Chapter VII: Introduction: Habits–classification–structure–chilognatha–chilopoda (1)

SCHIZOTARSIA–SYMPHYLA–PAUROPODA–EMBRYOLOGY–PALAEONTOLOGY.

_Tracheata_ with separated head and numerous, fairly similar segments. They have one pair of antennae, two or three pairs of mouth appendages, and numerous pairs of legs.

The Myriapoda are a class of animals which are widely distributed, and are represented in almost every part of the globe. Heat and cold alike seem to offer favourable conditions for their existence, and they flourish both in the most fertile and the most barren countries.

They have not attracted much notice until comparatively recent times. Compared with Insects they have been but little known. The reason of this is not hard to find. The Myriapods do not exercise so much direct influence on human affairs as do some other classes of animals; for instance, Insects. They include no species which is of direct use to man, like the silkworm or the cochineal insect, and they are of no use to him as food. It is true that they are injurious to his crops. For instance, the species of Millepede known as the "wire worm"[10] is extremely harmful; but this has only attracted much notice in modern times, when land is of more value than formerly, and agriculture is pursued in a more scientific manner, and the constant endeavour to get the utmost amount of crop from the soil has caused a minute investigation into the various species of animals which are noxious to the growing crop. The species of {30}Myriapoda best known to the ancients were those which were harmful to man on account of their poisonous bite.

Some writers have supposed that the word which is translated "mole" in the Bible (Lev. xi. 30) is really _Scolopendra_ (a genus of Centipede), and, if this is so, it is the earliest mention of the Myriapods. They were rarely noticed in the classical times; almost the only mention of them is by Ælian, who says that the whole population of a town called Rhetium were driven out by a swarm of Scolopendras. Pliny tells us of a marine Scolopendra, but this was most probably a species of marine worm.

Linnaeus included Myriapods among the Insects; and the writers after him till the beginning of this century classed them with all sorts of Insects, with Spiders, Scorpions, and even among Serpents. It was Leach who first raised them to the importance of a separate class, and Latreille first gave them the name of Myriapoda, which they have retained ever since.

Myriapods are terrestrial animals, crawling or creeping on the ground or on logs of wood, or even under the bark of trees. There is, however, a partial exception to this; various naturalists have from time to time given descriptions of marine Centipedes. These are not found in the sea, but crawl about on the shore, where they are submerged by each tide. Professor F. Plateau has given an account of the two species of Myriapods that are found thus living a semi-aquatic life. They are named _Geophilus maritimus_ and _Geophilus submarinus_, and Plateau found that they could exist in sea water from twelve to seventy hours, and in fresh water from six to ten days. They thus offer a striking example of the power that their class possess of existing under unfavourable circumstances.

With regard to their habits the different species differ very considerably. On the one hand we have the Chilopoda, or Centipedes, as they are called in this country, active, swift, and ferocious; living for the most part in dark and obscure places, beneath stones, logs of wood, and dried leaves, etc., and feeding on living animals. On the other hand, we have the Chilognatha, or Millepedes, distinguished by their slow movements and vegetable diet; inoffensive to man, except by the destruction they occasion to his crops, and having as a means of defence no formidable weapon like the large poison claws of the Centipedes, but only a peculiarly offensive liquid secreted by special glands {31}known by the unpleasant though expressive name of "stink glands," or by the more euphonious Latin name of _glandulae odoriferae_.

As a general rule the larger species of Myriapods are found in the hotter climates, some of the tropical species being very large, and some, among the family of the Scolopendridae, extremely poisonous; and it is even said that their bite is fatal to man.

If, however, the Centipede is sometimes fatal to man, it does not always have it its own way, for we read of man making food of Centipedes. It is hard to believe that any human being could under any circumstances eat Centipedes, which have been described by one naturalist as "a disgusting tribe loving the darkness." Nevertheless, Humboldt informs us that he has seen the Indian children drag out of the earth Centipedes eighteen inches long and more than half an inch wide and devour them.

This, I believe, is the only account of human beings using the Myriapoda as food, if we except the accounts of the religious fanatics among the African Arabs, who are said to devour Centipedes alive; though this is not a case of eating for pleasure, for the Scolopendras are devoured in company with leaves of the prickly pear, broken glass, etc., as a test of the unpleasant things which may be eaten under the influence of religious excitement.

{32}A cold climate, however, is not fatal to some fairly large species of Centipedes. A striking instance of this came under my own observation some years ago. In 1886 I was travelling in the island of Cyprus—the "Enchanted Island," as Mr. Mallock calls it in his book written about the same time—with the intention of observing its natural history. This island consists of a broad flat country crossed by two mountain ranges of considerable height, thus offering the contrast of a hot climate in the plains and a cold climate in the mountains. On the plain country I found among the Myriapoda that the most common species were a large _Scolopendra_ and a large _Lithobius_. The _Scolopendra_ was fairly common, living for the most part under large stones, and it was a pleasant task to search for them in a ruined garden near Larnaca.

This garden was made for the public, and is situated about a quarter of a mile from the old town of Larnaca. It has been suffered to fall into decay, and is now quite neglected. Mr. Mallock has described many beautiful scenes in his book, but I think he could have found few more beautiful than this old garden with its deserted gardener's house, now a heap of ruins, but overgrown with masses of luxuriant vegetation, with beautiful flowers peeping out here and there as if charitably endeavouring to hide the negligence of man, and to turn the desolation into a scene of beauty. I got several prizes in this garden, but found the Myriapods were principally represented by the species I have mentioned.

