“As the accuracy of the census to be obtained by Congress will necessarily depend in a considerable degree on the disposition if not co-operation of the states, it is of great importance that the states should feel as little bias as possible to swell or reduce theamount of their numbers. Were their share of representation alone to be governed by this rule, they would have an interest in exaggerating their inhabitants. Were the rule to decide their share of taxation alone, a contrary temptation would prevail. By extending the rule to both objects the states will have opposite interests, which will control and balance each other, and produce a requisite impartiality.”
“As the accuracy of the census to be obtained by Congress will necessarily depend in a considerable degree on the disposition if not co-operation of the states, it is of great importance that the states should feel as little bias as possible to swell or reduce theamount of their numbers. Were their share of representation alone to be governed by this rule, they would have an interest in exaggerating their inhabitants. Were the rule to decide their share of taxation alone, a contrary temptation would prevail. By extending the rule to both objects the states will have opposite interests, which will control and balance each other, and produce a requisite impartiality.”
With the disappearance of direct taxation as a source of federal revenue, the motive mentioned for understating the population disappeared. On the other hand, the desire for many representatives in Congress has been reinforced by the more influential feelings of local pride and of rivalry with other cities of somewhat similar size. Hence a complaint that the population is overstated is seldom heard, and hence, also, popular charges of an under-count afford little evidence that the population was really larger than stated by the census.
After the detailed tabulation had been completed, it was shown that the number of persons under ten years of age in 1890 was surprisingly small, and that this deficiency in children was a leading cause of the slow growth in population. Before the tabulation had been made Francis A. Walker wrote:—“If the birth-rate among the previously existing population did not suffer a sharp decline ... the census of 1890 cannot be vindicated. To ascertain the facts we must await the tabulation of the population by periods of life, and ascertain how many of the inhabitants of the United States of 1890 were under ten years of age.” These results thus confirmed the accuracy of the count of 1890. Efforts to invalidate the census returns by comparison with the registration records of Massachusetts cannot be deemed conclusive, since in the United States, as in Great Britain, the census must be deemed more accurate and less subject to error than registration records. A strong argument in favour of the eleventh census, apart from its self-consistency, is that its results as a whole fit in with the subsequent state enumerations. In eleven cases such enumerations have been taken; and on computing from them and the results of the federal census of 1880 what the population at the date of the eleventh census should have been, if the annual rate of increase had been uniform, it appears that in no case, except New York City and Oregon, was the difference between the enumerations and these estimates over 4%. In Oregon about 30,000 more people were found in 1890 than the estimate would lead one to expect; in New York city, about 100,000 less. It seems not improbable that in the latter, where the difficulties incident to a count during the summer are almost insurmountable, serious omissions occurred. Still, such a comparison confirms the accuracy of the eleventh census as a whole.
The results of the twelfth census (1900) further refute the argument that would maintain the eleventh census to be inaccurate because it showed a smaller rate of increase in population during the preceding decade than had been recorded by other censuses during earlier decades. The rate of increase during the decade ending in 1900 was even less than that for the preceding decade; and it is impossible that a falling off so marked could in two successive enumerations be the result of sheer inaccuracy. The rate of increase from 1890 to 1900, eliminating from the computation the population of Alaska, Hawaii, Indian Territory and Indian reservations, was 20.7; the rate of increase if these places are included—in which case the figures of the population of Hawaii in 1890 must be taken from the census of the Hawaiian government in that year—was 21%.
The law regulating the twelfth census deserves to rank with those of 1790, 1850 and 1879 as one of the four important laws relative to census work. By this law the census office was far more independent than ever before. Appointments and removals were made by the director of the census rather than by the secretary of the interior, and in all plans for the execution of the law the head of the office was responsible for success. The law divided the subjects of census inquiry into two parts—first, those of primary importance, requiring the aid of the enumerator; and, secondly, those of subsidiary importance, capable of production without the aid of the enumerator. The former had to be finished and published by 1st July 1902; the latter were not to be undertaken until the former were well advanced towards completion. By this means the attention of the office could be concentrated on a small number of subjects rather than distributed over the long list treated in the volumes of the tenth and eleventh censuses.Under the federal form of government, with its delegation of all residuary powers to the several states, the United States have no system of recording deaths, births and marriages. Hence there is no such basis as exists in nearly every other civilized state for a national system of registration, and the country depends upon the crude method of enumerators’ returns for its information on vital statistics, except in the states and cities which have established a trustworthy registration system of their own. These are the New England states and a few others in their vicinity or influenced by their example. Enumerators’ returns in this field are so incomplete that hardly two-thirds of the deaths which have occurred in any community during the preceding year are obtained by an enumerator visiting the families, no satisfactory basis for the computation of death-rates is afforded, and the returns have comparatively little scientific value. In the regions where census tables and interpretations are derived from registration records kept by the several states or cities they are often made more complete than those in the state or municipal documents. The census of agriculture is also liable to a wide margin of error, owing to defects in farm accounts and the inability of many farmers to state the amount or the value even of the leading crops. The census figures relate to the calendar year preceding 1st June 1900, and hurried and careless answers about the preceding year’s crop are almost sure to have been given by many farmers in the midst of the summer’s work.The difficulties facing the manufacturing census were of a different character. A large proportion of the industries of the country keep satisfactory accounts, and can answer the questions with some correctness. But manufacturers are likely to suspect the objects of the census, and to fear that the information given will be open to the public or betrayed to competitors. Furthermore, the manufacturing schedule presupposes some uniformity in the method of accounting among different companies or lines of business, and this is often lacking. Another source of error in the manufacturing census of the United States is that the words of the census law are construed as requiring an enumeration of the various trades and handicrafts, such as carpentering. The deficiencies in such returns are gross and notorious, but the census office feels obliged to seek for them and to report what it finds, however incomplete or incorrect the results may be. Even on the population returns certain answers, such as the number of the divorced or the number unable to read and write, may be open to question.The wide range of the American census, and the publication of uncertain figures, find a justification in the fact that the development of accurate census work requires a long educational process in the office, and, above all, in the community. Rough approximations must always precede accurate measurements; and these returns, while often inaccurate, are better than nothing, and probably improve with each decade.Besides, the breadth of its scope, in which the American census stands unrivalled, the most important American contribution to census work has been the application of electricity to the tabulation of the results, as was first done in 1890. The main difficulties which this method reduced were two. The production of tables for so enormous a population as that of the United States through the method of tallying by hand requires a great number of clerks and a long period of time, and when complete cannot be verified except by a repetition of the process. The new method abbreviates the time, since an electric current can tally almost simultaneously the data, the tallying of which by hand would be separated by appreciable intervals. The method also renders comparatively easy the verification of the results of certain selected parts.Judged by European standards the cost of the American census is very great. The following table gives the total and the per capita cost of each enumeration.Date.Cost.Date.Cost.Total indollars.Per Capitain cents.Total indollars.Per Capitain cents.179044,3771.1218501,423,3516.13180066,1091.2418601,969,3776.261810178,4452.4618703,421,1988.871820208,5262.1618805,790,67811.481830378,5452.94189011,547,12718.331840833,3714.88190016,116,93021.16For the sake of comparison it may be stated that the per capita cost of the English census of 1901 was 2.24 cents, or little more than one-tenth that of the American census. This difference is due in part to the greater scope and complexity of the American census, and in part to the fact that in the United States the field work is done by well-paid enumerators, while in England it is done in most cases by the heads of families, who are not paid.The course of events has clearly established the fact that the authority of the Federal government in this field is greater than the strict constructionists of a previous generation as representedby General Walker in the passage already quoted believed it to be. Decision after decision of individual instances has made it a settled practice for the Federal government to co-operate with or to supplement the state governments in the gathering of statistics that may furnish a basis for state or Federal legislation. The law has allowed the Federal census office in its discretion to compile and publish the birth statistics of divisions in which they are accurately kept; one Federal report on the statistics of marriages and divorces throughout the country from 1867 to 1886 inclusive was published in 1889, and a second for the succeeding twenty-year period was published in 1908-1909; an annual volume gives the statistics of deaths for about half the population of the country, including all the states and cities which have approximately complete records of deaths; Federal agencies like the bureau of labour and the bureau of corporations have been created for the purpose of gathering certain social and industrial statistics, and the bureau of the census has been made a permanent statistical office.The Federal census office has been engaged in the compilation and publication of statistics of many sorts. Among its important lines of work may be mentioned frequent reports during the cotton ginning season upon the amount of cotton ginned, supplemental census reports upon occupations, on employees and wages, and on further interpretation of various population tables, reports on street and electric railways, on mines and quarries, on electric light and power plants, on deaths in the registration area 1900-1904, on benevolent institutions, on the insane, on paupers in almshouses, on the social statistics of cities and on the census of manufactures in 1905. Congress has recently entrusted it with still further duties, and it has developed into the main statistical office of the Federal government, finding its nearest analogue probably in the Imperial Statistical Office in Berlin.
