BLABERIDES. (Fig. 132, _Blabera_ sp. wings.)

4′. Anal field of the wing with a single fold. Pronotum more or
less pilose. Tribe 8. CORYDIIDES. (Fig. 128, _Corydia petiveriana_.
Fig. 118, _Heterogamia aegyptiaca_.)

2′. Supra-anal lamina of each sex, short, transverse, posterior margin
straight or rounded.

3. Subgenital lamina of the male somewhat produced, furnished with a
single style. Tarsal claws with a distinct pad (except in the genus
_Paranauphoeta_).

4. Anterior portion of the wings pointed, either the apical field
of the wing very much produced, or the wings twice as long as the
tegmina, folded in repose. Tribe 9. OXYHALOIDES. [Plectopterinae
Saussure.] (Fig. 129, _Hypnorna amoena_.)

4′. Anterior portion of wing, when present, rounded, with no apical
field. Tribe 10. PERISPHAERIIDES. (Fig. 130, _Gromphadorhina
portentosa_; Fig. 131, _Pseudoglomeris fornicata_.)

3′. Subgenital lamina of males extremely small, without styles. No
pad between claws. Tribe 11. PANESTHIIDES.

To the above tribes another one—GEOSCAPHEUSIDES—has been recently added by Tepper,[171] for an extraordinary Australian Insect of fossorial habits, with front legs formed somewhat like those of _Gryllotalpa_.

{242}CHAPTER X

ORTHOPTERA _CONTINUED_—MANTIDAE—SOOTHSAYERS

FAM. IV. MANTIDAE—SOOTHSAYERS OR PRAYING INSECTS.

_Orthoptera with exserted but deflexed head and elongate prothorax, the
first pair of legs largely developed, raptorial, the coxae elongate,
free, femora and tibiae armed with spines: second and third pair of legs
simple and similar; the tarsi five-jointed, without a pad (arolium)
between the claws; a pair of jointed cerci near the extremity of the
body._

The Mantidae are an extensive family of Orthoptera, showing extreme variety in the shapes and outlines of the body, and characterised by the very remarkable front legs; the function of these legs being to seize and hold their prey, which consists of living Insects, Mantidae being carnivorous and highly voracious.

The labium is deeply divided, each half exhibiting a very near approach to the structure of a maxilla; there is a large membranous lingua reposing on the inner face of the lower lip. The head is quite free from the thorax, its front part being deflexed, and even somewhat inflexed, so that the mouth is directed downwards and somewhat backwards: it is very mobile, being connected to the thorax by a comparatively slender neck, which is, however, concealed by the pronotum. There are two large, prominent eyes, the antennae are frequently very slender, but they sometimes differ according to sex, and in some genera are pectinate in the male; just above and between their insertion are three ocelli placed in a triangle, two above, one below; between the antennae and the clypeus there is an interval called the scutellar space. In some forms of Mantidae the head assumes most extraordinary shapes; the eyes may become {243}elongate and horn-like; there may be a projection between them bearing the ocelli, and attaining occasionally a great length; the scutellar space also may have a remarkable development, the whole thus forming a peculiar ornamental structure, as in Fig. 136.

The prothorax is elongate, but there are a few genera, _e.g._ _Eremiaphila_, in which it is exceptionally short, and there are several others in which the elongate form is more or less masked by foliaceous expansions of the sides. The pronotum shows near the front a transverse depression or seam, which marks the position of an internal chitinous ridge. The anterior legs are {244}inserted near the front of the prosternum, which extends less far forwards than the pronotum does; the posterior part of the prosternum is very elongate, and is completely separated from the anterior part by the base of the coxae and the membranes attached to them; the pronotum and sternum are closely connected at the sides till near the posterior part where they diverge, the space so formed being occupied by a membrane in which the prothoracic stigma is situated. The mesothorax is as long as broad, and the front wings are attached to the whole length of the sides; the mesosternum is a triangular piece pointed behind, and bearing very large side-pieces, to the hinder portion of which the middle coxae are attached; these latter are large and quite free, and repose on the metasternum which they cover; the mesothoracic stigma may be detected as a slit situated on a slight prominence just behind and a little below the membranous hind-margin of the tegmen. The metathorax differs comparatively little in size and structure from the mesothorax; the membranous hind wings are attached to the sides of the notum along nearly the whole length of the latter. The abdomen is moderately long; in each sex ten dorsal plates may be detected, and there is a pair of ringed cerci projecting from beneath the sides of the tenth plate. The number of ventral plates is more difficult to verify, the first one being much reduced; eight other plates can be demonstrated in the male and six in the female.

The anterior legs are formed in a remarkable manner in the Mantidae, and are, in fact, the most characteristic feature of the family. Attached near the front of the thorax there is a very long coxa, to the apex of which is articulated the triangular trochanter; this bears the elongate femur, which is furnished on its lower face with sharp spines and teeth; the tibia which follows is much shorter and smaller than the femur; its lower face bears also an armature of teeth, and it is so articulated with {245}the femur that it can be completely closed thereon, its teeth fitting in among those of the femur (Fig. 137, B); the latter has one or more longer spines overlapping the apical part of the tibia when contracted. The tarsus is slender, five-jointed, without pad. The other two pairs of legs are simple; the hinder usually a little the longer, and in some species that possess powers of leaping (_Ameles_), with the femora a little thicker at the base.