After leaving Larnaca I rode across the plain country through blazing heat, which was rapidly parching up the ground to a uniform brown colour. At every stopping-place I found the same species of _Scolopendra_ and of _Lithobius_. After a few days I began to get up among the mountains of the northern range, and the burning heat of the treeless plain was gradually exchanged for the cool shade of the pine-trees and the fresh air of the mountains. As I ascended higher and higher the temperature grew cooler till I reached the top of Mount Troodos, the ancient Olympus. Here in the month of May the snow still lingered in white patches, and the air was clear and cold. I remained on the top of Troodos for a week, while I made a close examination of the fauna to be found there. I was much surprised to find the identical species of _Scolopendra_ and {33}_Lithobius_ with which I had become acquainted in the heat of the low country, quite at home among the snow, and as common as in, what I should have imagined to be, the more congenial climate. Nor were they any the less lively. Far from exhibiting any sort of torpor from the cold, the first one which I triumphantly seized in my forceps wriggled himself loose and fastened on my finger with a vigour which made me as anxious to get rid of him as I had formerly been to secure him. However, he eventually went into my collecting box.

On the whole, we may say that the Chilopoda are most largely represented in the hotter climates, where they find a more abundant diet in the rich insect life of the tropical and semi-tropical countries. The more brightly-coloured Myriapods, too, are for the most part inhabitants of the warmer countries. The ease with which they are introduced into a country in the earth round plants, and in boxes of fruit, may account to a great extent for the wide distribution of the various species in different countries. Mr. Pocock, who examined the Myriapods brought back from the "Challenger" Expedition, informs us that of ten species brought from Bermuda, four had been introduced from the West Indies. There is no doubt that animals which can bear changes of temperature and deprivation of food, and even a short immersion in the water, are well calculated to be introduced into strange countries in many unexpected ways.

As might be expected from a class of animals so widely distributed, Myriapods show an almost infinite variety of size and colour. We find them so small that we can hardly see them with the naked eye, as in the case of the tiny _Polyxenus_, the Pauropidae, and the Scolopendrellidae. We also find them more than six inches in length, as the larger species of Scolopendridae. I am afraid we must dismiss as an exaggeration an account of Centipedes in Carthagena a yard in length, and more than six inches in breadth. The giver of this account—Ulloa—informs us that the bite of this gigantic serpent-like creature is mortal if a timely remedy be not applied. It is certainly extremely probable that the bite of a Centipede of this size would be fatal to any one. Some Centipedes are short and broad, and composed of few segments, as _Glomeris_; some are long and thin, with more than a hundred segments, as _Geophilus_. They may be beautifully coloured with brilliant streaks of colour, as in some {34}of the Julidae or Polydesmidae, or may be of a dull and rusty iron colour, or quite black.

One of the strangest peculiarities found among Myriapods is that some of them (e.g. _Geophilus electricus_) are phosphorescent. As I was walking one summer evening near my home in Cambridgeshire I saw what I thought was a match burning. Looking more closely, I saw it move, and thinking it was a glow-worm I picked it up, and was surprised to find that it was a _Geophilus_ shining with a brilliant phosphorescent light. I let it crawl over my hand, and it left a bright trail of light behind it, which lasted some time. I have been told that this species is common in Epping Forest; also in Cambridgeshire.[11]

Besides _G. electricus_, _G. phosphoreus_ has been described as a luminous species by Linnaeus, on the authority of a Swedish sea captain, who asserted that it dropped from the air, shining like a glow-worm, upon his ship when he was sailing in the Indian Ocean a hundred miles from land.

What the use of this phosphorescence may be is not known with any degree of certainty. It may be either a defence against enemies, or else a means of attracting the two sexes to one another.

The places which the Myriapods select for their habitation vary as much as their colour and size, though, with a few exceptions, they chose dark and obscure places. A curious species of Myriapod is _Pseudotremia cavernarum_ (Cope), which is found in certain caves in America. The peculiar life it leads in these caves seems to have a great influence on its colour, and also affects the development of its eyes. Mr. Packard's account of them is worth quoting: "Four specimens which I collected in Little Wyandotte cave were exactly the same size as those from Great Wyandotte cave. They were white tinged, dusky on the head and fore part of the body. The eyes are black and the eye-patch of the same size and shape, while the antennae are the same.

"Six specimens from Bradford cave, Ind. (which is a small grotto formed by a vertical fissure in the rock, and only 300 to 400 yards deep), showed more variation than those from the two Wyandotte caves. They are of the same size and form, but slightly longer and a little slenderer.... The antennae are much whiter than in those from the Wyandotte caves, and the {35}head and body are paler, more bleached out than most of the Wyandotte specimens.... It thus appears that the body is most bleached and the eyes the most rudimentary in the Bradford cave, the smallest and most accessible, and in which consequently there is the most variation in surroundings, temperature, access of light and changed condition of air. Under such circumstances as these we should naturally expect the most variation."[12]

A strong contrast to these animals is afforded us by the Scutigeridae (Schizotarsia). They are unknown in this country, but abound in some of the Mediterranean countries and in parts of Africa. They remind one strongly of spiders, with their long legs and their peculiar way of running on stones and about the walls of houses.

