Chapter IV: CYSTOPHORIDA (Cystonectae, Haeckel). With a very large (3)

These figures do not include cases which develop hydrophobia during treatment or within fifteen days after treatment is completed, for it is held that persons who die within that period have their nervous centres invaded by virus before the cure has time to act. The true mortality should therefore be considerably higher. For instance, in 1898 three deaths came within this category, which just doubles the mortality; and in 1899 the additional deaths were six, bringing the mortality up to two-and-a-half times that indicated in the table. When, however, the additional deaths are included the results remain sufficiently striking, if two assumptions are granted--(1) that all the persons treated have been bitten by rabid animals; (2) that a large proportion of persons so bitten usually have hydrophobia. Unfortunately, both these assumptions lack proof, and therefore the evidence of the efficacy of the treatment cannot be said to satisfy a strictly scientific standard. With regard to the first point, the patients are divided into three categories--(1) those bitten by an animal the rabidity of which is proved by the development of rabies in other animals bitten by it or inoculated from its spinal cord; (2) those bitten by an animal pronounced rabid on a veterinary examination; (3) those bitten by an animal suspected of being rabid. The number of patients in each category in 1898 was (1) 141, (2) 855, (3) 469; and in 1899 it was (1) 152, (2) 1099, (3) 363. As might be expected, the vast majority came under the second and third heads, in which the evidence of rabidity is doubtful or altogether lacking. With regard to the second point, the proportion of persons bitten by rabid animals who ordinarily develop hydrophobia has only been "estimated" from very inadequate data. Otto Bollinger from a series of collected statistics states that before the introduction of the Pasteur treatment, of patients bitten by dogs undoubtedly rabid 47% died, the rate being 33% in those whose wounds had been cauterized and 83% when there had been no local treatment. If the number of rabid dogs be compared with the deaths from hydrophobia in any year or series of years, it can hardly be very high. For instance, in 1895, 668 dogs, besides other animals, were killed and certified to be rabid in England, and the deaths from hydrophobia were twenty. Of course this proves nothing, as the number of persons bitten is not known, but the difference between the amount of rabies and of hydrophobia is suggestively great in view of the marked propensity of rabid dogs to bite, nor is it accounted for by the fact that some of the persons bitten were treated at the Institut Pasteur. A comparison of the annual mortality from hydrophobia in France before and after the introduction of the treatment would afford decisive evidence as to its efficacy; but unfortunately no such comparison can be made for lack of vital statistics in that country. The experience of the Paris hospitals, however, points to a decided diminution of mortality. On the whole it must be said, in the absence of further data, that the Pasteur treatment certainly diminishes the danger of hydrophobia from the bites of rabid animals.

More recently treatment with an anti-rabic serum has been suggested (see PARASITIC DISEASES). Victor Babes and Lepp and later Guido Tizzoni and Eugenio Centanni have worked out a method of serum treatment curative and protective. In this method not the rabic poison itself, as in the Pasteur treatment, but the protective substance formed is injected into the tissues. The serum of a vaccinated animal is capable of neutralizing the power of the virus of rabies not only when mixed with the virus before injection but even when injected simultaneously or within twenty-four hours after the introduction of the virus. These authors showed that the serum of a rabbit protects a rabbit better than does the serum of a dog, and vice versa. At the end of twenty days' injections they found they could obtain such a large quantity of anti-rabic substance in the serum of an animal, that even 1 part of serum to 25,000 of the body weight would protect an animal. This process differs from that of Pasteur in so far as that in place of promoting the formation of the antidote within the body of the patient, by a process of vaccination with progressively stronger and stronger virus, this part of the process is carried on in an animal, Babes using the dog and Centanni the sheep, the blood serum of which is injected. This method of vaccination is useful as a protective to those in charge of kennels.

Muzzling order in England.

The attempt to stamp out rabies in Great Britain was an experiment undertaken by the government in the public interest. The principal means adopted were the muzzling of dogs in infected areas, and prolonged quarantine for imported animals. The efficacy of dog-muzzling in checking the spread of rabies and diminishing its prevalence has been repeatedly proved in various countries. Liable as other animals may be to the disease, in England at least the dog is pre-eminently the vehicle of contagion and the great source of danger to human beings. There is a difference of opinion on the way in which muzzling acts, though there can be none as to the effect it produces in reducing rabies. Probably it acts rather by securing the destruction of ownerless and stray--which generally includes rabid--dogs than by preventing biting; for though it may prevent snapping, even the wire-cage muzzle does not prevent furious dogs from biting, and it is healthy, not rabid, dogs that wear the muzzle. It has therefore been suggested that a collar would have the same effect, if all collarless dogs were seized; but the evidence goes to show that it has not, perhaps because rabid dogs are more likely to stray from home with their collars, which are constantly worn, than with muzzles which are not, and so escape seizure. Moreover, it is much easier for the police to see whether a dog is wearing a muzzle or not than it is to make sure about the collar. However this may be, the muzzle has proved more efficacious, but it was not applied systematically in England until a late date. Sometimes the regulations were in the hands of the government, and sometimes they were left to local authorities; in either case they were allowed to lapse as soon as rabies had died down. In April 1897 the Board of Agriculture entered on a systematic attempt to exterminate rabies by the means indicated. The plan was to enforce muzzling over large areas in which the disease existed, and to maintain it for six months after the occurrence of the last case. In spite of much opposition and criticism, this was resolutely carried out under Mr Walter Long, the responsible minister, and met with great success. By the spring of 1899--that is, in two years--the disease had disappeared in Great Britain, except for one area in Wales; and, with this exception, muzzling was everywhere relaxed in October 1899. It was taken off in Wales also in the following May, no case having occurred since November 1899. Rabies was then pronounced extinct. During the summer of 1900, however, it reappeared in Wales, and several counties were again placed under the order. The year 1901 was the third in succession in which no death from hydrophobia was registered in the United Kingdom. In the ten years preceding 1899, 104 deaths were registered, the death-rate reaching 30 in 1889 and averaging 29 annually. In 1902 two deaths from hydrophobia were registered. From that date to June 1909 (the latest available for the purpose of this article) no death from hydrophobia was notified in the United Kingdom.