The law regulating the twelfth census deserves to rank with those of 1790, 1850 and 1879 as one of the four important laws relative to census work. By this law the census office was far more independent than ever before. Appointments and removals were made by the director of the census rather than by the secretary of the interior, and in all plans for the execution of the law the head of the office was responsible for success. The law divided the subjects of census inquiry into two parts—first, those of primary importance, requiring the aid of the enumerator; and, secondly, those of subsidiary importance, capable of production without the aid of the enumerator. The former had to be finished and published by 1st July 1902; the latter were not to be undertaken until the former were well advanced towards completion. By this means the attention of the office could be concentrated on a small number of subjects rather than distributed over the long list treated in the volumes of the tenth and eleventh censuses.
Under the federal form of government, with its delegation of all residuary powers to the several states, the United States have no system of recording deaths, births and marriages. Hence there is no such basis as exists in nearly every other civilized state for a national system of registration, and the country depends upon the crude method of enumerators’ returns for its information on vital statistics, except in the states and cities which have established a trustworthy registration system of their own. These are the New England states and a few others in their vicinity or influenced by their example. Enumerators’ returns in this field are so incomplete that hardly two-thirds of the deaths which have occurred in any community during the preceding year are obtained by an enumerator visiting the families, no satisfactory basis for the computation of death-rates is afforded, and the returns have comparatively little scientific value. In the regions where census tables and interpretations are derived from registration records kept by the several states or cities they are often made more complete than those in the state or municipal documents. The census of agriculture is also liable to a wide margin of error, owing to defects in farm accounts and the inability of many farmers to state the amount or the value even of the leading crops. The census figures relate to the calendar year preceding 1st June 1900, and hurried and careless answers about the preceding year’s crop are almost sure to have been given by many farmers in the midst of the summer’s work.
The difficulties facing the manufacturing census were of a different character. A large proportion of the industries of the country keep satisfactory accounts, and can answer the questions with some correctness. But manufacturers are likely to suspect the objects of the census, and to fear that the information given will be open to the public or betrayed to competitors. Furthermore, the manufacturing schedule presupposes some uniformity in the method of accounting among different companies or lines of business, and this is often lacking. Another source of error in the manufacturing census of the United States is that the words of the census law are construed as requiring an enumeration of the various trades and handicrafts, such as carpentering. The deficiencies in such returns are gross and notorious, but the census office feels obliged to seek for them and to report what it finds, however incomplete or incorrect the results may be. Even on the population returns certain answers, such as the number of the divorced or the number unable to read and write, may be open to question.
The wide range of the American census, and the publication of uncertain figures, find a justification in the fact that the development of accurate census work requires a long educational process in the office, and, above all, in the community. Rough approximations must always precede accurate measurements; and these returns, while often inaccurate, are better than nothing, and probably improve with each decade.
Besides, the breadth of its scope, in which the American census stands unrivalled, the most important American contribution to census work has been the application of electricity to the tabulation of the results, as was first done in 1890. The main difficulties which this method reduced were two. The production of tables for so enormous a population as that of the United States through the method of tallying by hand requires a great number of clerks and a long period of time, and when complete cannot be verified except by a repetition of the process. The new method abbreviates the time, since an electric current can tally almost simultaneously the data, the tallying of which by hand would be separated by appreciable intervals. The method also renders comparatively easy the verification of the results of certain selected parts.
Judged by European standards the cost of the American census is very great. The following table gives the total and the per capita cost of each enumeration.
For the sake of comparison it may be stated that the per capita cost of the English census of 1901 was 2.24 cents, or little more than one-tenth that of the American census. This difference is due in part to the greater scope and complexity of the American census, and in part to the fact that in the United States the field work is done by well-paid enumerators, while in England it is done in most cases by the heads of families, who are not paid.
The course of events has clearly established the fact that the authority of the Federal government in this field is greater than the strict constructionists of a previous generation as representedby General Walker in the passage already quoted believed it to be. Decision after decision of individual instances has made it a settled practice for the Federal government to co-operate with or to supplement the state governments in the gathering of statistics that may furnish a basis for state or Federal legislation. The law has allowed the Federal census office in its discretion to compile and publish the birth statistics of divisions in which they are accurately kept; one Federal report on the statistics of marriages and divorces throughout the country from 1867 to 1886 inclusive was published in 1889, and a second for the succeeding twenty-year period was published in 1908-1909; an annual volume gives the statistics of deaths for about half the population of the country, including all the states and cities which have approximately complete records of deaths; Federal agencies like the bureau of labour and the bureau of corporations have been created for the purpose of gathering certain social and industrial statistics, and the bureau of the census has been made a permanent statistical office.
The Federal census office has been engaged in the compilation and publication of statistics of many sorts. Among its important lines of work may be mentioned frequent reports during the cotton ginning season upon the amount of cotton ginned, supplemental census reports upon occupations, on employees and wages, and on further interpretation of various population tables, reports on street and electric railways, on mines and quarries, on electric light and power plants, on deaths in the registration area 1900-1904, on benevolent institutions, on the insane, on paupers in almshouses, on the social statistics of cities and on the census of manufactures in 1905. Congress has recently entrusted it with still further duties, and it has developed into the main statistical office of the Federal government, finding its nearest analogue probably in the Imperial Statistical Office in Berlin.
(W. F. W.)
CENTAUREA,in botany, a genus of the natural order Compositae, containing between four and five hundred species, and of wide distribution, but with its principal centre in the Mediterranean region. The plants are herbs with entire or cut often spiny-toothed leaves, and ovoid or globose involucres surrounding a number of tubular, oblique or two-lipped florets, the outer of which are usually larger and neuter, the inner bisexual. Four species are native in Britain.C. nigrais knapweed, common in meadows and pastureland;C. Cyanusis the bluebottle or cornflower, a well-known cornfield weed;C. Calcitrapais star-thistle, a rare plant, found in dry waste places in the south of England, and characterized by the rose-purple flower-heads enveloped by involucral bracts which end in a long, stiff spine. Besides cornflower, a few other species are worth growing as garden plants; they are readily grown in ordinary soil:—C. Cineraria, a half-hardy perennial, native of Italy, is remarkable for its white downy foliage;C. babylonica(Levant) has large downy leaves and a tall spike of small yellow flowers;C. dealbata(Caucasus) is a low-growing plant with larger rose-coloured heads;C. macrocephala(Caucasus) has large yellow heads;C. montana(Pyrenees) large handsome blue heads; andC. ragusina(S.E. Europe) beautiful silver-haired leaves and yellow flowers.
CENTAURS,in Greek mythology, a race of beings part horse part man, dwelling in the mountains of Thessaly and Arcadia. The name has been derived (1) fromκεντεῖν(goad) andταῦρος(bull), implying a people who were primarily herdsmen, (2) fromκεντεῖνand the common termination-αυροςorαὔρα(“air”)i.e.“spearmen.” The former is unsatisfactory partly from the philological standpoint, and the latter, though not certain, is preferable. The centaurs were the offspring of Ixion and Nephele (the rain-cloud), or of Kentauros (the son of these two) and some Magnesian mares or of Apollo and Hebe. They are best known for their fight with the Lapithae, caused by their attempt to carry off Deidameia on the day of her marriage to Peirithous, king of the Lapithae, himself the son of Ixion. Theseus, who happened to be present, assisted Peirithous, and the Centaurs were driven off (Plutarch,Theseus, 30; Ovid,Metam.xii. 210; Diod. Sic. iv. 69, 70). In later times they are often represented drawing the car of Dionysus, or bound and ridden by Eros, in allusion to their drunken and amorous habits. Their general character is that of wild, lawless and inhospitable beings, the slaves of their animal passions, with the exception of Pholus and Chiron. They are variously explained by a fancied resemblance to the shapes of clouds, or as spirits of the rushing mountain torrents or winds. As children of Apollo, they are taken to signify the rays of the sun. It is suggested as the origin of the legend, that the Greeks in early times, to whom riding was unfamiliar, regarded the horsemen of the northern hordes as one and the same with their horses; hence the idea of the Centaur as half-man, half-animal. Like the defeat of the Titans by Zeus, the contests with the Centaurs typified the struggle between civilization and barbarism.
In early art they were represented as human beings in front, with the body and hind legs of a horse attached to the back: later, they were men only as far as the waist. The battle with the Lapithae, and the adventure of Heracles with Pholus (Apollodorus, ii. 5; Diod. Sic. iv. II) are favourite subjects of Greek art (see Sidney Colvin,Journal of Hellenic Studies, i. 1881, and the exhaustive article in Roscher’sLexikon der Mythologie). Fig. 34 in articleGreek Art(the west pediment of the temple of Zeus at Olympia) represents the attempt of the Centaurs to carry off the bride of Peirithous.