Some years ago I was in Malta, and I used to go and watch them on the slopes outside Valetta, where they were to be found in great numbers. They used to come out from beneath great stones and run about rapidly on the ground or on the stones and rubbish with which the ground was covered, now and again making a dart at some small insect which tempted them, and seemingly not minding the blazing sun at all. As might be expected from their habits, their eyes, far from being rudimentary, like those of the cave-living _Pseudotremia_, or absent {36}like those of the Polydesmidae, or of our own _Cryptops_, are highly developed, and form the only example among the Myriapods of what are known as facetted eyes. The Scutigeridae are also remarkable among Myriapods for the possession of a peculiar sense-organ which is found in no other Myriapod.

The Myriapods most numerous in our own country are _Lithobius_ and _Julus_. _Lithobius_, which will be described later on, may be found in almost any garden under dried leaves, stones, etc. _Julus_, the common wire-worm, is found crawling on plants and leaves and under the bark of trees, and does a good deal of damage in a garden. _Polydesmus_ is also frequently found in great numbers, and usually a great many of them together. _Glomeris_ is also found, though it is not so common as the first two mentioned animals. _Geophilus_ is also common, and especially in the south of England. Scolopendridae are only represented by a single genus, _Cryptops_, which is not very common, though by no means rare. The best place to find them is in manure heaps. The animals of this species are small compared to most Scolopendras, and have the peculiarity of being without any eyes.

_Scutigera_ is unrepresented in this country. One was found in Scotland some years ago by Mr. Gibson Carmichael, but was shown to have been imported, and not bred in the place.

The means of defence possessed by these animals also differ very much in the different species of Myriapods. In the Centipedes the animals are provided with a powerful weapon in the great poison claws which lie just beneath the mouth, and which are provided with large poison glands, which supply a fluid which runs through a canal in the hard substance of the claw and passes into the wound made by the latter. The effect of this fluid is instantaneous on the small animals which form the food of the Centipedes. I have myself watched _Lithobius_ in this country creep up to a blue-bottle fly and seize it between the poison claws. One powerful nip and the blue-bottle was dead, as if struck by lightning. I have also seen them kill worms and also other _Lithobius_ in the same way. When another _Lithobius_ is wounded by the poison claws it seems to be paralysed behind the wound. The Millepedes, on the other hand, have no such offensive and defensive weapon. They rely for protection on the fluid secreted by the _stigmata repugnatoria_ (or _glandulae odoriferae_) mentioned before. This fluid has been shown to contain prussic acid, and has a very unpleasant odour.

{37}

Most of the Millepedes are provided with these glands; but in the cave Myriapods mentioned before, the animals have not to contend against so many adversaries, and these glands almost disappear. Other Myriapods defend themselves by means of the long and stiff bristles with which they are provided, _e.g._ the little _Polyxenus_. This means of defence seems to have been more common among the fossil Myriapods than among those still living. Variations in the shape and size of the limbs are numerous, as might be expected in so large a class of animals. One of the most curious of such variations is found in a Centipede of the Scolopendra tribe, called _Eucorybas_, in which the last limbs are flattened out and provided with paddle-shaped lobes. The use of these is unknown, but it is probable that they are concerned in some way with the breeding habits of the animal. The habits of the Myriapods connected with their breeding are most interesting, but have been very insufficiently investigated. There is no doubt that a full inquiry into all such habits would be of great interest, and would help to answer some of the problems which are still unsolved in these forms. My own observations refer to two forms—_Julus terrestris_ among the Millepedes, and _Lithobius forficatus_ among the Centipedes. _Julus terrestris_ is one of the most common of the English Millepedes, and can be easily obtained. I kept them in large shallow glass vessels with a layer of earth at the bottom, and thus was able easily to watch the whole process. They breed in the months of May, June, and July. The female _Julus_ when about to lay her eggs sets to work to form a kind of nest or receptacle for her eggs. She burrows down into the earth, and at some distance below the surface begins the work. She moistens small bits of earth with the sticky fluid secreted by her salivary glands, which become extraordinarily active in the spring. She works up these bits of earth with her jaws and front legs till they are of a convenient size and shape, and places them together. When complete, the nest is shaped like a hollow sphere, the inside being smooth and even, while the outside is rough and shows the shape of the small knobs of earth of which it is composed. {38}She leaves a small opening in the top. The size of the whole nest is about that of a small nut. When she is ready to lay her eggs she passes them through the hole in the top, and usually lays about 60 to 100 eggs at a time. The eggs, which are very small, are coated with a glutinous fluid which causes them to adhere together. When they are all laid she closes up the aperture with a piece of earth moistened with her saliva; and having thus hermetically sealed the nest, she leaves the whole to its fate. The eggs hatch in about twelve days.

A naturalist named Verloef has lately found that the males of some Julidae undergo certain changes in the form of the legs and other organs in autumn and spring. These changes are probably connected with the breeding of the animal, and remind us of the changes undergone during the breeding season by salmon among the fishes.

_Julus_ breed very readily if carefully attended to and well supplied with food. If they cannot obtain the food they like they will not breed so well. I found that sliced apples with leaves and grass formed the best food for them.

The process in the case of _Lithobius_ is much harder to watch. _Lithobius_ is not so plentiful as _Julus terrestris_, and the animals are more impatient of captivity, more shy in their habits, and do not breed so readily.

