aquatic relations. The front of the head is not in contact with the
haunches of the fore-legs. There is usually a marked difference
between the wings of the two pairs. The fore-wing is generally divided
into a firm coriaceous basal region, occupying most of the area, and a
membranous terminal portion, while the hind-wing is delicate and
entirely membranous (see fig. 6). In the firm portion of the fore-wing
two distinct regions can usually be distinguished; most of the area is
formed by the _corium_ (fig. 6, co), which is separated by a
longitudinal suture from the _clavus_ (fig. 6, cl) on its hinder edge,
and in some families there is also a _cuneus_ (fig. 9 cu) external to
and an _embolium_ in front of the _corium_.
[Illustration: After Marlatt, _Bull._ 4 (N.S.) _Div. Ent. U.S. Dept.
Agr._
FIG. 8.--Bed-bug (_Cimex lectularius_, Linn.).
a, Female from above;
b, From beneath;
c, Vestigial wing;
d, Jaws, very highly magnified (tips of mandibles and 1st maxillae
still more highly magnified).]
Most Heteroptera are flattened in form, and the wings lie flat, or
nearly so, when closed. The young Heteropteron is hatched from the egg
in a form not markedly different from that of its parent; it is active
and takes food through all the stages of its growth. It is usual to
divide the Heteroptera into two tribes--the Gymnocerata and the
Cryptocerata.
_Gymnocerata._--This tribe includes some eighteen families of
terrestrial, arboreal and marsh-haunting bugs, as well as those
aquatic Heteroptera that live on the surface-film of water. The
feelers are elongate and conspicuous. The _Pentatomidae_
(shield-bugs), some of which are metallic or otherwise brightly
coloured, are easily recognized by the great development of the
scutellum, which reaches at least half-way back towards the tip of the
abdomen, and in some genera covers the whole of the hind body, and
also the wings when these are closed. The _Coreidae_ have a smaller
scutellum, and the feelers are inserted high on the head, while in the
_Lygaeidae_ they are inserted lower down. These three families have
the foot with three segments. In the curious little _Tingidae_, whose
integuments exhibit a pattern of network-like ridges, the feet are
two-segmented and the scutellum is hidden by the pronotum. The
_Aradidae_ have two segmented feet, and a large visible scutellum. The
_Hydrometridae_ are a large family including the pond-skaters and
other dwellers on the surface-film of fresh water, as well as the
remarkable oceanic genus _Halobates_ already referred to. The
_Reduviidae_ are a family of predaceous bugs that attack other
insects and suck their juices; the beak is short, and carried under
the head in a hook-like curve, not--as in the preceding
families--lying close against the breast. The _Cimicidae_ have the
feet three-segmented and the forewings greatly reduced; most of the
species are parasites on birds and bats, but one--_Cimex lectidarius_
(figs. 3, 8)--is the well-known "bed-bug" which abounds in unclean
dwellings and sucks human blood (see BUG). The _Anthocoridae_ are
nearly related to the _Cimicidae_, but the wings are usually well
developed and the forewing possesses cuneus and embolium as well as
corium and clavus. The _Capsidae_ are a large family of rather
soft-skinned bugs mostly elongate in form with the two basal segments
of the feelers stouter than the two terminal. The forewing in this
family has a cuneus (fig. 9 cu), but not an embolium. These insects
are often found in large numbers on plants whose juices they suck.
[Illustration: After M. V. Slingerland, _Cornell Univ. Ent. Bull._ 58.
FIG. 9.--Capsid Leaf-bug (_Poecilocapsus lineatus_) N. America.
Magnified--, cu cuneus.]
[Illustration: From Mariatt, _Bull._ 14 (N. S.), _Div. Ent. U.S. Dept.
Agr._
FIG. 10.--a, Nymph (4th stage) of Cicad, magnified; c, d, inner and
outer faces of front leg, magnified--; b, teeth on thigh, more highly
magnified.]