In early art they were represented as human beings in front, with the body and hind legs of a horse attached to the back: later, they were men only as far as the waist. The battle with the Lapithae, and the adventure of Heracles with Pholus (Apollodorus, ii. 5; Diod. Sic. iv. II) are favourite subjects of Greek art (see Sidney Colvin,Journal of Hellenic Studies, i. 1881, and the exhaustive article in Roscher’sLexikon der Mythologie). Fig. 34 in articleGreek Art(the west pediment of the temple of Zeus at Olympia) represents the attempt of the Centaurs to carry off the bride of Peirithous.
CENTAURUS(“The Centaur”), in astronomy, a constellation of the southern hemisphere, mentioned by Eudoxus (4th centuryb.c.) and Aratus (3rd centuryb.c.), Ptolemy catalogued thirty-seven stars in it.α-Centauriis a splendid binary star. Its components are of the 1st magnitude, and revolve in a period of eighty-one years; and since its parallax is 0.75″, it is the nearest star to the earth;ω-Centauri, the finest globular star-cluster in the heavens, consists of about 6000 stars in a space of about 20′ diameter, of which about 125 variables have been examined.Nova Centauri, a “new” star, was discovered in 1895 by Mrs Fleming in photographs taken at Harvard.
CENTAURY(Erythraea Centaurium, natural order Gentianaceae), an annual herb with erect, smooth stem, usually branched above, and a terminal inflorescence with numerous small red or pink regular flowers with a funnel-shaped corolla. The plant occurs in dry pastures and on sandy coasts in Britain, and presents many varieties, differing in length of stem, degree of branching, width and shape of leaves, and laxity or closeness of the inflorescence. Several other species of the genus are grown as rock-plants.
CENTENARY(from Lat.centenarius, of or belonging to a hundred, fromcenteni, distributive ofcentum, hundred), a space of a hundred years, and particularly the celebration of an event on the lapse of a hundred years, a centennial anniversary. The word “centennial” (from Lat.centennis, fromcentum, andannus, a year), though usually an adjective as in “the Centennial State,” the name given to Colorado on its admission to statehood in 1876, is also used as a synonym of centenary.
CENTERVILLE,a city and the county-seat of Appanoose county, Iowa, U.S.A., in the south part of the state, about 90 m. N.W. of Keokuk. Pop. (1890) 3668; (1900) 5256; (1905, state census) 5967 (487 being foreign-born); (1910) 6936. Centerville is served by the Chicago, Burlington & Quincy, the Chicago, Rock Island & Pacific and the Iowa Central railways. Among the principal buildings are the county court-house and the Federal building, and the city has a public library and a hospital. It is in one of the most productive coal regions of the state; it ships coal, limestone and livestock, has large bottling works, and manufactures iron, brick and tile, machine-shop products, woollen goods, shirts, cigars and flour. The place was platted in 1846, was called Chaldea until 1849, when the present name was adopted, was incorporated as a town in 1855, and in 1870 was chartered as a city of the second class. The city limits were extended in 1906-1907.
CENTIPEDE,the characteristic member of the group Chilopoda, a class of the Arthropoda, formerly associated with the Diplopoda (Millipedes), the Pauropoda and the Symphyla, to constitute the now abandoned group Myriapoda. The resemblance between the Chilopoda and the Diplopoda is principally superficial and due to the elongation and vermiform shape of the body, which in both is composed of a number of similar or subsimilar somites not differentiated as are those of Insecta, existing Arachnida and most Crustacea, into series or “tagmata” of varying function. Until 1893 no one doubted the correctness of the assumption that the Chilopoda and Diplopoda were orders of a class Myriapoda of the same systematic status as the Arachnida or Hexapoda. But in that year, R.I. Pocock and J.S. Kingsley independently pointed out that they differ as much from each other as either differs from the Hexapoda; and should, therefore,rank as distinct classes of Arthropods. Pocock, indeed, definitely associated the Chilopoda with the Hexapoda in a group, the Opisthogoneata (Opisthogonea), equivalent to a group, the Progoneata (Prosogonea), comprising the Diplopoda, Pauropoda and Symphyla. As the basis for this classification was taken the position of the generative orifices which open in the Opisthogonea at the posterior end and in the Prosogonea near the anterior end of the body. As a matter of fact, in the Chilopoda they are situated on the penultimate or pretelsonic somite; in the Hexapoda upon the antepenultimate somite (male) or a little farther forward (female). Moreover, the recent researches of Heymons into the embryology ofScolopendra, one of the Chilopods, has shown a close correspondence in the number of cephalic metameres between the Chilopoda and Hexapoda, a correspondence which has not yet been established in the case of the Diplopoda or Symphyla. This last discovery bears out the view of relationship between the centipedes and insects, to the exclusion of the Diplopoda, Symphyla and Pauropoda. But even if in the future it can be shown that all these groups can be brought into line with respect to the metamerism of the head, the position of the generative orifices will remain as a fundamental and constant character, distinguishing the Chilopoda from the other groups of so-called “Myriapods” and the Hexapoda from the Symphyla, which in many particulars they resemble.
Structure of the Chilopoda.—The exoskeletal elements of a typical somite consist of a dorsal plate or tergum, a ventral plate or sternum, a lateral or pleural membrane, often strengthened with chitinous sclerites, and a pair of appendages. At the anterior extremity there is a head-shield or cephalite, which bears eyes, when present, and a pair of antennae. In all centipedes, except theScutigeridae, the preantennal portion of the cephalite is sharply reflexed, ventrally forming an area called the clypeus. The inferior edge of this bears the labrum, which is usually represented by a small median, and two large lateral plates. The appendages are modified as a single pair of antennae, four pairs of jaws or gnathites, a variable number of walking legs and a single pair of generative limbs or gonopods. The antennae, articulated to the forepart of the head and preoral in position, are long and flexible and consist of fourteen or more segments. The jaws of the first pair of mandibles are stout and bi-segmented, with a dentate cutting edge. Those of the second pair or maxillae vary considerably in structure in different groups. They are foliaceous and are usually regarded as biramous. In some genera (Scutigera,Lithobius) the inner branch consists of two distinct segments meeting those of the opposite side in the middle line. The outer branch, which is always larger, consists of three or four segments. Generally, however, the basal segments of the two branches are coalesced with each other and with the corresponding segments of the opposite side to form a single broad transverse plate. The above described condition seen inScutigerasuggests that two pairs of jaws may be involved in the formation of the maxillae in the Chilopoda. The jaws of the third pair, the palpognaths or second pair of maxillae, resemble dwarfed walking legs, and consist of five or six segments, of which the basal or coxa is united mesially to its fellow. The jaws of the fourth pair, the toxicognaths or poison-jaws, are long and powerful, and consist like the legs primarily of six segments, whereof the basal is large and usually fused with its fellow to form a large coxal plate, the second is small and generally suppressed by fusion with the third, the fourth and fifth are also small, while the sixth is transformed into a great piercing fang, at the tip of which opens the duct of a poison gland lodged within the appendage.The tergal elements of the somites bearing the antennae, mandibles and maxillae appear to be represented by the head-shield or cephalite. The tergal element of the somite bearing the palpognath is usually suppressed; that of the toxicognath is sometimes of large size as in some Geophilomorpha (Himantarium), sometimes small as inScutigera,Lithobius,Craterostigmus, sometimes suppressed probably by fusion with the tergum of the first leg-bearing somite as in the Scolopendromorpha. The sternal plates of all the jaw-bearing somites have disappeared, except in the case of the somite of the toxicognath, where it may be vestigial. In the case of the somites bearing the walking legs the tergal and sternal elements are preserved without fusion with the corresponding plates of the preceding or succeeding somites, so that great flexibility of the body is retained. The only exception to this is presented byScutigera, where the terga corresponding to the somites bearing the fifteen pairs of legs are reduced by fusion and suppression to seven. The walking legs are articulated to the inferior portion of the pleural or lateral area of the somites close to the external margins of the sterna, which widely separate those of the left from those of the right side. Generally speaking the legs resemble each other, although as a rule they progressively increase in length towards the posterior end of the body. They consist typically of six segments, of which the basal is termed the coxa and the apical the tarsus. The tarsus is armed with a single terminal claw, and, except in the Geophilomorpha and a few genera of other orders, is divided by a mesial transverse joint into two segments, as is the case inScolopendraandLithobiusfor example. But in some of the longer-legged, swift-footed centipedes of the order Lithobiomorpha (e.g.Henicops,Cermalobius) the tarsi are further subdivided. The multiplication of sub-segments reaches its maximum inScutigera, where the tarsi are extremely long, slender, flexible and annulated. The legs of the last pair are directed backwards in a line parallel with the long axis of the body, so that their coxae, fused in some cases with the pleural sclerites (Scolopendra,Geophilus), or free and of large size (Scutigera,Lithobius), serve to protect the small genital and anal somites. They are often greatly modified. In the males of some species ofLithobiusone or more of the segments is inflated or furnished with tubercle-bearing, tactile bristles; in some Geophilomorpha the whole limb is thickened in the male sex. In most Scolopendromorpha the basal segment is armed beneath with spines or spikes (Dacetum,Scolopocryptops); sometimes the whole appendage is thickened and terminated by a sharp and serrate claw (Theatops,Plutonium). In these cases the legs act as weapons of defence and offence. In other cases (Newportia) the tarsi lose the claw, become many-jointed and act as feelers, while inAlipesthe terminal segments are flattened, leaf-like and furnished with a peculiar stridulating organ. The genital somite is always small and sometimes retractile within the somite bearing the last pair of legs. Its tergal plate is usually retained, but its sternal plate is generally suppressed. In females of the Lithobiomorpha and Scutigeromorpha the appendages of this somite—the gonopods—are jointed, forcipate and relatively well developed although small. In the females of the other orders they are greatly