In January 1889 I was given the use of a room in the New Museums at Cambridge, and was allowed to fit it up as I liked, so that I was able to try the effect of different degrees of light and darkness, and of different degrees of warmth. I succeeded in observing the whole process. The female _Lithobius_ is furnished with two small movable hooks at the end of the under surface of the body close to the opening of the oviduct. These small hooks have been observed by many naturalists, but their use has, so far as I know, never been described before. They play an important part in the proceedings following the laying of the egg. The time of breeding in _Lithobius_ is rather later than in _Julus_, and begins about June and continues till August. There are first of all some convulsive movements of the last segments of the body, and then in about ten minutes the egg appears at the entrance of the oviduct. The egg is a small sphere (about the size of a number five shot), rather larger than that of _Julus_, and is covered with a sticky slime {39}secreted by the large glands inside the body, usually called the accessory glands. When the egg falls out it is received by the little hooks, and is firmly clasped by them. This is the critical moment in the existence of the _Lithobius_ into which the egg is destined to develop. If a male _Lithobius_ sees the egg he makes a rush at the female, seizes the egg, and at once devours it. All the subsequent proceedings of the female seem to be directed to the frustration of this act of cannibalism. As soon as the egg is firmly clasped in the little hooks she rushes off to a convenient place away from the male, and uses her hooks to roll the egg round and round until it is completely covered by earth, which sticks to it owing to the viscous material with which it is coated; she also employs her hind legs, which have glands on the thighs, to effect her purpose. When the operation is complete the egg resembles a small round ball of mud, and is indistinguishable from the surrounding soil. It is thus safe from the voracious appetite of the male, and she leaves it to its fate. The number of eggs laid is small when compared with the number laid by _Julus_.

The food in the case of _Lithobius_ consisted of worms and blue-bottles, which were put alive into the glass vessel containing the _Lithobius_. I tried raw meat chopped up, but they did not thrive on it in the same way that they did on the living animals. I also put into their vessel bits of rotten wood containing larvae of insects, etc.

I have succeeded in bringing back some specimens of _Polydesmus_ alive from Madeira, and in getting them to breed in this country—of course in artificial warmth—and their way of laying eggs and making a nest resembles that of _Julus_. _Geophilus_ has one curious habit in connexion with the fertilisation of the female. The male spins a web and deposits in the middle of it a single spermatophore, and the female comes to the web to be fertilised. The Scolopendridae are said to bring forth their young alive, but I think the evidence for this is unsatisfactory. What have been taken for the young Scolopendrae are perhaps the large spermatophores of the male, which are not unlike a larval Myriapod in size and shape. I have never been able to observe the process of breeding in this family. I have had the spermatophores sent me from Gibraltar as "eggs," but a little examination soon showed me their real character.

{40}The mode of progression in the Myriapods differs considerably, as might be expected in a class in which the number of legs varies to such an extent. The swiftest among them are the Scutigeridae with their long spider-like legs. The Scolopendridae are also able to move with considerable rapidity, and are also able to move tail forward almost as well as in the ordinary manner. Where there are such a number of legs it becomes a curious question as to the order in which the animal moves them; and though several people have endeavoured to find this out, the number of legs to be moved and the rapid movements have rendered accurate observation impossible.

Some years ago Professor E. Ray Lankester tried to study the order in which the legs of Centipedes moved, and came to the conclusion (recorded in an amusing letter in _Nature_, 23rd May 1889) that if the animal had to study the question itself, it would not get on at all. He finishes his letter with the following verses:—

A Centipede was happy quite
Until a toad in fun
Said, "Pray which leg moves after which?"
This raised her doubts to such a pitch,
She fell exhausted in the ditch,
Not knowing how to run.

The progression of Millepedes is much slower than that of the Centipedes, and it is remarkable that when the animal is in motion a sort of wave runs down the long fringe-like row of feet. I have endeavoured to make out this motion, but have never been able to understand it satisfactorily. My belief was that the feet were moved in sets of five.

This wave-like peculiarity of motion is described in a curious old book, _An Essay towards a Natural History of Serpents_. Charles Owen, D.D. London, 1742: "The Ambua, so the natives of Brazil call the Millepedes and the Centipedes, are serpents. Those reptiles of thousand legs bend as they crawl along, and are reckoned very poisonous. In these Multipedes the mechanism of the body is very curious; in their going it is observable that on each side of their bodies every leg has its motion, one regularly after another, so that their legs, being numerous, form a kind of undulation, and thereby communicate to the body a swifter progression than one could imagine where {41}so many short feet are to take so many short steps, that follow one another rolling on like the waves of the sea."

Before proceeding to the classification of Myriapods, which will form the next part of this account, a few words on the common names for them may not be without interest.

In English we have the names Centipede and Millepede, and the Continental nations have similar names implying the possession of a hundred or a thousand legs, as the German "Tausendfüsse" and the French "Millepieds." Of course these are general words, simply implying the possession of a great number of legs. But we have also among the peasantry a name for Centipedes which conveys a much more accurate idea of the number. The people of the eastern counties (I daresay the term is more widely spread) call them "forty legs." This is not quite accurate, but as _Lithobius_ has 17 legs on each side, and _Scolopendra_ (_Cryptops_ is the English species) has 21 on each side, it is a better approximation than Centipede. But another country has a still more accurate term. I found some _Scolopendra_ in Beyrout, and asked my native servant what he called them. He gave them what I afterwards found was the common Arab name for them, "‘arba wál ‘arbarin," forty-four legs. Now the Scolopendras, which in hotter climates are the chief representatives of the Centipedes, have actually forty-two legs, or, if the poison claws are counted, forty-four. In looking up the Arab term for Centipede I came across a curious description given of them by Avicenna, the great Arabian physician: "This is an animal known for its habit of going into ears. For the most part it is a palm's length" [about four inches, which is the average length of many species]. "On each side of the body it has twenty-two feet, and moves equally well either backwards or forwards."