The alar organs of the Mantidae are as regards the nervures and areas fairly similar to those of the Blattidae. The tegmina are usually narrow, and exhibit three well-marked areas; the one in front or external (according as the wing is expanded or closed) is the mediastinal area; it is usually more elongate and occupies a larger portion of the surface of the tegmen than in Blattidae. The middle area, forming the larger part of the wing, is occupied by the branches of the radial and ulnar nervures. The third area, the anal, possesses a sort of appendage in the form of a small space of a more delicately membranous nature at the inner part of the base. The tegmina are often more or less leaf-like in texture and consistence; this character is as a rule not very marked, but there are a few species with the tegmina very like foliage, this being more marked in the female; in some, if not in all, of these cases the mediastinal area is considerably increased. One tegmen overlaps the other, as in Blattidae, but to a less extent, and the correlative asymmetry is but slight: there is frequently a pallid spot close to the main vein on the principal area, nearer to the base than to the extremity. The hind wings are more ample than the front, and of much more delicate consistence; they possess numerous veins converging to the base; the anterior part of the wing is firmer in consistence, and its veins are more numerously furcate; there are many more or less distinct minute cross-veinlets, and an elegant tinting is not infrequent. They close in a fan-like manner, transverse folding being unknown in the family.

{246}But little has been written on the internal anatomy of the Mantidae. Dufour has described only very partially that of _M. religiosa_. The salivary glands are largely developed, salivary receptacles exist; the alimentary canal possesses eight elongate coecal diverticula placed on the chylific ventricle; there are about one hundred Malphigian tubules. In each ovary there are about 40 egg-tubes, and they are joined at their bases in clusters of about half a dozen; each cluster has a common sinus; these sinuses are placed at intervals along a tube, which is one of two branches whose union forms the oviduct; there are a large number of "serific glands" of two kinds in the female. The testes are unusually complex in their structure.

According to Schindler[172] the Malphigian tubes in _Mantis_ are not inserted, as usual, at the base of the intestine, but on the intestine itself at about one-third of its length from the base. There is some doubt about this observation. Schindler considers the fact, if it be such, unique.

The eggs of the Mantidae are deposited in a singular manner: the female, placing the extremity of the body against a twig or stone, emits some foam-like matter in which the eggs are contained. This substance dries and forms the ootheca; whilst attaining a sufficient consistence it is maintained in position by the extremity of the body and the tips of the elytra, and it is shaped and fashioned by these parts. The eggs are not, as might be supposed, distributed at random through the case, but are lodged in symmetrically-arranged chambers, though how these chambers come into existence by the aid of so simple a mode of construction does not appear. The capsule is hard; it quite conceals the eggs, which might very naturally be supposed to be efficiently protected by their covering: this does not, however, appear to be the case, as it is recorded that they are subject to the attacks of Hymenopterous parasites. The time that elapses after the eggs are laid and before they hatch varies greatly according to circumstances. In France, _Mantis religiosa_ deposits its eggs in September, but they do not hatch until the following June; while in E. India the young of another species of _Mantis_ emerge from the eggs about twenty days after these have been deposited. Trimen has recorded some particulars as to the formation of its egg-case by a _Mantis_ in S. Africa. This {247}specimen constructed four nests of eggs at intervals of about a fortnight, and Trimen states that the four were "as nearly as possible of the same size and of precisely similar shape." He also describes its mode of feeding, and says that it was fond of house-flies, and would eat "blue-bottles," i.e. _Musca vomitoria_, but if while eating one of the latter a house-fly were introduced, the "blue-bottle" was generally dropped, even though it might be in process of being devoured. The young have to escape from the chambers in which they are confined in these egg-cases; they do so in a most curious manner; not by the use of the feet, but by means of spines directed backwards on the cerci and legs, so that when the body is agitated advance is made in only one direction. The eggs last deposited are said to be the first to hatch. On reaching the exterior the young Mantids do not fall to the ground, but remain suspended, after the manner of spiders, to the ootheca by means of two threads attached to the extremities of the cerci; in this strange position they remain for some days until the first change of skin is effected, after which they commence the activity of their predatory life.

Dr. Pagenstecher has given an account[173] of the development of _Mantis religiosa_, from which it would appear that the statements of Fischer and others as to the number of moults are erroneous, owing to the earliest stages not having been observed. When the young _Mantis_ emerges from the egg it bears little resemblance to the future Insect, but looks more like a tiny pupa; the front legs, that will afterwards become so remarkable, are short and not different from the others, and the head is in a curious mummy-like state, with the mouth-parts undeveloped and is inflexed on the breast: there are, he says, nine abdominal segments. The first ecdysis soon takes place and the creature is thereafter recognisable as a young _Mantis_. Pagenstecher's specimens at first would only eat Aphididae, but at a later stage of the {248}development they devoured other Insects greedily: the number of ecdyses is seven or eight. The ocelli appear for the first time when the wing rudiments do so; the number of joints in the antennae increases at each moult. Dr. Pagenstecher considers that this Insect undergoes its chief metamorphosis immediately after leaving the egg, the earlier condition existing apparently to fit the Insect for escaping from the egg-case. In the immature stage of the Mantidae the alar organs appear (Fig. 139) as adjuncts of the sides of the meso- and meta-notum, projecting backwards and very deeply furrowed and ribbed in a wing-like manner. According to Pagenstecher, this wing-like appearance only commences in the fifth stadium, but he has not given particulars of the conditions of these parts in the preceding instars. According to de Saussure[174] the wings of the females of some species remain permanently in this undeveloped or nymphal state.