_Cryptocerata._--In this tribe are included five or six families of
aquatic Heteroptera which spend the greater part of their lives
submerged, diving and swimming through the water. The feelers are very
small and are often hidden in cavities beneath the head. The
_Naucoridae_ and _Belostomatidae_ are flattened insects, with
four-segmented feelers and fore-legs inserted at the front of the
prosternum. Two species of the former family inhabit our islands, but
the _Belostomatidae_ are found only in the warmer regions of the
globe; some of them, attaining a length of 4 to 5 in., are giants
among insects. The _Nepidae_ (fig. 6) or water-scorpions (q.v.)--two
British species--are distinguished by their three-segmented feelers,
their raptorial fore-legs (in which the shin and foot, fused together,
work like a sharp knife-blade on the grooved thigh), and their
elongate tail-processes formed of the abdominal pleura and used for
respiration. The _Notonectidae_, or "water-boatmen" (q.v.) have convex
ovoid bodies admirably adapted for aquatic life. By means of the
oar-like hind-legs they swim actively through the water with the
ventral surface upwards; the fore-legs are inserted at the hinder edge
of the prosternum. The _Corixidae_ are small flattened water-bugs,
with very short unjointed beak, the labrum being enclosed within the
second maxillae, and the foot in the fore and intermediate leg having
but a single segment. The hinder abdominal segments in the male show a
curious asymmetrical arrangement, the sixth segment bearing on its
upper side a small stalked plate (_strigil_) of unknown function,
furnished with rows of teeth. On account of the reduction and
modification of the jaws in the _Corixidae_, C. Borner has lately
suggested that they should form a special sub-order of Hemiptera--the
Sandaliorrhyncha.
HOMOPTERA
This sub-order includes the cicads, lantern-flies, frog-hoppers,
aphids and scale-insects. The face has such a marked backward slope
(see fig. 1) as to bring the beak into close contact with the haunches
of the fore-legs. The feelers have one or more thickened basal
segments, while the remaining segments are slender and thread-like.
The fore-wings are sometimes membranous like the hind-wings, usually
they are firmer in texture, but they never show the distinct areas
that characterize the wings of Heteroptera. When at rest the wings of
Homoptera slope roofwise across the back of the insect. In their
life-history the Homoptera are more specialized than the Heteroptera;
the young insect often differs markedly from its parent and does not
live in the same situations; while in some families there is a passive
stage before the last moult.
[Illustration: After Weed, Riley and Howard, _Insect Life_, vol iii.
FIG. 11.--Cabbage Aphid (_Aphisbrassicae_). a, Male; c, female
(wingless). Magnified. b and d, Head and feelers of male and female,
more highly magnified.]
[Illustration: After Howard, _Year Book U.S. Dept. Agr._, 1894.
FIG. 12.--Apple Scale Insect (_Mytilaspis pomorum_). a, Male; e,
female; c, larva magnified--; b, foot of male; d, feeler of larva,
more highly magnified.]
The _Cicadidae_ are for the most part large insects with ample wings;
they are distinguished from other Homoptera by the front thighs being
thickened and toothed beneath. The broad head carries, in addition to
the prominent compound eyes, three simple eyes (ocelli) on the crown,
while the feeler consists of a stout basal segment, followed by five
slender segments. The female, by means of her serrated ovipositor,
lays her eggs in slits cut in the twigs of plants. The young have
simple feelers and stout fore-legs (fig. 10) adapted for digging; they
live underground and feed on the roots of plants. In the case of a
North American species it is known that this larval life lasts for
seventeen years. The "song" of the male cicads is notorious and the
structures by which it is produced have already been described (see
also CICADA). There are about 900 known species, but the family is
mostly confined to warm countries; only a single cicad is found in
England, and that is restricted to the south.