With regard to its alleged habit of going into ears, the learned Arabian has evidently made a false imputation on the character of our animal, and has probably relied too much on the stories told him. He has also exaggerated in stating that it goes equally well either backwards or forwards. Some Centipedes can go backwards very easily and well, though not so well as forwards. Perhaps he preferred examining dead specimens, which afford an easy opportunity of counting their legs, to experimenting with living animals, which might have resented liberties taken with them.

{42}The Persians have several words for them, less accurate than the Arabs and more like our own terms. For instance, they call them "Hazarpa," or thousand feet, like our Millepedes; also "Sadpa," or hundred feet, equivalent to our Centipedes. Another term resembles our common term before mentioned, "Chehlpa," forty feet. A more figurative term is "tasbih dud," a worm resembling a rosary with a hundred beads; this word is translated in Richardson's Persian Dictionary as "a venomous insect having eight feet and a piked tail."

CLASSIFICATION OF THE MYRIAPODA.

Two of the principal writers on the classification of the Myriapods are Koch and Latzel, both of whom have classified the whole group. I do not wish for a moment to undervalue the many authors who have done excellent work on the classification of different groups and families, but I wish here to give an outline of a classification of the whole class, and I naturally have recourse to the authors who have treated the subject as a whole.

Koch's two works, the _System der Myriapoden_[13] and _Die Myriapoden_,[14] cover the whole range of the class, and his divisions are clearly marked out and are easily understood, but both works are comparatively old. He does not include the Scolopendrellidae or the Pauropidae, which are now included by all naturalists in the Myriapoda. Latzel is a more recent writer, and though his work is entitled _The Myriapods of the Austro-Hungarian Empire_,[15] he gives much information about Myriapods not found in Europe, and his work is fairly entitled to be considered as embracing the whole class. He divides the Myriapods into four Orders, including the Scolopendrellidae and Pauropidae. On the whole, I think it will be better here to take the classification of Koch, and to add to it the two Orders before mentioned, viz. Symphyla containing one family the Scolopendrellidae, and Pauropoda with one family the Pauropidae.

The Orders are as follows:—

{43}Order I. CHILOGNATHA (= DIPLOPODA)

Antennae 7 joints, three anterior body rings with one pair of legs to each ring. Posterior rings with two pairs of legs to each. Genital organs opening ventrally on the anterior rings of the posterior part of the body, _i.e._ on one of the anterior of the segments bearing two pairs of legs; usually the 7th.

This Order is divided into eight families:—

Family 1. _Polyxenidae._

Ten body rings, not counting the neck-plate. Thirteen pairs of limbs.
Eyes hard to find, on the lateral corner of the head (Fig. 18, p. 37).

Family 2. _Glomeridae._

11 body rings. 17 pairs of legs. Eyes arranged in a row curved outwards.

Family 3. _Sphaerotheriidae._

12 body rings. 19 pairs of legs. Eyes crowded together in a cluster.

Family 4. _Julidae._

Body cylindrical. More than 30 body rings. Many eyes crowded together in
a cluster.

{44}Family 5. _Blanjulidae._

Thin cylindrical body with more than 30 body rings. Eyes either absent
or in a simple row beneath the edge of the forehead.

Family 6. _Chordeumidae._

Resemble the _Polydesmidae_ (Fam. 7), but the head is longer and less
rounded in the forehead. The antennae are placed more at the side of the
head. Eyes small and numerous, in a cluster. Body rings always 30 (Fig.
16).

Family 7. _Polydesmidae._

Body cylindrical, with a lobe or keel on the posterior part of the upper
surface of the body ring. Always 19 body rings. No eyes.

Family 8. _Polyzoniidae_.

Body with varying number of rings arched transversely downwards and sharp
at the sides. The anterior part of the ring somewhat hidden. The eyes in
a simple row. The stigmata very small and placed near the lateral corner
of the body ring. Head small in proportion to the body.

Order II. CHILOPODA (or SYNGNATHA).

Antennae with many joints, at least 14. Only one pair of legs to each body ring. The genital opening on the last ring of the body. Bases of the legs widely separate.

There are four families in this Order:—

{45}Family 1. _Lithobiidae._

Body with 9 principal and 6 subsidiary rings. On both principal and
subsidiary rings one pair of legs, except on the last ring of the body.
Many eyes; the posterior ones large and kidney-shaped. The antennae with
many rings.

Family 2. _Scolopendridae._

Body with 21 or 23 rings, no intermediate rings. Every ring with one pair
of legs. The last pair very long. Last pair at the point of the last
ring. Four or no eyes. Antennae with 17 or 20 joints. (Fig. 15, p. 31).

Family 3. _Notophilidae._

Body very long, 200 to 350 rings; alternate principal and subsidiary
rings. A pair of legs to each principal ring. No eyes. Maxillary palps
{46}very thick. Compact or very short limbs. The terminal point of the
last limb without claws.