reduced or absent. In the males their development varies considerably. They are well developed inScutigera, where they form two pairs of digitiform sclerites, whereas in the Geophilomorpha they are reduced to a pair of very short, two-jointed limbs. The anal somite is always small and limbless. InCraterostigmusthe genital and anal somites are represented by a pair of elongate valves projecting between the legs of the last pair. The structure of the gonopods is unknown, and the homology between the two valves and the skeletal elements of the somites in question not clearly understood.Modified from Heymons,Bib. Zool., 1901, by permission of E. Nagele.Fig.1.A, Diagram of anterior extremity of an early embryo ofScolopendra, ventral view;cl, clypeus;lb, labrum;m, mouth;p.a, preantennal appendage;a, antenna;int, premandibular rudiment;mdl, mandible;mx, maxilla;p.g, palpognath;t.g, toxicognath;lg. 1, first pair of walking legs.B, Posterior end of a later embryo ofScolopendra, ventral view, showing the anal segment or telson (t); the legs of the last pair in the adult (lg.21) and the two rudimentary pairs of legs (lg.22,lg.23).A study of the development ofScolopendrahas shown that the antennae of the adult are the appendages of the second postoral metamere and the mandibles those of the fourth, the first postoral metamere, which has a pair of transient preantennal appendages, and the third, which has no appendages, being excalated at an early stage of embryonic growth. Furthermore, behind the legs of the last pair two pairs of appendages are present. The second of these persists as the gonopods of the adult, but the first is suppressed. Possibly, however, it is represented in the male ofScutigeraby the anterior branches of the gonopods. The cerebral or cephalic portion of the nervous system consists of a quadrilobate mass. From the two upper lobes, which are set transversely, arise the ocular nerves; from the two lower lobes, which are united by a transverse commissure, spring the antennal nerves in front and the chords which form the oesophageal collar behind. These chords unite below the oesophagus to form the compound suboesophageal ganglion, whence the nerves for the four pairs of jaws arise. The ventral system consists of a double chord uniting in each of the leg-bearing segments in a ganglionic swelling which gives off four pairs of nerves to the limbs and tissues of the somite. There is a single ganglion in the genital segment.Eyes are frequently absent. When present they may be either simple or compound,i.e.consisting externally of a single lens (monomeniscous) of or an aggregation of lenses (polymeniscous). Simple eyes vary in number on each side of the head from one, as inHenicops, to many as forty, as in some species ofLithobius. InScolopendra, where there are four, the corneal lens is a biconvex thickening of the cuticle. The soft or retinal portion of the eye beneath the lens consists of an aggregation of large cells forming a single layer continuous with the epidermic cells of the circumocular area. Thus the eye is monostichous. The arrangement of the cells, however, is peculiar. They are invaginated to form what may be described as a very deep cup with exceedingly thick walls and correspondingly narrow median space, the outer surface of the cup being formed by the inner or proximal ends of the cells and the inner surface by their outer or distal ends. It results from this arrangement that the cells forming all but the bottom of the invagination lie horizontally,i.e.at right angles to the vertical axis of the eye. From the distal ends of the cells are secreted chitinous rhabdomeres, forming a rhabdom which occupies and fills up the central portion of the cup beneath the middle of the corneal lens. The outer ends of the cells are nucleated and are continuous with the fibres of the optic nerve, which passes from the outer surface of the bottom of the cup to the brain. Compound eyes are found only in theScutigeridae. Externally the eye consists of one hundred or more little lenses or lenticles. The retinal portion is composed of a corresponding number of ocular units or ommatidia. Each ommatidium is an elongated cone with its broad extremity abutting against the corneal lenticle. It consists of a non-nucleated crystalline cone developed from embryonic cells, and is enveloped in three tiers of large nucleated cells. The cells of the outermost tier are heavily pigmented; those of the middle and innermost (proximal) tiers, the retinal cells, are at their inner extremities produced into threads continuous with the fibres of the optic nerve. In the space between these cells and the crystalline cone which they surround, there is a layer of rhabdomeres deposited apparently by the cells.A and B after Heymons,Bibl Zool, 1901, by permission of E. Nagele.A, Brain ofScolopendra.n. ant, Antennal nerves;n. opt, ocular nerves;n. pr. ant, preantennal nerves;oes. comm, oesophageal commissure.B, Section of Eye of Scolopendra.len, Corneal lens;ret, retinal or visual cells;n. opt, optic nerve.Fig. 2.C after Adensamer,Verh. z. b. Verein, Vienna, 1893, pl. vii.C, Ocular unit or ommatidium of compound Eye ofScutigera.len, corneal lenticle;c.c, crystalline cone;1, pigmented cells of outermost tier;2,3, retinular cells of middle and innermost tiers;rbd, rhabdomeres;n. opt, optic nerve;pg, pigment cells.Fig.3.—Diagram of Alimentary Canal ofLithobius.a, Anus.mgMid-Gut.hg, Hind-Gut.mt, Malphighian tubule.s.gl, Salivary gland.lg.1,lg.15, Legs of first and fifteenth pairs.The alimentary canal is a simple tube running without convolutions from the mouth to the anus. Its anterior portion or pharynx, which arises from the stomodaeal invagination in the embryo, is short; a pair of large, so-called salivary glands open into it. The mesenteric part of the canal is relatively wide and receives at its junction with the hind-gut the excretory products of a pair of very long and slender malpighian tubes of proctodaeal origin. The posterior end of the canal, arising from the proctodaeum, is relatively short and narrow.The generative organs vary in structural details in different centipedes. In the male ofLithobiusthe testes consist of a single coiled tube lying above the alimentary canal. The slender vas deferens which proceeds from its hinder end divides posteriorly into a right and left branch, embracing the gut and uniting beneath it to form a common chamber or atrium within the genital orifice. The atrium receives the secretion of two pairs of large accessory glands; and a pair of tubes, or vesiculae seminales, open, one on each side, into the divided sperm ducts close to their point of origin above the intestine. The organs of the female are very similar. There is a large median ovary followed by a short oviduct forming a circum-intestinal collar and a common atrium. Into the latter open a pair of short receptacula seminis and the slender duct of two pairs of large accessory glands. There is nothing in the female corresponding to the supra-intestinal vesiculae seminales of the male. In the male ofScolopendra, on the contrary, there are as many as twelve pairs of somewhat sausage-shaped testes, approximated two by two. From each pair proceed two slender ducts which open into a median duct coiled in the posterior third of the body and much expanded in the last three of the leg-bearing segments. The right and left portions of the intestinal ring of the genital duct are unequally developed, and there are no vesiculae seminales, but two pairs of accessory glands communicate with the genital atrium as inLithobius. In the femaleScolopendrathe right and left portions of the intestinal collar are also unequally developed, and only a single pair of accessory glands besides the receptacula seminis open into the atrium.After Heymons,Bibl. Zool, 1901, by permission of E. Nagele.Fig.4.—Posterior portion of generative organs of male ofScolopendra(A), of female (B).t, Testes;v.d, vas deferens;ov, ovary;r.s, receptaculum seminis;gl. acc, accessory glands;g.o, generative orifice.The heart is tubular and lies in the middle dorsal line immediatelybeneath the integument. It consists of a series of chambers corresponding roughly to the leg-bearing segments, and lies in a blood-sinus formed by a pericardial membrane whence large alary muscles extend to the sides of the body. Each chamber gives off inScolopendraa pair of fine lateral vessels, and is furnished at its posterior extremity with a pair of orifices by which the blood re-enters the organ from the pericardial space. From the anterior chamber, which lies in the first or second leg-bearing segment, proceed three arteries, a median which runs forwards into the head to supply the brain and other organs, and a lateral which with its fellow of the opposite side forms an oesophageal aortic collar. From the sides of the latter arise vessels to the gnathites, and from its inferior portion an unpaired vessel passes forwards into the head and another backwards above the nerve chord to the posterior end of the body, supplying each segment in its course with a delicate lateral branch. InScolopendrathe chambers of the heart, excepting the first and last, which are small, are subequal in size; but in forms likeScutigerawhere the terga are very unequal in size a corresponding inequality in the size of the chambers is manifested.A after Newport,Phil. Trans., 1843. B after Haase,Zool. Beitrage, i. pt. 65, 1884, by permission of J.N. Kern. C after Haase,loc. cit.A, Anterior extremity ofScolopendra, showing two chambers of the heart (h), the aortic ring (a), the alae cordis (a.m) and a cardiac orifice (o).B, Two segments ofScolopendra, showing the branching and anastomosing tracheae and a spiracle (sp).Fig 5.C, A pair of tufted tracheae ofScutigera. d, Dorsal plate; t.s, tracheal sac; tr, tracheal tubes.In all centipedes, exceptScutigera, respiration is effected by chitinized tracheal tubes which extend with their ramifications throughout the body and open to the exterior by means of spiracles perforating the lateral or pleural membrane of more or fewer of the somites below the edge of the terga. Spiracles are never present upon the anal, genital and last leg-bearing somites, and only rarely, as inHenicops, upon the somite bearing the legs of the first pair. In the majority of cases the spiracles are circular, sigmoid or slit-like orifices, with chitinized rim, leading into a pocket-like integumental infolding, from which emanate numerous small tracheal tubes which soon anastomose to form the main tracheal trunks. InDacetum, one of theScolopendridae, there is no pocket-like infolding, the small tracheal tubes opening direct to the exterior on a large subcircular plate where their apertures fuse to form a complicated network. The apertures, as in the case of other genera, are protected by fine hairs; and the tracheae themselves are strengthened by a fine spiral filament. In theLithobiidaethe tracheae do not anastomose; but inScolopendraandGeophilusthe main trunks in each segment fuse transversely with those of the opposite side and also longitudinally with those of the preceding and succeeding segments.InScutigerathe tracheae differ both in structure and position from those of all other Chilopoda. The spiracles, unpaired and seven in number, open in the median dorsal line. Each leads into a short sac from which five tracheal tubes depend into the pericardial blood-sinus.