The _Fulgoridae_ and _Membracidae_ are two allied families most of
whose members are also natives of hot regions. The _Fulgoridae_ have
the head with two ocelli and three-segmented feelers; frequently as in
the tropical "lantern-flies" (q.v.) the head is prolonged into a
conspicuous bladder, or trunk-like process. The _Membracidae_ are
remarkable on account of the backward prolongation of the pronotum
into a process or hood-like structure which may extend far behind the
tail-end of the abdomen. Two other allied families, the _Cercopidae_
and _Jassidae_, are more numerously represented in our islands. The
young of many of these insects are green and soft-skinned, protecting
themselves by the well-known frothy secretion that is called
"cuckoo-spit."
[Illustration: After Howard, _Year Book U.S. Dept. Agr._, 1894.
FIG. 13.--Apple Scale Insect (_Mytilaspis pomorum_). a, Scale from
beneath showing female and eggs; b, from above, magnified--; c and e,
female and male scales on twigs, natural size; d, male scale
magnified.]
[Illustration: From Osborn (after Denny), _Bull._ 5 (N.S.), _Div. Ent.
U.S. Dept. Agr._
FIG. 14.--Louse (_Pediculus vestimenti_). Magnified.]
[Illustration: From Osborn (after Schiodte), _Bull._ 5; (N.S.), _Div.
Ent. U.S. Dept. Agr._
FIG. 15.--Proboscis of Pediculus. Highly magnified.]
In all the above-mentioned families of Homoptera there are three
segments in each foot. The remaining four families have feet with only
two segments. They are of very great zoological interest on account of
the peculiarities of their life-history--parthenogenesis being of
normal occurrence among most of them. The families _Psyllidae_ (or
"jumpers") with eight or ten segments in the feeler and the
_Aleyrodidae_ (or "snowy-flies") distinguished by their white mealy
wings, are of comparatively slight importance. The two families to
which special attention has been paid are the _Aphidae_ or plant-lice
("green fly") and the _Coccidae_ or scale-insects. The aphids (fig.
11) have feelers with seven or fewer distinct segments, and the fifth
abdominal segment usually carries a pair of tubular processes through
which a waxy secretion is discharged. The sweet "honey-dew," often
sought as a food by ants, is secreted from the intestines of aphids.
The peculiar life-cycle in which successive generations are produced
through the summer months by virgin females--the egg developing within
the body of the mother--is described at length in the articles APHIDES
and PHYLLOXERA. The _Coccidae_ have only a single claw to the foot;
the males (fig. 12 _a_) have the fore-wings developed and the
hind-wings greatly reduced, while in the female wings are totally
absent and the body undergoes marked degradation (figs. 12, _e_, 13,
_a_, _b_). In the Coccids the formation of a protective waxy
secretion--present in many genera of Homoptera--reaches its most
extreme development. In some coccids--the "mealy-bugs" (_Dactylopius_,
&c.) for example--the secretion forms a white thread-like or
plate-like covering which the insect carries about. But in most
members of the family, the secretion, united with cast cuticles and
excrement, forms a firm "scale," closely attached by its edges to the
surface of the plant on which the insect lives, and serving as a
shield beneath which the female coccid, with her eggs (fig. 13 _a_)
and brood, finds shelter. The male coccid passes through a passive
stage (fig. 4) before attaining the perfect condition. Many
scale-insects are among the most serious of pests, but various species
have been utilized by man for the production of wax (lac) and red dye
(cochineal). See ECONOMIC ENTOMOLOGY, SCALE-INSECT.
ANOPLURA
The Anoplura or lice (see LOUSE) are wingless parasitic insects (fig.
14) forming an order distinct from the Hemiptera, their sucking and
piercing mouth-organs being apparently formed on quite a different
plan from those of the Heteroptera and Homoptera. In front of the head
is a short tube armed with strong recurved hooks which can be fixed
into the skin of the host, and from the tube an elongate more slender
sucking-trunk can be protruded (fig. 15). Each foot is provided with a
single strong claw which, opposed to a process on the shin, serves to
grasp a hair of the host, all the lice being parasites on different
mammals. Although G. Enderlein has recently shown that the jaws of the
Hemiptera can be recognized in a reduced condition in connexion with
the louse's proboscis, the modification is so excessive that the group
certainly deserves ordinal separation.