Family 4. _Geophilidae._

Body long, 80 to 180 rings, principal and subsidiary. No eyes. The
maxillary palps not compact, and with first joint large. Last joint of
the last pair of legs with a sharp claw.

Order III. SCHIZOTARSIA.

The tarsi of all the legs multiarticulate. The eyes facetted. Peculiar sense organ beneath the head.

Family 1. _Cermatiidae_ (_Scutigeridae_)

Antennae with unequal number of joints. Body rings, each with one pair of
legs. Dorsal scutes not so large as ventral. Limbs long and
multiarticulate. (Fig. 17, p. 35).

Order IV. SYMPHYLA.

Myriapods resembling Thysanura. A pair of limbs to each segment. The antennae are simple and multiarticulate with unequal joints. Eyes few. Mandibles short. One pair of maxillae. No maxillipedes. Genital orifice in the last segment of the body. A single pair of tracheae. Two abdominal glands on the posterior part of the body. Two caudal appendages. Free dorsal scutes. Ventral scutes often with parapodia.

Family 1. _Scolopendrellidae._

With the characters of the Order.

{47}Order V. PAUROPODA.

A pair of limbs to each segment. Antennae branched. Eyes few or none. Labrum and labium indistinct. Genital orifice at the base of the second pair of limbs. Free dorsal scutes. Nine pairs of feet (always?). Some segments with sensitive hairs. Last segment the smallest.

Family 1. _Pauropidae._

Body slender. Dorsal scutes smooth. Limbs long and projecting from the
lateral margins of the body. Colour pale.

THE STRUCTURE OF THE MYRIAPODA.

Having now given a short view of the classification of the Class, I will proceed to give a general account of their structure, the variations in which have led to the divisions into the various Orders and Families. Their structure shows resemblances to several widely different classes of animals. One cannot help being impressed with their likeness to the Worms, at the same time they have affinities with the Crustaceans, and still more with the Insects. In the latter class the likeness of the Thysanuridae to _Scolopendrella_ and _Pauropus_ have induced a celebrated Italian anatomist, Professor Grassi, to claim the former as the ancestors of the Myriapoda.

Myriapods have a body which is segmented, as it is termed; that is, composed of a number of more or less similar parts or segments joined together.

One of the most important characteristics which distinguish Myriapods from other Arthropoda is the fact that they possess on the posterior segments of the body true legs which are jointed and take part in locomotion. The head is in all cases quite distinct from the body, and may be regarded as a number of segments fused together into one mass. Their heads are always provided with a single pair of _antennae_ and mouth appendages, consisting of an upper lip, a pair of _mandibles_ or jaws, and one to two pairs of _maxillae_. The mandibles resemble those of Insects, and are strongly toothed. In the Chilognatha a pair of maxillae are fused so as to form a single oval appendage. In the Chilopoda they each consist of a single blade bearing a {48}short palp or feeler. The mouth parts may have the forms known as chewing, biting, or suctorial (_Polyzonium_) mouth appendages.

With the exception of the terminal segment, and in many cases the first or the seventh, each segment bears one or two pairs of limbs. These may be very long, as in _Scutigera_, or very short, as in _Polyxenus_. They may be attached close to one another near the ventral middle line of the body, or may have their bases far apart from each other, as in the Chilopoda. The exoskeleton or external armour is composed of chitin (Chilopoda) or of chitin with calcareous salts deposited in it (Chilognatha).

Their internal structure has a great likeness to that of Insects.

The general position of the internal organs may be seen from Fig. 28, which shows a _Lithobius_ dissected so as to exhibit the digestive and nervous systems.

_The digestive canal_, which is a straight tube, extends throughout the whole length of the body, and terminates in the last segment of the body. It may be divided into the following parts:—

1. A narrow oesophagus, beginning with the mouth or buccal cavity, and
receiving the contents of two or more salivary glands (_d_).

2. A wide mesenteron or mid-gut (_n_) extending throughout almost the
whole length of the body.

3. A rectum which at its junction with the mid-gut receives the contents
of two or four _Malpighian tubes_ (_g_, _h_) which function as kidneys.
Their function was for a long time unknown, but the discovery of crystals
of uric acid in them placed the matter beyond doubt.

_The heart_ has the form of a long pulsating dorsal vessel which extends through the whole length of the animal. It is divided into a number of chambers, which are attached to the dorsal wall of the body, and are furnished with muscles of a wing-like shape, which are known as the alary muscles, and which govern its pulsations. The chambers are furnished with valves and arteries for the exit of the blood, and slits known as _ostia_ for the return of the blood to the heart. The blood enters the chambers of the heart from the body cavity through the {49}ostia, and passes out through the arteries to circulate through the organs of the body and to return by the ostia.

The two figures below (Figs. 29 and 30) show the position of the arteries and the ostia in a single segment of the body. The heart is too small and delicate to be seen with the naked eye; it therefore requires the aid of the microscope. A freshly-killed animal was therefore taken and prepared in the manner known to all microscopists, and extremely thin slices or sections cut horizontally from its back. One of these sections cut the whole length of the heart in one segment, which was accordingly drawn under the microscope (Fig. 29), and shows a longitudinal {50}horizontal section through the whole length of the heart in a single segment, with the two ostia at each end of the segment and the two arteries in the middle.