See _Annales de l'Institut Pasteur_, from 1886; _Journal of the Board
of Agriculture_, 1899; Makins, "Hydrophobia," in Treves's _System of
Surgery_; Woodhead, "Rabies," in Allbutt's _System of Medicine_.

HYDROSPHERE (Gr. [Greek: hydôr], water, and [Greek: sphaira], sphere), in physical geography, a name given to the whole mass of the water of the oceans, which fills the depressions in the earth's crust, and covers nearly three-quarters of its surface. The name is used in distinction from the atmosphere, the earth's envelope of air, the lithosphere (Gr. [Greek: lithos], rock) or solid crust of the earth, and the centrosphere or interior mass within the crust. To these "spheres" some writers add, by figurative usage, the terms "biosphere," or life-sphere, to cover all living things, both animals and plants, and "psychosphere," or mind-sphere, covering all the products of human intelligence.

HYDROSTATICS (Gr. [Greek: hydôr], water, and the root [Greek: sta]-, to cause to stand), the branch of hydromechanics which discusses the equilibrium of fluids (see HYDROMECHANICS).

HYDROXYLAMINE, NH2OH, or hydroxy-ammonia, a compound prepared in 1865 by W. C. Lossen by the reduction of ethyl nitrate with tin and hydrochloric acid. In 1870 E. Ludwig and T. H. Hein (_Chem. Centralblatt_, 1870, 1, p. 340) obtained it by passing nitric oxide through a series of bottles containing tin and hydrochloric acid, to which a small quantity of platinum tetrachloride has been added; the acid liquid is poured off when the operation is completed, and sulphuretted hydrogen is passed in; the tin sulphide is filtered off and the filtrate evaporated. The residue is extracted by absolute alcohol, which dissolves the hydroxylamine hydrochloride and a little ammonium chloride; this last substance is removed as ammonium platino-chloride, and the residual hydroxylamine hydrochloride is recrystallized. E. Divers obtains it by mixing cold saturated solutions containing one molecular proportion of sodium nitrate, and two molecular proportions of acid sodium sulphite, and then adding a saturated solution of potassium chloride to the mixture. After standing for twenty-four hours, hydroxylamine potassium disulphonate crystallizes out. This is boiled for some hours with water and the solution cooled, when potassium sulphate separates first, and then hydroxylamine sulphate. E. Tafel (_Zeit. anorg. Chem._, 1902, 31, p. 289) patented an electrolytic process, wherein 50% sulphuric acid is treated in a divided cell provided with a cathode of amalgamated lead, 50% nitric acid being gradually run into the cathode compartment. Pure anhydrous hydroxylamine has been obtained by C. A. Lobry de Bruyn from the hydrochloride, by dissolving it in absolute methyl alcohol and then adding sodium methylate. The precipitated sodium chloride is filtered, and the solution of hydroxylamine distilled in order to remove methyl alcohol, and finally fractionated under reduced pressure. The free base is a colourless, odourless, crystalline solid, melting at about 30° C., and boiling at 58° C. (under a pressure of 22 mm.). It deliquesces and oxidizes on exposure, inflames in dry chlorine and is reduced to ammonia by zinc dust. Its aqueous solution is strongly alkaline, and with acids it forms well-defined stable salts. E. Ebler and E. Schott (_J. pr. Chem._, 1908, 78, p. 289) regard it as acting with the formula NH2·OH towards bases, and as NH3:O towards acids, the salts in the latter case being of the oxonium type. It is a strong reducing agent, giving a precipitate of cuprous oxide from alkaline copper solutions at ordinary temperature, converting mercuric chloride to mercurous chloride, and precipitating metallic silver from solutions of silver salts. With aldehydes and ketones it forms oximes (q.v.). W. R. Dunstan (_Jour. Chem. Soc._, 1899, 75, p. 792) found that the addition of methyl iodide to a methyl alcohol solution of hydroxylamine resulted in the formation of trimethyloxamine, N(CH3)3O.

Many substituted hydroxylamines are known, substitution taking place
either in the [alpha] or [beta] position

[beta] [alpha]
(NH2 · OH^).

[beta]-phenylhydroxyl-amine, C6H5NH·OH·, is obtained in the reduction
of nitrobenzene in neutral solution (e.g. by the action of the
aluminium-mercury couple and water), but better, according to C.
Goldschmidt (_Ber._, 1896, 29, p. 2307) by dissolving nitrobenzene in
ten times its weight of ether containing a few cubic centimetres of
water, and heating with excess of zinc dust and anhydrous calcium
chloride for three hours on a water bath. It also appears as an
intermediate product in the electrolytic reduction of nitrobenzene in
sulphuric acid solution. By gentle oxidation it yields nitrosobenzene.
Derivatives of the type R2N·OH result in the action of the Grignard
reagent on amyl nitrite. Dihydroxy-ammonia or nitroxyl, NH(OH)2, a
very unstable and highly reactive substance, has been especially
studied by A. Angeli (see A. W. Stewart, _Recent Advances in Physical
and Inorganic Chemistry_, 1909).

HYDROZOA, one of the most widely spread and prolific groups of aquatic animals. They are for the most part marine in habitat, but a familiar fresh-water form is the common _Hydra_ of ponds and ditches, which gives origin to the name of the class. The Hydrozoa comprise the hydroids, so abundant on all shores, most of which resemble vegetable organisms to the unassisted eye; the hydrocorallines, which, as their name implies, have a massive stony skeleton and resemble corals; the jelly-fishes so called; and the Siphonophora, of which the species best known by repute is the so-called "Portuguese man-of-war" (_Physalia_), dreaded by sailors on account of its terrible stinging powers.

In external form and appearance the Hydrozoa exhibit such striking differences that there would seem at first sight to be little in common between the more divergent members of the group. Nevertheless there is no other class in the animal kingdom with better marked characteristics, or with more uniform morphological peculiarities underlying the utmost diversity of superficial characters.