Structure of the Chilopoda.—The exoskeletal elements of a typical somite consist of a dorsal plate or tergum, a ventral plate or sternum, a lateral or pleural membrane, often strengthened with chitinous sclerites, and a pair of appendages. At the anterior extremity there is a head-shield or cephalite, which bears eyes, when present, and a pair of antennae. In all centipedes, except theScutigeridae, the preantennal portion of the cephalite is sharply reflexed, ventrally forming an area called the clypeus. The inferior edge of this bears the labrum, which is usually represented by a small median, and two large lateral plates. The appendages are modified as a single pair of antennae, four pairs of jaws or gnathites, a variable number of walking legs and a single pair of generative limbs or gonopods. The antennae, articulated to the forepart of the head and preoral in position, are long and flexible and consist of fourteen or more segments. The jaws of the first pair of mandibles are stout and bi-segmented, with a dentate cutting edge. Those of the second pair or maxillae vary considerably in structure in different groups. They are foliaceous and are usually regarded as biramous. In some genera (Scutigera,Lithobius) the inner branch consists of two distinct segments meeting those of the opposite side in the middle line. The outer branch, which is always larger, consists of three or four segments. Generally, however, the basal segments of the two branches are coalesced with each other and with the corresponding segments of the opposite side to form a single broad transverse plate. The above described condition seen inScutigerasuggests that two pairs of jaws may be involved in the formation of the maxillae in the Chilopoda. The jaws of the third pair, the palpognaths or second pair of maxillae, resemble dwarfed walking legs, and consist of five or six segments, of which the basal or coxa is united mesially to its fellow. The jaws of the fourth pair, the toxicognaths or poison-jaws, are long and powerful, and consist like the legs primarily of six segments, whereof the basal is large and usually fused with its fellow to form a large coxal plate, the second is small and generally suppressed by fusion with the third, the fourth and fifth are also small, while the sixth is transformed into a great piercing fang, at the tip of which opens the duct of a poison gland lodged within the appendage.
The tergal elements of the somites bearing the antennae, mandibles and maxillae appear to be represented by the head-shield or cephalite. The tergal element of the somite bearing the palpognath is usually suppressed; that of the toxicognath is sometimes of large size as in some Geophilomorpha (Himantarium), sometimes small as inScutigera,Lithobius,Craterostigmus, sometimes suppressed probably by fusion with the tergum of the first leg-bearing somite as in the Scolopendromorpha. The sternal plates of all the jaw-bearing somites have disappeared, except in the case of the somite of the toxicognath, where it may be vestigial. In the case of the somites bearing the walking legs the tergal and sternal elements are preserved without fusion with the corresponding plates of the preceding or succeeding somites, so that great flexibility of the body is retained. The only exception to this is presented byScutigera, where the terga corresponding to the somites bearing the fifteen pairs of legs are reduced by fusion and suppression to seven. The walking legs are articulated to the inferior portion of the pleural or lateral area of the somites close to the external margins of the sterna, which widely separate those of the left from those of the right side. Generally speaking the legs resemble each other, although as a rule they progressively increase in length towards the posterior end of the body. They consist typically of six segments, of which the basal is termed the coxa and the apical the tarsus. The tarsus is armed with a single terminal claw, and, except in the Geophilomorpha and a few genera of other orders, is divided by a mesial transverse joint into two segments, as is the case inScolopendraandLithobiusfor example. But in some of the longer-legged, swift-footed centipedes of the order Lithobiomorpha (e.g.Henicops,Cermalobius) the tarsi are further subdivided. The multiplication of sub-segments reaches its maximum inScutigera, where the tarsi are extremely long, slender, flexible and annulated. The legs of the last pair are directed backwards in a line parallel with the long axis of the body, so that their coxae, fused in some cases with the pleural sclerites (Scolopendra,Geophilus), or free and of large size (Scutigera,Lithobius), serve to protect the small genital and anal somites. They are often greatly modified. In the males of some species ofLithobiusone or more of the segments is inflated or furnished with tubercle-bearing, tactile bristles; in some Geophilomorpha the whole limb is thickened in the male sex. In most Scolopendromorpha the basal segment is armed beneath with spines or spikes (Dacetum,Scolopocryptops); sometimes the whole appendage is thickened and terminated by a sharp and serrate claw (Theatops,Plutonium). In these cases the legs act as weapons of defence and offence. In other cases (Newportia) the tarsi lose the claw, become many-jointed and act as feelers, while inAlipesthe terminal segments are flattened, leaf-like and furnished with a peculiar stridulating organ. The genital somite is always small and sometimes retractile within the somite bearing the last pair of legs. Its tergal plate is usually retained, but its sternal plate is generally suppressed. In females of the Lithobiomorpha and Scutigeromorpha the appendages of this somite—the gonopods—are jointed, forcipate and relatively well developed although small. In the females of the other orders they are greatly reduced or absent. In the males their development varies considerably. They are well developed inScutigera, where they form two pairs of digitiform sclerites, whereas in the Geophilomorpha they are reduced to a pair of very short, two-jointed limbs. The anal somite is always small and limbless. InCraterostigmusthe genital and anal somites are represented by a pair of elongate valves projecting between the legs of the last pair. The structure of the gonopods is unknown, and the homology between the two valves and the skeletal elements of the somites in question not clearly understood.
A study of the development ofScolopendrahas shown that the antennae of the adult are the appendages of the second postoral metamere and the mandibles those of the fourth, the first postoral metamere, which has a pair of transient preantennal appendages, and the third, which has no appendages, being excalated at an early stage of embryonic growth. Furthermore, behind the legs of the last pair two pairs of appendages are present. The second of these persists as the gonopods of the adult, but the first is suppressed. Possibly, however, it is represented in the male ofScutigeraby the anterior branches of the gonopods. The cerebral or cephalic portion of the nervous system consists of a quadrilobate mass. From the two upper lobes, which are set transversely, arise the ocular nerves; from the two lower lobes, which are united by a transverse commissure, spring the antennal nerves in front and the chords which form the oesophageal collar behind. These chords unite below the oesophagus to form the compound suboesophageal ganglion, whence the nerves for the four pairs of jaws arise. The ventral system consists of a double chord uniting in each of the leg-bearing segments in a ganglionic swelling which gives off four pairs of nerves to the limbs and tissues of the somite. There is a single ganglion in the genital segment.
Eyes are frequently absent. When present they may be either simple or compound,i.e.consisting externally of a single lens (monomeniscous) of or an aggregation of lenses (polymeniscous). Simple eyes vary in number on each side of the head from one, as inHenicops, to many as forty, as in some species ofLithobius. InScolopendra, where there are four, the corneal lens is a biconvex thickening of the cuticle. The soft or retinal portion of the eye beneath the lens consists of an aggregation of large cells forming a single layer continuous with the epidermic cells of the circumocular area. Thus the eye is monostichous. The arrangement of the cells, however, is peculiar. They are invaginated to form what may be described as a very deep cup with exceedingly thick walls and correspondingly narrow median space, the outer surface of the cup being formed by the inner or proximal ends of the cells and the inner surface by their outer or distal ends. It results from this arrangement that the cells forming all but the bottom of the invagination lie horizontally,i.e.at right angles to the vertical axis of the eye. From the distal ends of the cells are secreted chitinous rhabdomeres, forming a rhabdom which occupies and fills up the central portion of the cup beneath the middle of the corneal lens. The outer ends of the cells are nucleated and are continuous with the fibres of the optic nerve, which passes from the outer surface of the bottom of the cup to the brain. Compound eyes are found only in theScutigeridae. Externally the eye consists of one hundred or more little lenses or lenticles. The retinal portion is composed of a corresponding number of ocular units or ommatidia. Each ommatidium is an elongated cone with its broad extremity abutting against the corneal lenticle. It consists of a non-nucleated crystalline cone developed from embryonic cells, and is enveloped in three tiers of large nucleated cells. The cells of the outermost tier are heavily pigmented; those of the middle and innermost (proximal) tiers, the retinal cells, are at their inner extremities produced into threads continuous with the fibres of the optic nerve. In the space between these cells and the crystalline cone which they surround, there is a layer of rhabdomeres deposited apparently by the cells.
a, Anus.
mgMid-Gut.
hg, Hind-Gut.
mt, Malphighian tubule.
s.gl, Salivary gland.
lg.1,lg.15, Legs of first and fifteenth pairs.