The arteries, when they leave the body, pass into masses of fatty tissue on either side of the heart, and the other figure (Fig. 30) is intended to show the artery leaving the heart and penetrating into the fatty tissue. The figure is taken from the same section as the former one, but is much more highly magnified, so as to show more detail. The delicate coats of the heart are shown, the artery being covered with a clothing of large cells.

Myriapods breathe by means of _tracheae_, with the exception of the Scutigeridae, which have an elementary form of lung which resembles that of spiders, and will be mentioned further on. These tracheae, as in Insects, are tubes lined with chitin, which is arranged in spiral bands. The tracheae open to the exterior by openings called _stigmata_, through which they receive the external air, which passes into the main tracheal tubes and into their ramifications, and thus effects the aeration of the blood.

The _nervous system_ of the Myriapods consists, as in Insects, of a brain, which may be more or less developed, a circumoesophageal ring embracing the oesophagus, and a ventral chain of ganglia, and in some cases (Newport) of a system of visceral {51}nerves. With the nervous system we may mention the sense organs, the eyes, which are present in most cases, though wanting, as has been already stated, in many groups. They are usually present as clusters of ocelli or eye spots closely packed together, or (in _Scutigera_) as peculiarly formed facetted eyes. The sensory hairs on the antennae must be reckoned as sense organs, as also the tufts of sense hairs on the head of _Polyxenus_. _Scutigera_ has also a peculiar sense organ beneath the head, consisting of a sac opening on the under side of the head full of slender hairs, each of which is connected at its base with a nerve fibre. Except the eyes, the Myriapod sense organs have usually the form of hairs or groups of hairs connected with nerve fibres, which communicate with the central nervous system.

These two sense organs are shown in Figs. 31 and 32. Fig. 31 shows the under side of the head of _Scutigera_ (Fig. 17), with the position of the sense organ and its opening. Fig. 32 is part of a section through the head of _Polyxenus_ with two of the sense hairs. Each spine or sense hair fits into a cup in the chitin of the head; and the lower or internal part, which is divided from the upper or external part by a rim, is joined to a ganglionic nerve cell (_gang.c._).

The Myriapods are of separate sexes, and the generative organs in both cases usually have the form of a long unpaired {52}tube, which in the male is connected with accessory glands, and in the female is usually provided with double receptacula seminis. The generative openings usually lie near the base of the second pair of legs (Chilognatha), or at the posterior end of the body (Chilopoda). In the Chilognatha there is usually in the male an external copulatory organ at the base of the seventh pair of legs, remote from the genital opening.

The preceding account of the anatomy of the Myriapods has shown us the general characteristics of the whole group. I shall now take each of the five Orders into which the class is divided in the classification adopted in this account, and endeavour to explain the differences in anatomy which have led to the establishment of the Order. The first Order with which we have to do is that of the Chilognatha, which includes a large number of Myriapods; no less than eight families, some of them including a great number of forms.

ORDER I. CHILOGNATHA.

The Chilognatha differ from other Orders in the shape of the body. This is in almost all cases, cylindrical or sub-cylindrical, instead of being more or less flattened as in the other Orders.

The body, as in all other Myriapods, is composed of segments, but in the Chilognatha these segments are composed, in almost all cases, of a complete ring of the substance of which the exoskeleton (as the shell of the animal is called) is composed. This substance is in the case of the Chilognatha chitin (a kind of horny substance, resembling, for instance, the outer case of a beetle's wing), containing a quantity of chalk salts and colouring matter; the substance thus formed is hard and tough. In other Orders the chitin of the exoskeleton is without chalky matter and is much more flexible. The length of the body, as may be seen from the classification, may be either very long, as in _Julus_, or very short, as in _Glomeris_.

The next anatomical character distinctive of the Order is the form of the appendages. First, the antennae. These are, as a general rule, much shorter than in the Chilopods, never reaching the length of half the body. They are, as a rule, club-shaped, the terminal half being thicker than the half adjoining the body.

{53}The next appendages to be mentioned are the _mouth parts_. These differ in form from those of the other Orders, and their differences are connected very largely with the fact that the Chilognatha live on vegetable substances. Their mouth parts are adapted for chewing, except in the case of the Polyzoniidae, the eighth family of the Order, in which, according to Brandt, the mouth parts are adapted for sucking, and are prolonged into a kind of proboscis. The mouth parts of the Chilognatha consist of—

(1) _An upper lip._ A transversely-placed plate, which is fused with the
rest of the head.

(2) A pair of powerful mandibles or jaws adapted for mastication, and
moved by powerful muscles. _f_ and _g_ in Fig. 33 shows these mandibles,
while the rest of the figure constitutes the broad plate (No. 3).

(3) A broad plate covering the under part of the head and partially
enclosing the mouth. This structure, which, as we shall afterwards see,
is formed by the fusion of two appendages which are distinct in the
animal when just hatched, has been called the deutomalae, the jaws
receiving the name of protomalae.