All Hydrozoa, in the first place, exhibit the three structural features distinctive of the Coelentera (q.v.). (1) The body is built up of two layers only, an external protective and sensory layer, the ectoderm, and an internal digestive layer, the endoderm. (2) The body contains but a single internal cavity, the coelenteron or gastrovascular space, which may be greatly ramified, but is not shut off into cavities distinct from the central digestive space. (3) The generative cells are produced in either the ectoderm or endoderm, and not in a third layer arising in the embryo, distinct from the two primary layers; in other words, there is no mesoderm or coelom.

To these three characters the Hydrozoa add a fourth which is distinctive of the subdivision of the Coelenterata termed the Cnidaria; that is to say, they always possess peculiar stinging organs known as nettle-cells, or _nematocysts_ (_Cnidae_), each produced in a cell forming an integral part of the animal's tissues. The Hydrozoa are thus shown to belong to the group of Coelenterata Cnidaria, and it remains to consider more fully their distinctive features, and in particular those which mark them off from the other main division of the Cnidaria, the Anthozoa (q.v.), comprising the corals and sea-anemones.

The great diversity, to which reference has already been made, in the form and structure of the Hydrozoa is due to two principal causes. In the first place, we find in this group two distinct types of person or individual, the polyp and the medusa (qq.v.), each capable of a wide range of variations; and when both polyp and medusa occur in the life-cycle of the same species, as is frequently the case, the result is an alternation of generations of a type peculiarly characteristic of the class. In the second place, the power of non-sexual reproduction by budding is practically of universal occurrence among the Hydrozoa, and by the buds failing to separate from the parent stock, colonies are produced, more or less complicated in structure and often of great size. We find that polyps may either bud other polyps or may produce medusae, and that medusae may bud medusae, though never, apparently, polyps. Hence we have a primary subdivision of the colonies of Hydrozoa into those produced by budding of polyps and those produced by budding of medusae. The former may contain polyp-persons and medusa-persons, either one kind alone or both kinds combined; the latter will contain only medusa-persons variously modified.

The morphology of the Hydrozoa reduces itself, therefore, to a consideration of the morphology of the polyp, of the medusa and of the colony. Putting aside the last-named, for a detailed account of which see HYDROMEDUSAE, we can best deal with the peculiarities of the polyp and medusa from a developmental point of view.

In the development of the Hydrozoa, and indeed of the Cnidaria
generally, the egg usually gives rise to an oval larva which swims
about by means of a coating of cilia on the surface of the body. This
very characteristic larva is termed a _planula_, but though very
uniform externally, the planulae of different species, or of the same
species at different periods, do not always represent the same stage
of embryonic development internally. On examining more minutely the
course of the development, it is found that the ovum goes through the
usual process of cleavage, always total and regular in this group, and
so gives rise to a hollow sphere or ovoid with the wall composed of a
single layer of cells, and containing a spacious cavity, the
blastocoele or segmentation-cavity. This is the _blastula_ stage
occurring universally in all Metazoa, probably representing an
ancestral Protozoan colony in phylogeny. Next the blastula gives rise
to an internal mass of cells (fig. 1, hy) which come from the wall
either by immigration (fig. 1, A) or by splitting off (delamination).
The formation of an inner cell-mass converts the single-layered
blastula (monoblastula) into a double-layered embryo (diblastula)
which may be termed a parenchymula, since at first the inner cell-mass
forms an irregular parenchyma which may entirely fill up and
obliterate the segmentation cavity (fig. 1, B). At a later stage,
however, the cells of the inner mass arrange themselves in a definite
layer surrounding an internal cavity (fig. 1, C, al), which soon
acquires an opening to the exterior at one pole, and so forms the
characteristic embryonic stage of all Enterozoa known as the
_gastrula_ (fig. 2). In this stage the body is composed of two layers,
ectoderm (d) externally, and endoderm (c) internally, surrounding a
central cavity, the _archenteron_ (b), which communicates with the
exterior by a pore (a), the _blastopore_.

Thus a planula larva may be a blastula, or but slightly advanced
beyond this stage, or it may be (and most usually is) a parenchymula;
or in some cases (Scyphomedusae) it may be a gastrula. It should be
added that the process of development, the gastrulation as it is
termed, may be shortened by the immigration of cells taking place at
one pole only, and in a connected layer with orderly arrangement, so
that the gastrula stage is reached at once from the blastula without
any intervening parenchymula stage. This is a process of gastrulation
by invagination which is found in all animals above the Coelenterata,
but which is very rare in the Cnidaria, and is known only in the
Scyphomedusae amongst the Hydrozoa.

FIG. 1.--Formation of the Diblastula of _Eucope_ (one of the
Calyptoblastic _Hydromedusae_) by immigration. A, B, C, three
successive stages. _ep_, Ectoderm; _hy_, endoderm; _al_, enteric
cavity.]

After the gastrula stage, which is found as a developmental stage in
all Enterozoa, the embryo of the Hydrozoa proceeds to develop
characters which are peculiar to the Coelenterata only. Round the
blastopore hollow outgrowths, variable in number, arise by the
evagination of the entire body-wall, both ectoderm and endoderm. Each
outgrowth contains a prolongation of the archenteric cavity (compare
figs. 2 and 3, A). In this way is formed a ring of tentacles, the most
characteristic organs of the Cnidaria. They surround a region which is
termed the peristome, and which contains in the centre the blastopore,
which becomes the adult mouth. The archenteron becomes the
gastrovascular system or coelenteron. Between the ectoderm and
endoderm a gelatinous supporting layer, termed the mesogloea, makes
its appearance. The gastrula has now become an _actinula_, which may
be termed the distinctive larva of the Cnidaria, and doubtless
represents in a transitory manner the common ancestor of the group. In
no case known, however, does the actinula become the adult, sexually
mature individual, but always undergoes further modifications, whereby
it develops into either a polyp or a medusa.