The alimentary canal is a simple tube running without convolutions from the mouth to the anus. Its anterior portion or pharynx, which arises from the stomodaeal invagination in the embryo, is short; a pair of large, so-called salivary glands open into it. The mesenteric part of the canal is relatively wide and receives at its junction with the hind-gut the excretory products of a pair of very long and slender malpighian tubes of proctodaeal origin. The posterior end of the canal, arising from the proctodaeum, is relatively short and narrow.
The generative organs vary in structural details in different centipedes. In the male ofLithobiusthe testes consist of a single coiled tube lying above the alimentary canal. The slender vas deferens which proceeds from its hinder end divides posteriorly into a right and left branch, embracing the gut and uniting beneath it to form a common chamber or atrium within the genital orifice. The atrium receives the secretion of two pairs of large accessory glands; and a pair of tubes, or vesiculae seminales, open, one on each side, into the divided sperm ducts close to their point of origin above the intestine. The organs of the female are very similar. There is a large median ovary followed by a short oviduct forming a circum-intestinal collar and a common atrium. Into the latter open a pair of short receptacula seminis and the slender duct of two pairs of large accessory glands. There is nothing in the female corresponding to the supra-intestinal vesiculae seminales of the male. In the male ofScolopendra, on the contrary, there are as many as twelve pairs of somewhat sausage-shaped testes, approximated two by two. From each pair proceed two slender ducts which open into a median duct coiled in the posterior third of the body and much expanded in the last three of the leg-bearing segments. The right and left portions of the intestinal ring of the genital duct are unequally developed, and there are no vesiculae seminales, but two pairs of accessory glands communicate with the genital atrium as inLithobius. In the femaleScolopendrathe right and left portions of the intestinal collar are also unequally developed, and only a single pair of accessory glands besides the receptacula seminis open into the atrium.
The heart is tubular and lies in the middle dorsal line immediatelybeneath the integument. It consists of a series of chambers corresponding roughly to the leg-bearing segments, and lies in a blood-sinus formed by a pericardial membrane whence large alary muscles extend to the sides of the body. Each chamber gives off inScolopendraa pair of fine lateral vessels, and is furnished at its posterior extremity with a pair of orifices by which the blood re-enters the organ from the pericardial space. From the anterior chamber, which lies in the first or second leg-bearing segment, proceed three arteries, a median which runs forwards into the head to supply the brain and other organs, and a lateral which with its fellow of the opposite side forms an oesophageal aortic collar. From the sides of the latter arise vessels to the gnathites, and from its inferior portion an unpaired vessel passes forwards into the head and another backwards above the nerve chord to the posterior end of the body, supplying each segment in its course with a delicate lateral branch. InScolopendrathe chambers of the heart, excepting the first and last, which are small, are subequal in size; but in forms likeScutigerawhere the terga are very unequal in size a corresponding inequality in the size of the chambers is manifested.
In all centipedes, exceptScutigera, respiration is effected by chitinized tracheal tubes which extend with their ramifications throughout the body and open to the exterior by means of spiracles perforating the lateral or pleural membrane of more or fewer of the somites below the edge of the terga. Spiracles are never present upon the anal, genital and last leg-bearing somites, and only rarely, as inHenicops, upon the somite bearing the legs of the first pair. In the majority of cases the spiracles are circular, sigmoid or slit-like orifices, with chitinized rim, leading into a pocket-like integumental infolding, from which emanate numerous small tracheal tubes which soon anastomose to form the main tracheal trunks. InDacetum, one of theScolopendridae, there is no pocket-like infolding, the small tracheal tubes opening direct to the exterior on a large subcircular plate where their apertures fuse to form a complicated network. The apertures, as in the case of other genera, are protected by fine hairs; and the tracheae themselves are strengthened by a fine spiral filament. In theLithobiidaethe tracheae do not anastomose; but inScolopendraandGeophilusthe main trunks in each segment fuse transversely with those of the opposite side and also longitudinally with those of the preceding and succeeding segments.
InScutigerathe tracheae differ both in structure and position from those of all other Chilopoda. The spiracles, unpaired and seven in number, open in the median dorsal line. Each leads into a short sac from which five tracheal tubes depend into the pericardial blood-sinus.
Existing Chilopoda may be classified as follows, into five orders referable to two subclasses—
Subclass 1, Pleurostigma.—Chilopods furnished with a rich system of branching tracheal tubes, the spiracles of which are paired and open upon the pleural area of more or fewer of the somites. Each leg-bearing somite contains a distinct tergum and sternum, the number of sterna never exceeding that of the terga. Eyes are either preserved or lost; when preserved they are represented either by a single one-lensed ocellus or by an aggregation of such ocelli on each side of the head. The anterior portion of the head, bearing the labrum, is bent sharply downwards and backwards beneath the larger posterior portion lying behind the antennae, so that these appendages, approximated in the middle line, project directly forwards from the margin of the head formed by this retroversion of the labral area. The maxillae are short and have no sensory organ; the palpognaths consist of four segments, and the toxicognaths have their basal segments fused to form a single coxal plate.
A, Upper view of anterior extremity inGeophilus.
a, Basal segments of antennae.
c, Cephalic plate.
t.palp, Tergal plate of somite, bearing palpognaths.
t.tox, Tergal plate of somite, bearing toxicognaths (tox).
t.lg.1, Tergal plate of somite, bearing legs of first pair.
B, Toxicognaths ofScolopendra, showing the large coxal plate and the reduced penultimate and antepenultimate segments.
C, Terminal segment or fang of the same, showing the orifice of the poison gland.
(After Latzel,Die Myr. öst.-ung. Mon.vol. i. “Chilopoda,” Vienna, 1880.)