BIBLIOGRAPHY.--A recent standard work on the morphology of the
Hemiptera by R. Heymons (_Nova Acta Acad. Leop. Carol._ lxxiv. 3,
1899) contains numerous references to older literature. An excellent
survey of the order is given by D. Sharp (_Cambridge Nat. Hist._ vol.
vi., 1898). For internal structure of Heteroptera see R. Dufour, _Mem.
savans etrangers_ (Paris, iv., 1833); of Homoptera, E. Witlaczil
(_Arb. Zool. Inst. Wien_, iv., 1882, _Zeits. f. wiss. Zool._ xliii.,
1885). The development of Aphids has been dealt with by T. H. Huxley
(_Trans. Linn. Soc._ xxii., 1858) and E. Witlaczil (_Zeits. f. wiss.
Zool._ xl., 1884). Fossil Hemiptera are described by S. H. Scudder in
K. Zittel's _Paleontologie_ (French translation, vol. ii. Paris, 1887,
and English edition, vol. i., London, 1900), and by A. Handlirsch
(_Verh. zool. bot. Gesell. Wien_, lii., 1902). Among general
systematic works on Heteroptera may be mentioned J. C. Schiodte (_Ann.
Mag. Nat. Hist._ (4) vi., 1870); C. Stal's _Enumeratio Hemipterorum_
(_K. Svensk. Vet. Akad. Handl._ ix.-xiv., 1870-1876); L. Lethierry and
G. Severin's _Catalogue generale des hemipteres_ (Brussels 1893, &c.);
G. C. Champion's volumes in the _Biologia Centrali-Americana_; W. L.
Distant's Oriental Cicadidae (London, 1889-1892), and many other
papers; M. E. Fernald's _Catalogue of the Coccidae_ (Amherst, U.S.A.,
1903). European Hemiptera have been dealt with in numerous papers by
A. Puton. For British species we have E. Saunders's
_Hemiptera-Heteroptera of the British Isles_ (London, 1892); J.
Edwards's Hemiptera-Homoptera of the British Isles (London, 1896); J.
B. Buckton's _British Aphidae_ (London, Ray Society, 1875-1882); and
R. Newstead's _British Coccidae_ (London, Ray Society, 1901-1903).
Aquatic Hemiptera are described by L. C. Miall (_Nat. History Aquatic
Insects_; London, 1895), and by G. W. Kirkaldy in numerous recent
papers (_Entomologist_, &c.). For marine Hemiptera (_Halobates_) see
F. B. White (_Challenger Reports_, vii., 1883); J. J. Walker (_Ent.
Mo. Mag._, 1893); N. Nassonov (Warsaw, 1893), and G. H. Carpenter
(_Knowledge_, 1901, and _Report, Pearl Oyster Fisheries, Royal
Society_, 1906). Sound-producing organs of Heteroptera are described
by A. Handlirsch (_Ann. Hofmus. Wien_, xv. 1900), and G. W. Kirkaldy
(_Journ. Quekett Club_ (2) viii. 1901); of Cicads by G. Carlet (_Ann.
Sci. Nat. Zool._ (6) v. 1877). For the Anoplura see E. Piaget's
_Pediculines_ (Leiden, 1880-1905), and G. Enderlein (_Zool. Anz._
xxviii., 1904). (G. H. C.)
HEMLOCK (in O. Eng. _hemlic_ or _hymlice_; no cognate is found in any
other language, and the origin is unknown), the _Conium maculatum_ of
botanists, a biennial umbelliferous plant, found wild in many parts of
Great Britain and Ireland, where it occurs in waste places on
hedge-banks, and by the borders of fields, and also widely spread over
Europe and temperate Asia, and naturalized in the cultivated districts
of North and South America. It is an erect branching plant, growing from
3 to 6 ft. high, and emitting a disagreeable smell, like that of mice.
