Modern census-taking seems to have originated in the United States.
Professor von Mayr declares in a recent and authoritative work, "It was
no European state, but the United States of America that made a
beginning of census-taking in the large and true sense of that word,"
and Professor H. Wagner, writing of the censuses of Sweden, said to have
been taken in the 18th century, uses these words, "Since 1749 careful
parish registers have been kept by the clergy and have in general the
value of censuses." The same authority, although mentioning a reported
census of Norway in 1769, indicates his conviction that the first real
census of that country was in 1815. Sweden, Norway and the United States
are the only countries with any claim to have taken the first modern
census, as distinguished from a register of tax-payers, &c., the lineal
descendant of the old Roman census, and the innovation seems to be due
to the United States. If so, the first modern census was the American
census of 1790. At the present date more than three-fifths of the
estimated population of the world has been enumerated in this way. It is
of interest accordingly to note how and why the device originated.
The Federal census, which began in 1790 and has been taken every ten
years since under a mandate contained in the Constitution of the United
States, was the outgrowth of a controversy in the convention which
prepared the document. Representatives of the smaller states as a rule
claimed that the vote, and so the influence, of the states in the
proposed government should be equal. Representatives of the larger
states as a rule claimed that their greater population and wealth were
entitled to recognition. The controversy ended in the creation of a
bicameral legislature in the lower branch of which the claim of the
larger states found recognition, while in the upper, the Senate, each
state had two votes. In the House of Representatives seats were to be
distributed in proportion to the population, and the convention,
foreseeing rapid changes of population, ordained an enumeration of the
inhabitants and a redistribution or reapportionment of seats in the
House of Representatives every ten years.
The provision of the Constitution on the subject is as
follows:--"Representatives and direct taxes shall be apportioned among
the several states which may be included within this Union according to
their respective numbers, which shall be determined by adding to the
whole number of free persons, including those bound to service for a
term of years and excluding Indians not taxed, three-fifths of all other
persons. The actual enumeration shall be made within three years after
the first meeting of the Congress of the United States, and within every
subsequent term of ten years, in such manner as they shall by law
direct."
In 1790 the population was reported classed as slaves and free, the free
classed as white and others, the free whites as males and females, and
the free white males as under or above sixteen years of age. In 1800
and 1810 the same classification was preserved, except that five
age-groups instead of two were given for free white males and the same
five were applied also to free white females. In connexion with the
census of 1810 an attempt, perhaps the earliest in any country, was made
to gather certain industrial statistics showing "the number, nature,
extent, situation and value of the arts and manufactures of the United
States." In 1820 a sixth age class was introduced for free white males,
an age classification of four periods was applied to the free coloured
and the slaves of each sex, and the number of aliens and of persons
engaged in agriculture, in manufactures and in commerce was called for.
The inquiry into industrial statistics begun in 1810 was also repeated
and extended.
In 1830 thirteen age classes were employed for free whites of each sex,
and six for the free coloured and the slaves of each sex. The number of
aliens, of the deaf and dumb and the blind were also gathered.
The law under which the census of 1840 was taken contained a novel
provision for the preparation in connexion with the census of
statistical tables giving "such information in relation to mines,
agriculture, commerce, manufactures and schools as will exhibit a full
view of the pursuits, industry, education and resources of the country."
This was about the first indication of a tendency, which grew in
strength for half a century, to load the Federal census with inquiries
having no essential or necessary connexion with its main purpose, which
was to secure an accurate enumeration of the population as a basis for a
reapportionment of seats in the House of Representatives. This tendency
was largely due to a doubt whether the Federal government under the
Constitution possessed the power to initiate general statistical
inquiries, a doubt well expressed in the 9th edition of the
_Encyclopaedia Britannica_ by Francis A. Walker, himself a prominent
member of the party whose contention he states:--
"The reservation by the states of all rights not granted to the
general government makes it fairly a matter of question whether purely
statistical inquiries, other than for the single purpose of
apportioning representation, could be initiated by any other authority
than that of the states themselves. That large party which advocates a
strict and jealous construction of the constitution would certainly
oppose any independent legislation by the national Congress for
providing a registration of births, marriages and deaths, or for
obtaining social and industrial statistics, whether for the
satisfaction of the publicist or for the guidance of the legislature.
Even though the supreme court should decide such legislation to be
within the grant of powers to the general government, the distrust and
opposition, on constitutional grounds, of so large a portion of the
people, could not but go far to defeat the object sought."
The difficulty stated in the foregoing quotation, although now mainly of
historic importance, exerted great influence upon the development of the
American census prior to 1900.
The pioneer work of the census of 1840 in the fields of educational
statistics, statistics of occupations, of defective classes and of
causes of death, suffered from numerous errors and defects. Public
discussion of them contributed to secure radical modifications of scope
and method at the census of 1850. Before the census law was passed, a
census board, consisting of three members of the president's cabinet,
was appointed to draft plans for the inquiry, and the essential features
of its report prepared after consultation with a number of leading
statisticians were embodied in the law.
The census of 1850 was taken on six schedules, one for free inhabitants,
one for slaves, one for deaths during the preceding year, one for
agriculture, one for manufactures and one for social statistics. The
last asked for returns regarding valuation, taxation, educational and
religious statistics, pauperism, crime and the prevailing rates of wages
in each municipal division. It was also the first American census to
give a line of the schedule to each person, death or establishment
enumerated, and thus to make the returns in the individual form
indispensable for a detailed classification and compilation. The results
of this census were tabulated with care and skill, and a preliminary
analysis gave the salient results and in some cases compared them with
European figures.