FIG. 2.--Diagram of a Diblastula.

a, Blastopore.
b, Archenteric cavity.
c, Endoderm.
d, Ectoderm.]

To become a polyp, the actinula (fig. 3, A) becomes attached to some
firm object by the pole farthest from the mouth, and its growth
preponderates in the direction of the principal axis, that is to say,
the axis passing through the mouth (fig. 3, _a-b_). As a result the
body becomes columnar in form (fig. 3, B), and without further change
passes into the characteristic polyp-form (see POLYP).

It is convenient to distinguish two types of polyp by the names hydro
polyp and anthopolyp, characteristic of the Hydrozoa and Anthozoa
respectively. In the hydropolyp the body is typically elongated, the
height of the column being far greater than the diameter. The
peristome is relatively small and the mouth is generally raised on a
projecting spout or _hypostome_. The ectoderm loses entirely the
ciliation which it had in the planula and actinula stages and commonly
secretes on its external surface a protective or supporting
investment, the perisarc. Contrasting with this, the anthopolyp is
generally of squat form, the diameter often exceeding the height; the
peristome is wide, a hypostome is lacking, and the ectoderm, or so
much of it as is exposed, i.e. not covered by secretion of skeletal or
other investment, retains its ciliation throughout life. The internal
structural differences are even more characteristic. In the hydropolyp
the blastopore of the embryo forms the adult mouth situated at the
extremity of the hypostome, and the ectoderm and endoderm meet at this
point. In the anthopolyp the blastopore is carried inwards by an
in-pushing of the body-wall of the region of the peristome, so that
the adult mouth is an opening leading into a short ectodermal
oesophagus or stomodaeum, at the bottom of which is the blastopore.
Further, in the hydropolyp the digestive cavity either remains simple
and undivided and circular in transverse section, or may show ridges
projecting internally, which in this case are formed of endoderm
alone, without any participation of the mesogloea. In the anthopolyp,
on the other hand, the digestive cavity is always subdivided by
so-called mesenteries, in-growths of the endoderm containing vertical
lamellae of mesogloea (see ANTHOZOA). In short, the hydropolyp is
characterized by a more simple type of organization than the
anthopolyp, and is in most respects less modified from the actinula
type of structure.

Returning now to the actinula, this form may, as already stated,
develop into a medusa, a type of individual found only in the
Hydrozoa, as here understood. To become a medusa, the actinula grows
scarcely at all in the direction of the principal axis, but greatly
along a plane at right angles to it. Thus the body becomes
umbrella-shaped, the concave side representing the peristome, and the
convex side the column, of the polyp. Hence the tentacles are found at
the edge of the umbrella, and the hypostome forms usually a projecting
tube, with the mouth at the extremity, forming the _manubrium_ or
handle of the umbrella. The medusa has a pronounced radial symmetry,
and the positions of the primary tentacles, usually four in number,
mark out the so-called _radii_, alternating with which are four
_interradii_. The ectoderm retains its ciliation only in the sensory
organs. The mesogloea becomes enormously increased in quantity (hence
the popular name "jelly-fish"), and in correlation with this the
endoderm-layer lining the coelenteron becomes pressed together in the
interradial areas and undergoes concrescence, forming a more or less
complicated gastrovascular system (see MEDUSA). It is sufficient to
state here that the medusa is usually a free-swimming animal, floating
mouth downwards on the open seas, but in some cases it may be attached
by its aboral pole, like a polyp, to some firm basis, either
temporarily or permanently.

Thus the development of the two types of individual seen in the
Hydrozoa may be summarized as follows:--

/ Egg
| |
Free | Blastula
| |
"Planula" < Parenchymula
| |
Stage | Gastrula
| |
\ Actinula
/ \
/ \
Polyp Medusa

This development, though probably representing the primitive sequence
of events, is never actually found in its full extent, but is always
abbreviated by omission or elimination of one or more of the stages.
We have already seen that the parenchymula stage is passed over when
the gastrulation is of the invaginate type. On the other hand, the
parenchymula may develop directly into the actinula or even into the
polyp, with suppression of the intervening steps. Great apparent
differences may also be brought about by variations in the period at
which the embryo is set free as a larva, and since two free-swimming
stages, planula and actinula, are unnecessary, one or other of them is
always suppressed. A good example of this is seen in two common genera
of British hydroids, _Cordylophora_ and _Tabularia_. In _Cordylophora_
the embryo is set free at the parenchymula stage as a planula which
fixes itself and develops into a polyp, both gastrula and actinula
stages being suppressed. In _Tubularia_, on the other hand, the
parenchymula develops into an actinula within the maternal tissues,
and is then set free, creeps about for a time, and after fixing
itself, changes into a polyp; hence in this case the planula-stage, as
a free larva, is entirely suppressed.

The Hydrozoa may be defined, therefore, as Cnidaria in which two types
of individual, the polyp and the medusa, may be present, each type
developed along divergent lines from the primitive actinula form. The
polyp (hydropolyp) is of simple structure and never has an ectodernal
oesophagus or mesenteries.[1] The general ectoderm loses its cilia,
which persist only in the sensory cells, and it frequently secretes
external protective or supporting structures. An internal mesogloeal
skeleton is not found.

The class is divisible into two main divisions or sub-classes,
Hydromedusae and Scyphomedusae, of which definitions and detailed
systematic accounts will be found under these headings.

GENERAL WORKS ON HYDROZOA.--C. Chun, "Coelenterata (Hohlthiere),"
_Bronn's Klassen und Ordnungen des Thier-Reichs_ ii. 2 (1889 et seq.);
Y. Delage, and E. Hérouard, _Traité de zoologie concrète_, ii. part 2,
_Les Coelentérés_ (1901); G. H. Fowler, "The Hydromedusae and
Scyphomedusae" in E. R. Lankester's _Treatise on Zoology_, ii.
chapters iv. and v. (1900); S. J. Hickson, "Coelenterata and
Ctenophora," _Cambridge Natural History_, i. chapters x.-xv. (1906).
(E. A. M.)