After the mouth parts we come to the legs. We first notice the fact that the bases of the legs in each pair are closely approached to one another. They are so set into the body that the basal joints, or, as they are called, the coxal joints, nearly touch. This is the case in almost all Chilognatha, except in the Polyxenidae, and it is a fact connected with some important features in the internal anatomy. Then we have the peculiarity in the Chilognatha which has formed the basis of most classifications which have placed these animals in a group by themselves. This is the possession in most segments of two pairs of legs. This characteristic has caused the group to be called by some naturalists Diplopoda. As a general rule, the first four segments {54}have only three pairs of legs between them, one of them being without a pair of legs. This legless or apodal segment is usually the third. From the fifth segment to the end of the body all the segments have two pairs of legs each. The legs are shorter than those of the Chilopods, and are all nearly equal in size. This is not the case in the other Orders. The legs are commonly wanting in the seventh segment of the male, and are replaced by a copulatory organ. This peculiarity is related to the different position of the generative openings in the Chilognatha. Another anatomical feature peculiar to the Chilognatha is the possession of the stink glands—the _glandulae odoriferae_ before mentioned. This, however, is a character which does not hold for all the Chilognatha, since the Polyxenidae have none of these glands. All the other families, however, possess them, and they are present in none of the other Orders.

As regards the internal anatomy of the Chilognatha, the _digestive canal_ differs mainly in the glands which supply it with secretions. It receives the saliva from two long tubular salivary glands, which open at the base of the four-lobed plate which has been mentioned as the third of the mouth appendages. The secretion of these glands is used, as has already been said, in the process of preparing the nest for the eggs. We cannot fail to be reminded of a similar function of salivary glands in those swallows, which prepare the nests of which bird's-nest soup is made with the secretion of the salivary glands. Another feature in the form of the digestive tube is that in many cases, if not in all, it is marked with constrictions which correspond with the segments of the body.

The _heart_ in the Chilognatha is not such a highly developed organ as in the other Orders. The muscles which have already been mentioned as the _alary_ muscles (or wing-shaped muscles) are not so highly developed, and consist for the most part of a few muscular fibres. The muscular walls of the heart, which consist of three layers, have the muscles less strongly developed, and are in general adapted for a less energetic circulation.

The _tracheae_, which open into the stigmata, as has already been said, branch into tufts of fine tubes, but the ramifications of these tufts never join (or anastomose, as it is called), and consequently we never get, as in the other Orders, long tracheal trunks running along the body.

{55}The _nervous system_, in addition to the existence of the visceral nerve system described by Newport, shows a marked peculiarity in the form of the ventral ganglionic chain. As has already been said, the nerve system consists of a brain or mass of ganglia fused together and connected with the ventral nervous cord by a collar of nervous substance surrounding the oesophagus, and generally known as the _circumoesophageal_ collar. The ventral nerve cord is a stout cord of nervous substance passing along the whole length of the animal, and situated below (or ventral to) the digestive tube and the generative system. This cord is enlarged at certain points, and these enlargements or swellings are called ganglia, while from the ganglia pass off nerves which supply the different organs of the body. In the Chilognatha the cord has a compressed appearance as if the ganglia were pressed into one another in such a way that it is very hard to distinguish any ganglia at all. If we use the microscope and examine sections cut transversely through the cord, we see that it is not a simple cord. Even if we examine the nerve cord with a simple lens, we see that a furrow runs longitudinally down it, and the use of the compound microscope shows us that this furrow represents a division into two cords in such a way that the single stout cord as it appeared to the naked eye is in reality two cords running side by side, and so compressed together that the substance is partly fused together. The ganglia too are double, being swellings of the two cords and not a single enlargement on a single cord. As we shall see in the other Orders, this arrangement constitutes a characteristic distinction.

The _generative organs_ consist of a long tubular ovary or testis lying along almost the whole length of the body and placed between the digestive organ and the nervous system. Near its exit from the body the long tube divides into two short tubes, the oviducts in the female or the vasa _deferentia_ in the male. These ducts open in the third segment of the body, unlike those of Myriapods belonging to other Orders. The accessory glands present in most other Myriapods are not present in the Chilognatha.

The general arrangement of the organs of the Chilognatha may be seen from Fig. 34, which represents a transverse section through the body of _Polyxenus_ (Fig. 18). A comparison of {56}these two figures (Figs. 34 and 18) will show the position of the organs mentioned in this account. The heart is shown with the suspensory and alary muscles attached.

ORDER II. CHILOPODA.

The shape of the body differs from that of the Order which has been just described (Chilognatha), inasmuch as it is not cylindrical but flattened, the back, however, being more arched than the ventral surface. In this respect, however, it cannot be said to differ from the other Orders which we have yet to describe.

The segments are not formed by a single ring of the exoskeleton, which in this Order is formed of chitin, and is tough and flexible rather than hard and strong; but of two or three plates which form a covering to the segment. The back is covered by a large plate known as the _tergum_, the sides by two plates known as _pleura_, and the ventral part by a plate called the _sternum_. The pleura and sternum are, however, in most cases fused together or indistinguishable. In this, as in most of the anatomical peculiarities, there is a much greater difference between the two Orders Chilopoda and Chilognatha than between {57}the Chilopoda and the other three Orders which have still to be described.

The Chilopoda have only one pair of appendages to each segment of the body instead of two pairs like the Chilognatha.

The antennae of the Chilopoda are as a rule very long, and are always longer than in the Chilognatha which we have just described. They differ from those of the Schizotarsia (the third Order, which will be the next to be described) in having the basal joints nearer together; in other words, they are differently placed on the head. They differ from those of the Pauropoda (the fifth Order) in being straight and not branched. As a rule the antennae of the Chilopoda taper towards the extremity.