The stems are hollow, smooth, somewhat glaucous green, spotted with dull
dark purple, as alluded to in the specific name, _maculatum_. The
root-leaves have long furrowed footstalks, sheathing the stem at the
base, and are large, triangular in outline, and repeatedly divided or
compound, the ultimate and very numerous segments being small, ovate,
and deeply incised at the edge. These leaves generally perish after the
growth of the flowering stem, which takes place in the second year,
while the leaves produced on the stem became gradually smaller upwards.
The branches are all terminated by compound many-rayed umbels of small
white flowers, the general involucres consisting of several, the partial
ones of about three short lanceolate bracts, the latter being usually
turned towards the outside of the umbel. The flowers are succeeded by
broadly ovate fruits, the mericarps (half-fruits) having five ribs
which, when mature, are waved or crenated; and when cut across the
albumen is seen to be deeply furrowed on the inner face, so as to
exhibit in section a reniform outline. The fruits when triturated with a
solution of caustic potash evolve a most unpleasant odour.
Hemlock is a virulent poison, but it varies much in potency according to
the conditions under which it has grown, and the season or stage of
growth at which it is gathered. In the first year the leaves have little
power, nor in the second are their properties developed until the
flowering period, at which time, or later on when the fruits are fully
grown, the plant should be gathered. The wild plant growing in exposed
situations is to be preferred to garden-grown samples, and is more
potent in dry warm summers than in those which are dull and moist.
The poisonous property of hemlock resides chiefly in the alkaloid
_conine_ or _conia_ which is found in both the fruits and the leaves,
though in exceedingly small proportions in the latter. Conine resembles
nicotine in its deleterious action, but is much less powerful. No
chemical antidote for it is known. The plant also yields a second less
poisonous crystallizable base called _conhydrine_, which may be
converted into conine by the abstraction of the elements of water. When
collected for medicinal purposes, for which both leaves and fruits are
used, the former should be gathered at the time the plant is in full
blossom, while the latter are said to possess the greatest degree of
energy just before they ripen. The fruits are the chief source whence
conine is prepared. The principal forms in which hemlock is employed are
the extract and juice of hemlock, hemlock poultice, and the tincture of
hemlock fruits. Large doses produce vertigo, nausea and paralysis; but
in smaller quantities, administered by skilful hands, it has a sedative
action on the nerves. It has also some reputation as an alterative and
resolvent, and as an anodyne.
The acrid narcotic properties of the plant render it of some importance
that one should be able to identify it, the more so as some of the
compound-leaved umbellifers, which have a general similarity of
appearance to it, form wholesome food for man and animals. Not only is
this knowledge desirable to prevent the poisonous plant being
detrimentally used in place of the wholesome one; it is equally
important in the opposite case, namely, to prevent the inert being
substituted for the remedial agent. The plant with which hemlock is most
likely to be confounded is _Anthriscus sylvestris_, or cow-parsley, the
leaves of which are freely eaten by cattle and rabbits; this plant, like
the hemlock, has spotted stems but they are hairy, not hairless; it has
much-divided leaves of the same general form, but they are downy and
aromatic, not smooth and nauseous when bruised; and the fruit of
_Anthriscus_ is linear-oblong and not ovate.
HEMP (in O. Eng. _henep_, cf. Dutch _hennep_, Ger. _Hanf_, cognate with
Gr. [Greek: kannabis], Lat. _cannabis_), an annual herb (_Cannabis
sativa_) having angular rough stems and alternate deeply lobed leaves.