FOOTNOTE:

[1] See further under SCYPHOMEDUSAE.

HYENA, a name applicable to all the representatives of the mammalian family _Hyaenidae_, a group of Carnivora (q.v.) allied to the civets. From all other large Carnivora except the African hunting-dog, hyenas are distinguished by having only four toes on each foot, and are further characterized by the length of the fore-legs as compared with the hind pair, the non-retractile claws, and the enormous strength of the jaws and teeth, which enables them to break the hardest bones and to retain what they have seized with unrelaxing grip.

The striped hyena (_Hyaena striata_) is the most widely distributed species, being found throughout India, Persia, Asia Minor, and North and East Africa, the East African form constituting a distinct race, _H. striata schillingsi_; while there are also several distinct Asiatic races. The species resembles a wolf in size, and is greyish-brown In colour, marked with indistinct longitudinal stripes of a darker hue, while the legs are transversely striped. The hairs on the body are long, especially on the ridge of the neck and back, where they form a distinct mane, which is continued along the tail. Nocturnal in habits, it prefers by day the gloom of caves and ruins, or of the burrows which it occasionally forms, and issues forth at sunset, when it commences its unearthly howling. When the animal is excited, the howl changes into what has been compared to demoniac laughter, whence the name of "laughing-hyena." These creatures feed chiefly on carrion, and thus perform useful service by devouring remains which might otherwise pollute the air. Even human dead are not safe from their attacks, their powerful claws enabling them to gain access to newly interred bodies in cemeteries. Occasionally (writes Dr W. T. Blanford) sheep or goats, and more often dogs, are carried off, and the latter, at all events, are often taken alive to the animal's den. This species appears to be solitary in habits, and it is rare to meet with more than two together. The cowardice of this hyena is proverbial; despite its powerful teeth, it rarely attempts to defend itself. A very different animal is the spotted hyena, _Hyaena (Crocuta) crocuta_, which has the sectorial teeth of a more cat-like type, and is marked by dark-brown spots on a yellowish ground, while the mane is much less distinct. At the Cape it was formerly common, and occasionally committed great havoc among the cattle, while it did not hesitate to enter the Kaffir dwellings at night and carry off children sleeping by their mothers. By persistent trapping and shooting, its numbers have now been considerably reduced, with the result, however, of making it exceedingly wary, so that it is not readily caught in any trap with which it has had an opportunity of becoming acquainted. Its range extends from Abyssinia to the Cape. The Abyssinian form has been regarded as a distinct species, under the name of _H. liontiewi_, but this, like various more southern forms, is but regarded as a local race. The brown hyena (_H. brunnea_) is South African, ranging to Angola on the west and Kilimanjaro on the east. In size it resembles the striped hyena, but differs in appearance, owing to the fringe of long hair covering the neck and fore part of the back. The general hue is ashy-brown, with the hair lighter on the neck (forming a collar), chest and belly; while the legs are banded with dark brown. This species is not often seen, as it remains concealed during the day. Those frequenting the coast feed on dead fish, crabs and an occasional stranded whale, though they are also a danger to the sheep and cattle kraal. Strand-wolf is the local name at the Cape.

Although hyenas are now confined to the warmer regions of the Old World, fossil remains show that they had a more northerly range during Tertiary times; the European cave-hyena being a form of the spotted species, known as _H. crocuta spelaea_. Fossil hyenas occur in the Lower Pliocene of Greece, China, India, &c.; while remains indistinguishable from those of the striped species have been found in the Upper Pliocene of England and Italy.

HYÈRES, a town in the department of the Var in S.E. France, 11 m. by rail E. of Toulon. In 1906 the population of the commune was 17,790, of the town 10,464; the population of the former was more than doubled in the last decade of the 19th century. Hyères is celebrated (as is also its fashionable suburb, Costebelle, nearer the seashore) as a winter health resort. The town proper is situated about 2½ m. from the seashore, and on the south-western slope of a steep hill (669 ft., belonging to the Maurettes chain, 961 ft.), which is one of the westernmost spurs of the thickly wooded Montagnes des Maures. It is sheltered from the north-east and east winds, but is exposed to the cold north-west wind or _mistral_. Towards the south and south-east a fertile plain, once famous for its orange groves, but now mainly covered by vineyards and farms, stretches to the sea, while to the south-west, across a narrow valley, rises a cluster of low hills, on which is the suburb of Costebelle. The older portion of the town is still surrounded, on the north and east, by its ancient, though dilapidated medieval walls, and is a labyrinth of steep and dirty streets. The more modern quarter which has grown up at the southern foot of the hill has handsome broad boulevards and villas, many of them with beautiful gardens, filled with semi-tropical plants. Among the objects of interest in the old town are: the house (Rue Rabaton, 7) where J. B. Massillon (1663-1742), the famous pulpit orator, was born; the parish church of St Louis, built originally in the 13th century by the Cordelier or Franciscan friars, but completely restored in the earlier part of the 19th century; and the site of the old château, on the summit of the hill, now occupied by a villa. The plain between the new town and the sea is occupied by large nurseries, an excellent _jardin d'acclimatation_, and many market gardens, which supply Paris and London with early fruits and vegetables, especially artichokes, as well as with roses in winter. There are extensive salt beds (_salines_) both on the peninsula of Giens, S. of the town, and also E. of the town. To the east of the Giens peninsula is the fine natural harbour of Hyères, as well as three thinly populated islands (the Stoechades of the ancients), Porquerolles, Port Cros and Le Levant, which are grouped together under the common name of Îles d'Hyères.

The town of Hyères seems to have been founded in the 10th century, as a place of defence against pirates, and takes its name from the aires (_hierbo_ in the Provençal dialect), or threshing-floors for corn, which then occupied its site. It passed from the possession of the viscounts of Marseilles to Charles of Anjou, count of Provence, and brother of St Louis (the latter landed here in 1254, on his return from Egypt). The château was dismantled by Henri IV., but thanks to its walls, the town resisted in 1707 an attack made by the duke of Savoy.