The census of 1860 followed the model of its predecessor with slight
changes. When the time for the next census approached it was felt that
new legislation was needed, and a committee of the House of
Representatives, with James A. Garfield, afterwards president of the
United States, at its head, made a careful and thorough study of the
situation and reported an excellent bill, which passed the House, but
was defeated by untoward influences in the Senate. In consequence the
census of 1870 was taken with the outgrown machinery established twenty
years earlier, a law characterized by Francis A. Walker, the
superintendent of the census, who administered it, as "clumsy,
antiquated and barbarous." It suffered also from the fact that large
parts of the country had not recovered from the ruin wrought by four
years of civil war. In consequence this census marks the lowest ebb of
American census work. Tie accuracy of the results is generally denied by
competent experts. The serious errors were errors of omission, were
probably confined in the main to the Southern states, and were
especially frequent among the negroes.
Since 1870 the development of census work in the United States has been
steady and rapid. The law, which had been prepared for the census of
1870 by the House committee, furnished a basis for greatly improved
legislation in 1879, under which the tenth census was taken. By this law
the census office for the first time was allowed to call into existence
and to control an adequate local staff of supervisors and enumerators.
The scope of the work was so extended as to make the twenty-two quarto
volumes of the tenth census almost an encyclopaedia, not only of the
population, but also of the products and resources of the United States.
Probably no other census in the world has ever covered so wide a range
of subjects, and perhaps none except that of India and the eleventh
American census has extended through so many volumes. The topics usually
contained in a census suffered from the great addition of other and less
pertinent matter, and the reputation of the work was unfavourably
affected by the length of time required to prepare and publish the
volumes (the last ones not appearing until near the end of the decade),
the original underestimate of the cost of the work, which made frequent
supplementary appropriations necessary, the resignation of the
superintendent, Francis A. Walker, in 1882, and the disability and death
of his successor, Charles W. Seaton. The eleventh census was taken under
a law almost identical with that of the tenth, and extended through
twenty-five large volumes, presenting a work almost as encyclopaedic,
but much more distinctively statistical.
The popular opinion of a census, at least in the United States, depends
largely upon the degree to which its figures for the population of the
country, of states, and especially of cities, meet or fail to meet the
expectations of the interested public. Judged by this standard, the
census of 1890 was less favourably received than that of 1880. The
enumerated population of the country in 1880 was larger than had been
anticipated; and in the face of these figures it was difficult for local
complaints, even where they were made, to find hearing and acceptance.
But according to the eleventh census the decennial rate of growth of
population fell suddenly from over 30%, which the figures had shown
between 1870 and 1880, and in every preceding decade of the century,
except that of the Civil War, to less than 25%, in spite of an
immigration nearly double that of any preceding decade. For this change
no adequate explanation was offered by the census office. Hence the
protests of those who believed that the figures for population were too
small swelled into a general chorus of dissatisfaction. But the census
was probably more correct than the critics. Most of the motives
influencing popular estimates of population in the United States tend to
exaggeration. The convention which drafted the Constitution of the
United States attempted to secure a balance of interests by apportioning
both representatives in Congress and direct taxes according to
population. A passage in _The Federalist_ suggests the motives of the
convention as follows:--
"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 the amount
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.
+------+---------------------+------+-----------------------+
| | Cost. | | Cost. |
| +----------+----------+ +------------+----------+
| Date.| Total in |Per Capita| Date.| Total in |Per Capita|
| | dollars. |in cents. | | dollars. |in cents. |
+------+----------+----------+------+------------+----------+
| 1790 | 44,377 | 1.12 | 1850 | 1,423,351 | 6.13 |
| 1800 | 66,109 | 1.24 | 1860 | 1,969,377 | 6.26 |
| 1810 | 178,445 | 2.46 | 1870 | 3,421,198 | 8.87 |
| 1820 | 208,526 | 2.16 | 1880 | 5,790,678 | 11.48 |
| 1830 | 378,545 | 2.94 | 1890 | 11,547,127 | 18.33 |
| 1840 | 833,371 | 4.88 | 1900 | 16,116,930 | 21.16 |
+------+----------+----------+------+------------+----------+
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 represented by
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. nigra_ is
knapweed, common in meadows and pastureland; _C. Cyanus_ is the
bluebottle or cornflower, a well-known cornfield weed; _C. Calcitrapa_
is 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; and _C.
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) from [Greek: kentein] (goad) and [Greek: tauros] (bull),
implying a people who were primarily herdsmen, (2) from [Greek: kentein]
and the common termination [Greek: -auros] or [Greek: -aura] ("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's
_Lexikon der Mythologie_). Fig. 34 in article GREEK 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 century B.C.) and Aratus (3rd
century B.C.), Ptolemy catalogued thirty-seven stars in it.
_[alpha]-Centauri_ is 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;
_[omega]-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, from
_centeni_, distributive of _centum_, 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_, from _centum_, and _annus_, 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 of _Scolopendra_, 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 the
_Scutigeridae_, 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 in _Scutigera_ suggests 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 in
_Scutigera_, _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 by _Scutigera_, 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 in _Scolopendra_ and _Lithobius_ for
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 in _Scutigera_, 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 of
_Lithobius_ one 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 in _Alipes_ the 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 in _Scutigera_, 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. In _Craterostigmus_ the 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 of _Scolopendra_ has 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 of _Scutigera_ by 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.
[Illustration: Modified from Heymons, _Bib. Zool._, 1901, by
permission of E. Nagele.