The bast fibres of _Cannabis_ are the hemp of commerce, but,
unfortunately, the products from many totally different plants are often
included under the general name of hemp. In some cases the fibre is
obtained from the stem, while in others it comes from the leaf. Sunn
hemp, Manila hemp, Sisal hemp, and Phormium (New Zealand flax, which is
neither flax nor hemp) are treated separately. All these, however, are
often classed under the above general name, and so are the
following:--Deccan or Ambari hemp, _Hibiscus cannabinus_, an Indian and
East Indian malvaceous plant, the fibre from which is often known as
brown hemp or Bombay hemp; Pite hemp, which is obtained from the
American aloe, _Agave americana_; and Moorva or bowstring-hemp,
_Sansevieria zeylanica_, which is obtained from an aloe-like plant, and
is a native of India and Ceylon. Then there are Canada hemp, _Apocynum
cannabinum_, Kentucky hemp, _Urtica cannabina_, and others.
The hemp plant, like the hop, which is of the same natural order,
Cannabinaceae, is dioecious, i.e. the male and female flowers are borne
on separate plants. The female plant grows to a greater height than the
male, and its foliage is darker and more luxuriant, but the plant takes
from five to six weeks longer to ripen. When the male plants are ripe
they are pulled, put up into bundles, and steeped in a similar manner to
flax, but the female plants are allowed to remain until the seed is
perfectly ripe. They are then pulled, and after the seed has been
removed are retted in the ordinary way. The seed is also a valuable
product; the finest is kept for sowing, a large quantity is sold for the
food of cage birds, while the remainder is sent to the oil mills to be
crushed. The extracted oil is used in the manufacture of soap, while the
solid remains, known as oil-cake, are valuable as a food for cattle. The
leaves of hemp have five to seven leaflets, the form of which is
lanceolate-acuminate, with a serrate margin. The loose panicles of male
flowers, and the short spikes of female flowers, arise from the axils of
the upper leaves. The height of the plant varies greatly with season,
soil and manuring; in some districts it varies from 3 to 8 ft., but in
the Piedmont province it is not unusual to see them from 8 to 16 ft. in
height, whilst a variety (_Cannabis sativa_, variety gigantea) has
produced specimens over 17 ft. in height.
All cultivated hemp belongs to the same species, _Cannabis sativa_; the
special varieties such as _Cannabis indica_, _Cannabis chinensis_, &c.,
owe their differences to climate and soil, and they lose many of their
peculiarities when cultivated in temperate regions. Rumphius (in the
17th century) had noticed these differences between Indian and European
hemp.
Wild hemp still grows on the banks of the lower Ural, and the Volga,
near the Caspian Sea. It extends to Persia, the Altai range and northern
and western China. The authors of the _Pharmacographia_ say:--"It is
found in Kashmir and in the Himalaya, growing 10 to 12 ft. high, and
thriving vigorously at an elevation of 6000 to 10,000 ft." Wild hemp is,
however, of very little use as a fibre producer, although a drug is
obtained from it.
It would appear that the native country of the hemp plant is in some
part of temperate Asia, probably near the Caspian Sea. It spread
westward throughout Europe, and southward through the Indian peninsula.
The names given to the plant and to its products in different countries
are of interest in connexion with the utilization of the fibre and
resin. In Sans. it is called _goni_, _sana_, _shanapu_, _banga_ and
_ganjika_; in Bengali, _ganga_; Pers. _bang_ and _canna_; Arab. _kinnub_
or _cannub_; Gr. _kannabis_; Lat. _cannabis_; Ital. _canappa_; Fr.
_chanvre_; Span. _canamo_; Portuguese, _canamo_; Russ. _konopel_;
Lettish and Lithuanian, _kannapes_; Slav. _konopi_; Erse, _canaib_ and
_canab_; A. Sax. _hoenep_; Dutch, _hennep_; Ger. _Hanf_; Eng. _hemp_;
Danish and Norwegian, _hamp_; Icelandic, _hampr_; and in Swed. _hampa_.
The English word _canvas_ sufficiently reveals its derivation from
_cannabis_.