See Ch. Lenthéric, _La Provence Maritime ancienne et moderne_ (chap.
5) (Paris, 1880). (W. A. B. C.)

HYGIEIA, in Greek mythology, the goddess of health. It seems probable that she was originally an abstraction, subsequently personified, rather than an independent divinity of very ancient date. The question of the original home of her worship has been much discussed. The oldest traces of it, so far as is known at present, are to be found at Titane in the territory of Sicyon, where she was worshipped together with Asclepius, to whom she appears completely assimilated, not an independent personality. Her cult was not introduced at Epidaurus till a late date, and therefore, when in 420 B.C. the worship of Asclepius was introduced at Athens coupled with that of Hygieia, it is not to be inferred that she accompanied him from Epidaurus, or that she is a Peloponnesian importation at all. It is most probable that she was invented at the time of the introduction of Asclepius, after the sufferings caused by the plague had directed special attention to sanitary matters. The already existing worship of Athena Hygieia had nothing to do with Hygieia the goddess of health, but merely denoted the recognition of the power of healing as one of the attributes of Athena, which gradually became crystallized into a concrete personality. At first no special relationship existed between Asclepius and Hygieia, but gradually she came to be regarded as his daughter, the place of his wife being already secured by Epione. Later Orphic hymns, however, and Herodas iv. 1-9, make her the wife of Asclepius. The cult of Hygieia then spread concurrently with that of Asclepius, and was introduced at Rome from Epidaurus in 293, by which time she may have been admitted (which was not the case before) into the Epidaurian family of the god. Her proper name as a Romanized Greek importation was Valetudo, but she was gradually identified with Salus, an older genuine Italian divinity, to whom a temple had already been erected in 302. While in classical times Asclepius and Hygieia are simply the god and goddess of health, in the declining years of paganism they are protecting divinities generally, who preserve mankind not only from sickness but from all dangers on land and sea. In works of art Hygieia is represented, together with Asclepius, as a maiden of benevolent appearance, wearing the chiton and giving food or drink to a serpent out of a dish.

See the article by H. Lechat in Daremberg and Saglio's _Dictionnaire
des antiquités_, with full references to authorities; and E. Thrämer
in Roscher's _Lexikon der Mythologie_, with a special section on the
modern theories of Hygieia.

HYGIENE (Fr. _hygiène_, from Gr. [Greek: hygiainein], to be healthy), the science of preserving health, its practical aim being to render "growth more perfect, decay less rapid, life more vigorous, death more remote." The subject is thus a very wide one, embracing all the agencies which affect the physical and mental well-being of man, and it requires acquaintance with such diverse sciences as physics, chemistry, geology, engineering, architecture, meteorology, epidemiology, bacteriology and statistics. On the personal or individual side it involves consideration of the character and quality of food and of water and other beverages; of clothing; of work, exercise and sleep; of personal cleanliness, of special habits, such as the use of tobacco, narcotics, &c.; and of control of sexual and other passions. In its more general and public aspects it must take cognizance of meteorological conditions, roughly included under the term climate; of the site or soil on which dwellings are placed; of the character, materials and arrangement of dwellings, whether regarded individually or in relation to other houses among which they stand; of their heating and ventilation; of the removal of excreta and other effete matters; of medical knowledge relating to the incidence and prevention of disease; and of the disposal of the dead.

These topics will be found treated in such articles as DIETETICS,
FOOD, FOOD-PRESERVATION, ADULTERATION, WATER, HEATING, VENTILATION,
SEWERAGE, BACTERIOLOGY, HOUSING, CREMATION, &c. For legal enactments
which concern the sanitary well-being of the community, see PUBLIC
HEALTH.

HYGINUS, eighth pope. It was during his pontificate (c. 137-140) that the gnostic heresies began to manifest themselves at Rome.

HYGINUS (surnamed GROMATICUS, from _gruma_, a surveyor's measuring-rod), Latin writer on land-surveying, flourished in the reign of Trajan (A.D. 98-117). Fragments of a work on legal boundaries attributed to him will be found in C. F. Lachmann, _Gromatici Veteres_, i. (1848).

A treatise on Castrametation (_De Munitionibus Castrorum_), also
attributed to him, is probably of later date, about the 3rd century
A.D. (ed. W. Gemoll, 1879; A. von Domaszewski, 1887).

HYGINUS, GAIUS JULIUS, Latin author, a native of Spain (or Alexandria), was a pupil of the famous Cornelius Alexander Polyhistor and a freedman of Augustus, by whom he was made superintendent of the Palatine library (Suetonius, _De Grammaticis_, 20). He is said to have fallen into great poverty in his old age, and to have been supported by the historian Clodius Licinus. He was a voluminous author, and his works included topographical and biographical treatises, commentaries on Helvius Cinna and the poems of Virgil, and disquisitions on agriculture and bee-keeping. All these are lost.

Under the name of Hyginus two school treatises on mythology are
extant: (1) _Fabularum Liber_, some 300 mythological legends and
celestial genealogies, valuable for the use made by the author of the
works of Greek tragedians now lost; (2) _De Astronomia_, usually
called _Poetica Astronomica_, containing an elementary treatise on
astronomy and the myths connected with the stars, chiefly based on the
[Greek: Katasterismoi] of Eratosthenes. Both are abridgments and both
are by the same hand; but the style and Latinity and the elementary
mistakes (especially in the rendering of the Greek originals) are held
to prove that they cannot have been the work of so distinguished a
scholar as C. Julius Hyginus. It is suggested that these treatises are
an abridgment (made in the latter half of the 2nd century) of the
_Genealogiae_ of Hyginus by an unknown grammarian, who added a
complete treatise on mythology.

EDITIONS.--_Fabulae_, by M. Schmidt (1872); _De Astronomia_, by B.
Bunte (1875); see also Bunte, _De C. Julii Hygini, Augusti Liberti,
Vita et Scriptis_ (1846).