Order 1. Geophilomorpha.—Chilopods with a large and indefinite number of somites, most of which are partially or completely divided into a smaller anterior segment, represented by a pretergal and two presternal sclerites, and a larger posterior segment bearing the spiracles and legs. Spiracles are present upon all the leg-bearing somites except the first and last; and the legs which are short and subequal in length consist of six segments, the basal of which remains small. There are no eyes, and the antennae consist invariably of fourteen segments. The tergal plate of the somite bearing the toxicognaths always remains distinct and separates the head-shield from the tergum of the first leg-bearing somite. The penultimate and antepenultimate segments of the toxicognaths are reduced on the preaxial side of the appendage to the condition of arthrodial integumental folds and suppressed on the postaxial side where the distal segment or fang is firmly jointed to the femoral segment. In the last leg-bearing somite the pleural sclerites coalesce with the coxa of the appendage; but the second segment (trochanter) of this appendage does not fuse with the third (femur). The genital and anal somites are not retractile within the last leg-bearing somite, and the gonopods typically persist in the male as small two-jointed appendages and in the female as jointed or unjointed sclerites. The young are hatched with the full number of segments.Remarks.—The Geophilomorpha are universally distributed in suitable localities. The number of families into which the order should be divided is as yet unsettled, some authors admitting several groups of this rank, others referring all the genera to a single family,Geophilidae. In habits theGeophilidaeare mostly subterranean, living in the earth and feeding principally upon earthworms. Occasionally they may be found eating fruit or fungi, probably for the sake of moisture. Although without eyes, they are extremely sensitive to light, and when exposed to it crawl away in serpentine fashion to the nearest sheltered spot, feeling the way with their antennae. Theycan, however, progress with almost equal facility backwards, using the legs of the posterior pair as feelers. Differing from the majority of the family in habits are the two speciesLinotaenia maritimaandSchendyla submarina, which live under stones or seaweed between tide-marks on the coasts of western Europe. Most, if not all, the species are provided with glands, which open upon the sterna and secrete a fluid which in some forms (Himantarium) is blood-red, while in others it is phosphorescent. In the tropical formOrphnaeus phosphoreusthe fluid is known to possess this property; and its luminosity has been repeatedly observed in England in the autumn in the case ofLinotaenia acuminataandL. crassipes.The number of pairs of legs within this family varies from between thirty and forty to over one hundred and seventy. Corresponding discrepancies are observable in size, the smallest specimens being less than 1 in. long and barely 1 mm. wide, while the largest example recorded, a specimen ofNotiphilidesfrom Venezuela, was 11 in. long and1⁄3of an inch wide.Fig.7.—Scolopendra morsitans(after Buffon).A,a, Cephalic plate.b, Tergum of segment, bearing first pair of legs (d).c, Tip of palpognath.e, Antenna.f, Toxicognath.g, Last pair of appendages, enlarged and directed backwards.When pairing takes place the female fertilizes herself by taking up a spermatophore which a male has left upon a sheet of web for that purpose. The female lays a cluster of eggs in some sheltered spot, sometimes in a specially prepared nest, and encircling them with her body, keeps guard until the young disperse and shift for themselves.Order 2. Scolopendromorpha.—Chilopods differing principally from the Geophilomorpha in that the number of leg-bearing somites is definitely fixed at twenty-three or twenty-one. These are differentiated into larger and smaller, which alternate with nearly complete regularity. The anterior portion of each somite is only partially cut off as a subsegment. The tergal plate of the somite bearing the toxicognaths is suppressed, probably by fusion with the tergum of the first leg-bearing somite. The antennae consist of a number of segments varying from seventeen to about thirty, and usually differing in the individuals of a species. The second segment (trochanter) of the legs of the last pair is coalesced with the third (femur). In only one genus, namelyPlutonium, which occurs in Italy, is there a pair of spiracles for each leg-bearing segment, except the first and last, as in the Geophilomorpha. In most genera there are only nine pairs of spiracles situated upon the 3rd, 5th, 8th, 10th, 12th, 14th, 16th, 18th and 20th leg-bearing segments, as inScolopendra,Cormocephalus,Cryptops, &c. In genera with twenty-three pairs of legs, likeScolopocryptops, there is an additional pair of spiracles on the twenty-second pedigerous segment; and a few genera such asRhysida, Edentistoma, possess a pair upon the 7th segment. Eyes, when present, are always four in number on each side. The newly hatched young has the full complement of appendages.This order is divided into four families:—Scolopendridae(Scolopendra,Rhysida),Cryptopidae(Cryptops,Theatops),Scolopocryptopidae(Scolopocryptops,Otocryptops) andNewportudae(Newportia). Apart from the frigid zones it is cosmopolitan in distribution, though only one genus (Cryptops) extends into north temperate latitudes. In the tropics and warmer countries of the southern hemisphere the genera and species are particularly abundant, and individuals reach the greatest dimensions, some specimens of the tropical American speciesScolopendra giganteaexceeding 12 in. in length. They are strictly carnivorous, their diet consisting of any animal, vertebrate or invertebrate, small enough to be overcome. They live in damp obscure places, under logs of wood or stones, and are nocturnal, shunning, like theGeophilidae, exposure to light; and as in theGeophilidae, the females guard their eggs and young until the latter disperse to lead an independent life.Order 3. Craterostigmomorpha.—Chilopods with twenty-one tergal plates as in the typical genera of Scolopendromorpha, but with only fifteen pairs of legs as in the Lithobiomorpha. As in some members of the latter order there is a single ocellus on each side of the head, the penultimate and antepenultimate segments of the toxicognaths are complete on the postaxial side of the appendage, and spiracles are present upon the 3rd, 5th, 8th, 10th, 12th and 14th leg-bearing somites. In the size and shape of the head, of the toxicognaths, of the tergal plate of this somite, and of the first leg-bearing somite, great similarity to some genera of Geophilomorpha (e.g. Mecistocephalus) is presented; but in the structure of the posterior end of the body this order differs from all the other orders of Chilopoda. The skeletal elements of the last leg-bearing segment are welded together to form a subcylindrical tube, and the genital and anal somites are represented by a pair of chitinous valves capable of opening below for the escape of the genital and intestinal products.After Pocock.Q.J.M.S.vol. 45, pl. 23, 1902.Fig.8.A, Anterior end ofCraterostigmusfrom above.a, Basal segments of antennae.c, Cephalic plate with eyes (o).t.tox, Tergal plate of somite bearing toxicognaths (tox).t.lg.1, Tergal plate of somite bearing legs of the first pair.B, Maxillae.C, Palpognath.D, Toxicognath.E, Last segment with genital capsule (g.c), and basal segments of legs of 14th and 15th pairs (lg. 14,lg. 15).This order, containing the familyCraterostigmidae, is based upon a remarkable genus and speciesCraterostigmus tasmanianus, of which only two specimens are known. These were collected under stones upon the summit of Mount Rumney in Tasmania. They are about 1½ in. in length; but nothing has been recorded of their habits. The chief morphological interest attaching toCraterostigmusis that, apart from certain structural peculiarities of its own, it presents features previously believed to be found exclusively either in the Scolopendromorpha, or the Geophilomorpha, or the Lithobiomorpha; and it shows how the Lithobiomorpha may be derived from a Scolopendromorphous type most nearly resemblingPlutoniumby the excalation of the third, sixth, ninth, eleventh, fourteenth and seventeenth leg-bearing somites.Order 4. Lithobiomorpha.Chilopoda with fifteen pairs of leg-bearing somites differentiated into larger and smaller, the 1st, 3rd, 5th, 7th, 8th, 10th, 12th and 14th being large, the others small. Spiracles present upon all the larger with the exception sometimes of the 1st. The toxicognaths are relatively weaker than in the orders hitherto considered, and have their basal segments less firmly fused mesially. In correlation with their weaker muscularity the first leg-bearing segment is relatively small. The gonopods, present and usually jointed in both sexes, are especially well developed and forcipate in the female, and arise from a large ventral plate resulting from the fusion of their coxae with the sternum of the genital somite. The antennae are many-jointed, and there is a single ocellus or a cluster of ocelli on each side of the head. The coxae of the legs are large, and those of the last four or five pairs usually contain glands opening by large orifices. The newly-hatched young has only seven pairs of legs, the remaining pairs being successively added as growth proceeds.The genera of this order are divisible into three families, theLithobiidae(Lithobius, Bothropolys),Henicopidae(Henicops, Haasiella), theCermatobiidae(Cermatobius).Cermatobius, based upon a single species,martensii, from the isl. of Adenara, is of peculiar interest, since in the absence of coxal pores, and the length and multi-articulation of the antennae and tarsal segments, it approaches more nearly toScutigerathan does any other pleurostigmous Chilopod. It is also stated that the spiracles have assumed a more dorsal position, thus foreshadowing the completely dorsal situation they have taken up in the Notostigma. TheHenicopidae, containing centipedes of small size, attains its maximum of development in the southern continents and islands, more particularly Australia, New Zealand, South Africa and South America. One genus (Lamyctes) however, occurs in Europe. TheLithobiidae, on the contrary, are almost exclusively northern in range, being particularly abundant and of large size individually in Europe, extra-tropical Asia, and North and Central America. In habits theLithobiidaeclosely resemble theScolopendridae. They are, however, comparatively far more agile with their shorter, more compact bodies and stronger legs. They are mostly of small size, the largest species,Lithobius fusciatus, of south Europe measuring only 2 in. in length of body. The females do not guard their eggs, but coat them with soil and leave them to their fate.
Order 1. Geophilomorpha.—Chilopods with a large and indefinite number of somites, most of which are partially or completely divided into a smaller anterior segment, represented by a pretergal and two presternal sclerites, and a larger posterior segment bearing the spiracles and legs. Spiracles are present upon all the leg-bearing somites except the first and last; and the legs which are short and subequal in length consist of six segments, the basal of which remains small. There are no eyes, and the antennae consist invariably of fourteen segments. The tergal plate of the somite bearing the toxicognaths always remains distinct and separates the head-shield from the tergum of the first leg-bearing somite. The penultimate and antepenultimate segments of the toxicognaths are reduced on the preaxial side of the appendage to the condition of arthrodial integumental folds and suppressed on the postaxial side where the distal segment or fang is firmly jointed to the femoral segment. In the last leg-bearing somite the pleural sclerites coalesce with the coxa of the appendage; but the second segment (trochanter) of this appendage does not fuse with the third (femur). The genital and anal somites are not retractile within the last leg-bearing somite, and the gonopods typically persist in the male as small two-jointed appendages and in the female as jointed or unjointed sclerites. The young are hatched with the full number of segments.
Remarks.—The Geophilomorpha are universally distributed in suitable localities. The number of families into which the order should be divided is as yet unsettled, some authors admitting several groups of this rank, others referring all the genera to a single family,Geophilidae. In habits theGeophilidaeare mostly subterranean, living in the earth and feeding principally upon earthworms. Occasionally they may be found eating fruit or fungi, probably for the sake of moisture. Although without eyes, they are extremely sensitive to light, and when exposed to it crawl away in serpentine fashion to the nearest sheltered spot, feeling the way with their antennae. Theycan, however, progress with almost equal facility backwards, using the legs of the posterior pair as feelers. Differing from the majority of the family in habits are the two speciesLinotaenia maritimaandSchendyla submarina, which live under stones or seaweed between tide-marks on the coasts of western Europe. Most, if not all, the species are provided with glands, which open upon the sterna and secrete a fluid which in some forms (Himantarium) is blood-red, while in others it is phosphorescent. In the tropical formOrphnaeus phosphoreusthe fluid is known to possess this property; and its luminosity has been repeatedly observed in England in the autumn in the case ofLinotaenia acuminataandL. crassipes.