HYGROMETER (Gr. [Greek: hygros], moist, [Greek: metron], a measure), an instrument for measuring the absolute or relative amount of moisture in the atmosphere; an instrument which only qualitatively determines changes in the humidity is termed a "hygroscope." The earlier instruments generally depended for their action on the contraction or extension of substances when exposed to varying degrees of moisture; catgut, hair, twisted cords and wooden laths, all of which contract with an increase in the humidity and vice versa, being the most favoured materials. The familiar "weather house" exemplifies this property. This toy consists of a house provided with two doors, through which either a man or woman appears according as the weather is about to be wet or fine. This action is effected by fixing a catgut thread to the base on which the figures are mounted, in such a manner that contraction of the thread rotates the figures so that the man appears and extension so that the woman appears.

Many of the early forms are described in C. Hutton, _Math. and Phil.
Dictionary_ (1815). The modern instruments, which utilize other
principles, are described in METEOROLOGY: II. _Methods and Apparatus_.

HYKSOS, or "SHEPHERD KINGS," the name of the earliest invaders of Egypt of whom we have definite evidence in tradition. Josephus (c. _Apion._ i. 14), who identifies the Hyksos with the Israelites, preserves a passage from the second book of Manetho giving an account of them. (It may be that Josephus had it, not direct from Manetho's writings, but through the garbled version of some Alexandrine compiler.) In outline it is as follows. In the days of a king of Egypt named Timaeus the land was suddenly invaded from the east by men of ignoble race, who conquered it without a struggle, destroyed cities and temples, and slew or enslaved the inhabitants. At length they elected a king named Salatis, who, residing at Memphis, made all Egypt tributary, and established garrisons in different parts, especially eastwards, fearing the Assyrians. He built also a great fortress at Avaris, in the Sethroite nome, east of the Bubastite branch of the Nile. Salatis was followed in succession by Beon, Apachnas, Apophis, Jannas and Asses. These six kings reigned 198 years and 10 months, and all aimed at extirpating the Egyptians. Their whole race was named Hyksos, i.e. "shepherd kings," and some say they were Arabs (another explanation found by Josephus is "captive shepherds"). When they and their successors had held Egypt for 511 years, the kings of the Thebais and other parts of Egypt rebelled, and a long and mighty war began. Misphragmuthosis worsted the "Shepherds" and shut them up in Avaris; and his son Thutmosis, failing to capture the stronghold, allowed them to depart; whereupon they went forth, 240,000 in number, established themselves in Judea and built Jerusalem.

In Manetho's list of kings, the six above named (with many variations in detail) form the XVth dynasty, and are called "six foreign Phoenician kings." The XVIth dynasty is of thirty-two "Hellenic (_sic?_) shepherd kings," the seventeenth is of "shepherds and Theban kings" (reigning simultaneously). The lists vary greatly in different versions, but the above seems the most reasonable selection of readings to be made. For "Hellenic" see below. The supposed connexion with the Israelites has made the problem of the Hyksos attractive, but light is coming upon it very slowly. In 1847 E. de Rougé proved from a fragment of a story in the papyri of the British Museum, that Apopi was one of the latest of the Hyksos kings, corresponding to Aphobis; he was king of the "pest" and suppressed the worship of the Egyptian gods, and endeavoured to make the Egyptians worship his god Setekh or Seti; at the same time an Egyptian named Seqenenre reigned in Thebes, more or less subject to Aphobis. The city of Hawari (Avaris) was also mentioned in the fragment.

In 1850 a record of the capture of this city from the Hyksos by Ahmosi, the founder of the eighteenth dynasty, was discovered by the same scholar. A large class of monuments was afterwards attributed to the Hyksos, probably in error. Some statues and sphinxes, found in 1861 by Mariette at Tanis (in the north-east of the Delta), which had been usurped by later kings, had peculiar "un-Egyptian" features. One of these bore the name of Apopi engraved lightly on the shoulder; this was evidently a usurper's mark, but from the whole circumstances it was concluded that these, and others of the same type of features found elsewhere, must have belonged to the Hyksos. This view held the field until 1893, when Golénischeff produced an inferior example bearing its original name, which showed that in this case it represented Amenemhe III. In consequence it is now generally believed that they all belong to the twelfth dynasty. Meanwhile a headless statue of a king named Khyan, found at Bubastis, was attributed on various grounds to the Hyksos, the soundest arguments being his foreign name and the boastful un-Egyptian epithet "beloved of his _ka_," where "beloved of Ptah" or some other god was to be expected. His name was immediately afterwards recognized on a lion found as far away from Egypt as Bagdad. Flinders Petrie then pointed out a group of kings named on scarabs of peculiar type, which, including Khyan, he attributed to the period between the Old Kingdom and the New, while others were in favour of assigning them all to the Hyksos, whose appellation seemed to be recognizable in the title Hek-khos, "ruler of the barbarians," borne by Khyan. The extraordinary importance of Khyan was further shown by the discovery of his name on a jar-lid at Cnossus in Crete. Semitic features were pointed out in the supposed Hyksos names, and Petrie was convinced of their date by his excavations of 1905-1906 in the eastern Delta. Avaris is generally assigned to the region towards Pelusium on the strength of its being located in the Sethroite nome by Josephus, but Petrie thinks it was at Tell el-Yahudiyeh (Yehudia), where Hyksos scarabs are common. From the remains of fortifications there he argues that the Hyksos were uncivilized desert people, skilled in the use of the bow, and must thus have destroyed by their archery the Egyptian armies trained to fight hand-to-hand; further, that their hordes were centered in Syria, but were driven thence by a superior force in the East to take refuge in the islands and became a sea-power--whence the strange description "Hellenic" in Manetho, which most editors have corrected to [Greek: alloi], "others." Besides the statue of Khyan, blocks of granite with the name of Apopi have been found in Upper Egypt at Gebelen and in Lower Egypt at Bubastis. The celebrated Rhind mathematical papyrus was copied in the reign of an Apopi from an original of the time of Amenemhe III. Large numbers of Hyksos scarabs are found in Upper and Lower Egypt, and they are not unknown in Palestine. Khyan's monuments, inconspicuous as they are, actually extend over a wider area--from Bagdad to Cnossus--than those of any other Egyptian king.

It is certain that this mysterious people were Asiatic, for they are called so by the Egyptians. Though Seth was an Egyptian god, as god of the Hyksos he represents some Asiatic deity. The possibility of a connexion between the Hyksos and the Israelites is still admitted in some quarters. Hatred of these impious foreigners, of which there is some trace in more than one text, aroused amongst the Egyptians (as nothing ever did before or since) that martial spirit which carried the armies of Tethmosis to the Euphrates.

Besides the histories of Egypt, see J. H. Breasted, _Ancient Records
of Egypt_; Historical Documents ii. 4, 125; G. Maspero, _Contes
populaires_, 3me éd. p. 236; W. M. F. Petrie, _Hyksos and Israelite
Cities_, p. 67; Golénischeff in _Recueil de travaux_, xv. p. 131.
(F. Ll. G.)

HYLAS, In Greek legend, son of Theiodamas, king of the Dryopians in Thessaly, the favourite of Heracles and his companion on the Argonautic expedition. Having gone ashore at Kios in Mysia to fetch water, he was carried off by the nymphs of the spring in which he dipped his pitcher. Heracles sought him in vain, and the answer of Hylas to his thrice-repeated cry was lost in the depths of the water. Ever afterwards, in memory of the threat of Heracles to ravage the land if Hylas were not found, the inhabitants of Kios every year on a stated day roamed the mountains, shouting aloud for Hylas (Apollonius Rhodius i. 1207; Theocritus xiii.; Strabo xii. 564; Propertius i. 20; Virgil, _Ecl._ vi. 43). But, although the legend is first told in Alexandrian times, the "cry of Hylas" occurs long before as the "Mysian cry" in Aeschylus (_Persae_, 1054), and in Aristophanes (_Plutus_, 1127) "to cry Hylas" is used proverbially of seeking something in vain. Hylas, like Adonis and Hyacinthus, represents the fresh vegetation of spring, or the water of a fountain, which dries up under the heat of summer. It is suggested that Hylas was a harvest deity and that the ceremony gone through by the Kians was a harvest festival, at which the figure of a boy was thrown into the water, signifying the dying vegetation-spirit of the year.

See G. Türk in _Breslauer Philologische Abhandlungen_, vii. (1895); W.
Mannhardt, _Mythologische Forschungen_ (1884).

HYLOZOISM (Gr. [Greek: hylê], matter, [Greek: zôê], life), in philosophy, a term applied to any system which explains all life, whether physical or mental, as ultimately derived from matter ("cosmic matter," _Weldstoff_). Such a view of existence has been common throughout the history of thought, and especially among physical scientists. Thus the Ionian school of philosophy, which began with Thales, sought for the beginning of all things in various material substances, water, air, fire (see IONIAN SCHOOL). These substances were regarded as being in some sense alive, and taking some active part in the development of being. This primitive hylozoism reappeared in modified forms in medieval and Renaissance thought, and in modern times the doctrine of materialistic monism is its representative. Between modern materialism and hylozoism proper there is, however, the distinction that the ancients, however vaguely, conceived the elemental matter as being in some sense animate if not actually conscious and conative.

HYMEN, or HYMENAEUS, originally the name of the song sung at marriages among the Greeks. As usual the name gradually produced the idea of an actual person whose adventures gave rise to the custom of this song. He occurs often in association with Linus and Ialemus, who represent similar personifications, and is generally called a son of Apollo and a Muse. As the son of Dionysus and Aphrodite, he was regarded as a god of fruitfulness. In Attic legend he was a beautiful youth who, being in love with a girl, followed her in a procession to Eleusis disguised as a woman, and saved the whole band from pirates. As reward he obtained the girl in marriage, and his happy married life caused him ever afterwards to be invoked in marriage songs (Servius on Virgil, _Aen._ i. 651). According to another story, he was a youth who was killed by the fall of his house on his wedding day; hence he was invoked, to propitiate him and avert a similar fate from others (Servius, loc. cit.). He is represented in works of art as an effeminate-looking, winged youth, carrying a bridal torch and wearing a nuptial veil. The marriage song was sung, with musical accompaniment, during the procession of the bride from her parents' house to that of the bridegroom, Hymenaeus being invoked at the end of each portion.

See R. Schmidt, _De Hymenaeo el Talasio_ (1886), and J. A. Hild in
Daremberg and Saglis's _Dictionnaire des antiquités_.

HYMENOPTERA (Gr. [Greek: hymên], a membrane, and [Greek: pteron], a wing), a term used in zoological classification for one of the most important orders of the class _Hexapoda_ (q.v.). The order was founded by Linnaeus (_Systema Naturae_, 1735), and is still recognized by all naturalists in the sense proposed by him, to include the saw-flies, gall-flies, ichneumon-flies and their allies, ants, wasps and bees. The relationship of the Hymenoptera to other orders of insects is discussed in the article HEXAPODA, but it may be mentioned here that in structure the highest members of the order are remarkably specialized, and that in the perfection of their instincts they stand at the head of all insects and indeed of all invertebrate animals. About 30,000 species of Hymenoptera are now known.

FIG. 1.--A, Front of head of Saw-fly (_Pachynematus_); a, labrum; b, clypeus; c, vertex; d, d, antennal cavities. C and D, Mandibles. E, First maxilla; a, cardo; b, stipes; c, galea; d, lacinia; e, palp. B, Second maxillae (Labium); a, mentum; b, ligula (between the two galeae); c, c, palps. Magnified.]

FIG. 3.--Median section through mid-body of female Red Ant (_Myrmica rubra_). H, Head; 1, 2, 3, the thoracic segments; i., ii., the first and second abdominal segments; i., being the propodeum.]