The number of pairs of legs within this family varies from between thirty and forty to over one hundred and seventy. Corresponding discrepancies are observable in size, the smallest specimens being less than 1 in. long and barely 1 mm. wide, while the largest example recorded, a specimen ofNotiphilidesfrom Venezuela, was 11 in. long and1⁄3of an inch wide.
Fig.7.—Scolopendra morsitans(after Buffon).
A,a, Cephalic plate.
b, Tergum of segment, bearing first pair of legs (d).
c, Tip of palpognath.
e, Antenna.
f, Toxicognath.
g, Last pair of appendages, enlarged and directed backwards.
When pairing takes place the female fertilizes herself by taking up a spermatophore which a male has left upon a sheet of web for that purpose. The female lays a cluster of eggs in some sheltered spot, sometimes in a specially prepared nest, and encircling them with her body, keeps guard until the young disperse and shift for themselves.
Order 2. Scolopendromorpha.—Chilopods differing principally from the Geophilomorpha in that the number of leg-bearing somites is definitely fixed at twenty-three or twenty-one. These are differentiated into larger and smaller, which alternate with nearly complete regularity. The anterior portion of each somite is only partially cut off as a subsegment. The tergal plate of the somite bearing the toxicognaths is suppressed, probably by fusion with the tergum of the first leg-bearing somite. The antennae consist of a number of segments varying from seventeen to about thirty, and usually differing in the individuals of a species. The second segment (trochanter) of the legs of the last pair is coalesced with the third (femur). In only one genus, namelyPlutonium, which occurs in Italy, is there a pair of spiracles for each leg-bearing segment, except the first and last, as in the Geophilomorpha. In most genera there are only nine pairs of spiracles situated upon the 3rd, 5th, 8th, 10th, 12th, 14th, 16th, 18th and 20th leg-bearing segments, as inScolopendra,Cormocephalus,Cryptops, &c. In genera with twenty-three pairs of legs, likeScolopocryptops, there is an additional pair of spiracles on the twenty-second pedigerous segment; and a few genera such asRhysida, Edentistoma, possess a pair upon the 7th segment. Eyes, when present, are always four in number on each side. The newly hatched young has the full complement of appendages.
This order is divided into four families:—Scolopendridae(Scolopendra,Rhysida),Cryptopidae(Cryptops,Theatops),Scolopocryptopidae(Scolopocryptops,Otocryptops) andNewportudae(Newportia). Apart from the frigid zones it is cosmopolitan in distribution, though only one genus (Cryptops) extends into north temperate latitudes. In the tropics and warmer countries of the southern hemisphere the genera and species are particularly abundant, and individuals reach the greatest dimensions, some specimens of the tropical American speciesScolopendra giganteaexceeding 12 in. in length. They are strictly carnivorous, their diet consisting of any animal, vertebrate or invertebrate, small enough to be overcome. They live in damp obscure places, under logs of wood or stones, and are nocturnal, shunning, like theGeophilidae, exposure to light; and as in theGeophilidae, the females guard their eggs and young until the latter disperse to lead an independent life.
Order 3. Craterostigmomorpha.—Chilopods with twenty-one tergal plates as in the typical genera of Scolopendromorpha, but with only fifteen pairs of legs as in the Lithobiomorpha. As in some members of the latter order there is a single ocellus on each side of the head, the penultimate and antepenultimate segments of the toxicognaths are complete on the postaxial side of the appendage, and spiracles are present upon the 3rd, 5th, 8th, 10th, 12th and 14th leg-bearing somites. In the size and shape of the head, of the toxicognaths, of the tergal plate of this somite, and of the first leg-bearing somite, great similarity to some genera of Geophilomorpha (e.g. Mecistocephalus) is presented; but in the structure of the posterior end of the body this order differs from all the other orders of Chilopoda. The skeletal elements of the last leg-bearing segment are welded together to form a subcylindrical tube, and the genital and anal somites are represented by a pair of chitinous valves capable of opening below for the escape of the genital and intestinal products.
A, Anterior end ofCraterostigmusfrom above.
a, Basal segments of antennae.
c, Cephalic plate with eyes (o).
t.tox, Tergal plate of somite bearing toxicognaths (tox).
t.lg.1, Tergal plate of somite bearing legs of the first pair.
B, Maxillae.
C, Palpognath.
D, Toxicognath.
E, Last segment with genital capsule (g.c), and basal segments of legs of 14th and 15th pairs (lg. 14,lg. 15).
This order, containing the familyCraterostigmidae, is based upon a remarkable genus and speciesCraterostigmus tasmanianus, of which only two specimens are known. These were collected under stones upon the summit of Mount Rumney in Tasmania. They are about 1½ in. in length; but nothing has been recorded of their habits. The chief morphological interest attaching toCraterostigmusis that, apart from certain structural peculiarities of its own, it presents features previously believed to be found exclusively either in the Scolopendromorpha, or the Geophilomorpha, or the Lithobiomorpha; and it shows how the Lithobiomorpha may be derived from a Scolopendromorphous type most nearly resemblingPlutoniumby the excalation of the third, sixth, ninth, eleventh, fourteenth and seventeenth leg-bearing somites.
Order 4. Lithobiomorpha.Chilopoda with fifteen pairs of leg-bearing somites differentiated into larger and smaller, the 1st, 3rd, 5th, 7th, 8th, 10th, 12th and 14th being large, the others small. Spiracles present upon all the larger with the exception sometimes of the 1st. The toxicognaths are relatively weaker than in the orders hitherto considered, and have their basal segments less firmly fused mesially. In correlation with their weaker muscularity the first leg-bearing segment is relatively small. The gonopods, present and usually jointed in both sexes, are especially well developed and forcipate in the female, and arise from a large ventral plate resulting from the fusion of their coxae with the sternum of the genital somite. The antennae are many-jointed, and there is a single ocellus or a cluster of ocelli on each side of the head. The coxae of the legs are large, and those of the last four or five pairs usually contain glands opening by large orifices. The newly-hatched young has only seven pairs of legs, the remaining pairs being successively added as growth proceeds.
The genera of this order are divisible into three families, theLithobiidae(Lithobius, Bothropolys),Henicopidae(Henicops, Haasiella), theCermatobiidae(Cermatobius).Cermatobius, based upon a single species,martensii, from the isl. of Adenara, is of peculiar interest, since in the absence of coxal pores, and the length and multi-articulation of the antennae and tarsal segments, it approaches more nearly toScutigerathan does any other pleurostigmous Chilopod. It is also stated that the spiracles have assumed a more dorsal position, thus foreshadowing the completely dorsal situation they have taken up in the Notostigma. TheHenicopidae, containing centipedes of small size, attains its maximum of development in the southern continents and islands, more particularly Australia, New Zealand, South Africa and South America. One genus (Lamyctes) however, occurs in Europe. TheLithobiidae, on the contrary, are almost exclusively northern in range, being particularly abundant and of large size individually in Europe, extra-tropical Asia, and North and Central America. In habits theLithobiidaeclosely resemble theScolopendridae. They are, however, comparatively far more agile with their shorter, more compact bodies and stronger legs. They are mostly of small size, the largest species,Lithobius fusciatus, of south Europe measuring only 2 in. in length of body. The females do not guard their eggs, but coat them with soil and leave them to their fate.
Fig.9.—A,Scutigera rubrolineata(after Buffon). B, Tergum and part of a second of the same enlarged to show the position of the stigmatao, o; p, hinder margin of tergum.
After Latzel,Die Myr öst-ung. Mon.vol. i. “Chilopoda,” Vienna, 1880.
Fig.10.—Gnathites ofScutigera.
I. Mandibles.
II. Maxillae.
III. Palpognaths.
IV. Toxicognaths.
Subclass 2, Notostigma.—Chilopods with a series of mediandorsal tracheal sacs furnished with tubes dipping into the pericardial blood space, and opening each by an unpaired spiracle upon the 1st, 3rd, 5th, 8th, 10th, 12th and 14th leg-bearing somites. This characteristic is accompanied by the complete disappearance of the tergum of the 7th, either by fusion with that of the 8th or by excalation, and by the evanescence of the terga of the 2nd, 4th, 6th, 9th, 11th and 13th pedigerous somites. The preantennal area of the head is not strongly reflexed inferiorly, and the eyes are large and compound. The maxillae are long and have a sensory organ, the palpognaths are long, spiny and composed of five segments, like the primitive Chilopod leg, and the toxicognaths have their basal segments disunited and independently movable. Gonopods duplicated in the male.