ENTHUSIASM

enthusiasm, a word originally meaning inspiration by a divine afflatus or by the presence of a god. the gr. [greek: enthousiasmos], from which the word is adapted, is formed from the verb [greek: enthousiazein], to be [greek: entheos], possessed by a god [greek: theos]. applied by the greeks to manifestations of divine "possession," by apollo, as in the case of the pythia, or by dionysus, as in the case of the bacchantes and maenads, it was also used in a transferred or figurative sense; thus socrates speaks of the inspiration of poets as a form of enthusiasm (plato, _apol. soc._ 22 c). its uses, in a religious sense, are confined to an exaggerated or wrongful belief in religious inspiration, or to intense religious fervour or emotion. thus a syrian sect of the 4th century was known as "the enthusiasts"; they believed that by perpetual prayer, ascetic practices and contemplation, man could become inspired by the holy spirit, in spite of the ruling evil spirit, which the fall had given to him. from their belief in the efficacy of prayer [greek: euche], they were also known as euchites. in ordinary usage, "enthusiasm" has lost its peculiar religious significance, and means a whole-hearted devotion to an ideal, cause, study or pursuit; sometimes, in a depreciatory sense, it implies a devotion which is partisan and is blind to difficulties and objections. (see further inspiration, for a comparison of the religious meanings of "enthusiasm," "ecstasy" and "fanaticism.") enthymeme (gr. [greek: en, thymos]), in formal logic, the technical name of a syllogistic argument which is incompletely stated. any one of the premises may be omitted, but in general it is that one which is most obvious or most naturally present to the mind. in point of fact the full formal statement of a syllogism is rare, especially in rhetorical language, when the deliberate omission of one of the premises has a dramatic effect. thus the suppression of the conclusion may have the effect of emphasizing the idea which necessarily follows from the premises. far commoner is the omission of one of the premises which is either too clear to need statement or of a character which makes its omission desirable. a famous instance quoted in the _port royal logic_, pt. iii. ch. xiv., is medea's remark to jason in ovid's _medea_, "servare potui, perdere an possim rogas?" where the major premise "qui servare, perdere possunt" is understood. this use of the word enthymeme differs from aristotle's original application of it to a syllogism based on probabilities or signs ([greek: ex eikoton e semeion]), i.e. on propositions which are generally valid ([greek: eikota]) or on particular facts which may be held to justify a general principle or another particular fact (_anal. prior._ [beta] xxvii. 70 a 10). see beside text-books on logic, sir w. hamilton's _discussions_ (1547); mansel's ed. of aldrich, appendix f; h.w.b. joseph, _introd. to logic_, chap. xvi. entomology (gr. [greek: entoma,] insects, and [greek: logos], a discourse), the science that treats of insects, i.e. of the animals included in the class hexapoda of the great phylum (or sub-phylum) arthropoda. the term, however, is somewhat elastic in its current use, and students of centipedes and spiders are often reckoned among the entomologists. as the number of species of insects is believed to exceed that of all other animals taken together, it is no wonder that their study should form a special division of zoology with a distinctive name. beetles (scarabaei) are the subjects of some of the oldest sculptured works of the egyptians, and references to locusts, bees and ants are familiar to all readers of the hebrew scriptures. the interest of insects to the eastern races was, however, economic, religious or moral. the science of insects began with aristotle, who included in a class "entoma" the true insects, the arachnids and the myriapods, the crustacea forming another class ("malacostraca") of the "anaema" or "bloodless animals." for nearly 2000 years the few writers who dealt with zoological subjects followed aristotle's leading. in the history of the science, various lines of progress have to be traced. while some observers have studied in detail the structure and life-history of a few selected types (insect anatomy and development), others have made a more superficial examination of large series of insects to classify them and determine their relationships (systematic entomology), while others again have investigated the habits and life-relations of insects (insect bionomics). during recent years the study of fossil insects (palaeoentomology) has attracted much attention. the foundations of modern entomology were laid by a series of wonderful memoirs on anatomy and development published in the 17th and 18th centuries. of these the most famous are m. malpighi's treatise on the silkworm (1669) and j. swammerdam's _biblia naturae_, issued in 1737, fifty years after its author's death, and containing observations on the structure and life-history of a series of insect types. aristotle and harvey (_de generatione animalium_, 1651) had considered the insect larva as a prematurely hatched embryo and the pupa as a second egg. swammerdam, however, showed the presence under the larval cuticle of the pupal structures. his only unfortunate contribution to entomology--indeed to zoology generally--was his theory of pre-formation, which taught the presence within the egg of a perfectly formed but miniature adult. a year before malpighi's great work appeared, another italian naturalist, f. redi, had disproved by experiment the spontaneous generation of maggots from putrid flesh, and had shown that they can only develop from the eggs of flies. meanwhile the english naturalist, john ray, was studying the classification of animals; he published, in 1705, his _methodus insectorum_, in which the nature of the metamorphosis received due weight. ray's "insects" comprised the arachnids, crustacea, myriapoda and annelida, in addition to the hexapods. ray was the first to formulate that definite conception of the species which was adopted by linnaeus and emphasized by his binominal nomenclature. in 1735 appeared the first edition of the _systema naturae_ of linnaeus, in which the "insecta" form a group equivalent to the arthropoda of modern zoologists, and are divided into seven orders, whose names--coleoptera, diptera, lepidoptera, &c., founded on the nature of the wings--have become firmly established. the fascinating subjects of insect bionomics and life-history were dealt with in the classical memoirs (1734-1742) of the frenchman r.a.f. de reaumur, and (1752-1778) of the swede c. de geer. the freshness, the air of leisure, the enthusiasm of discovery that mark the work of these old writers have lessons for the modern professional zoologist, who at times feels burdened with the accumulated knowledge of a century and a half. from the end of the 18th century until the present day, it is only possible to enumerate the outstanding features in the progress of entomology. in the realm of classification, the work of linnaeus was continued in denmark by j.c. fabricius (_systema entomologica_, 1775), and extended in france by g.p.b. lamarck (_animaux sans vertebres_, 1801) and g. cuvier (_lecons d'anatomie comparee_, 1800-1805), and in england by w.e. leach (_trans. linn. soc._ xi., 1815). these three authors definitely separated the arachnida, crustacea and myriapoda as classes distinct from the insecta (see hexapoda). the work of j.o. westwood (_modern classification of insects_, 1839-1840) connects these older writers with their successors of to-day. in the anatomical field the work of malpighi and swammerdam was at first continued most energetically by french students. p. lyonnet had published in 1760 his elaborate monograph on the goat-moth caterpillar, and h.e. strauss-durckheim in 1828 issued his great treatise on the cockchafer. but the name of j.c.l. de savigny, who (_mem. sur les animaux sans vertebres_, 1816) established the homology of the jaws of all insects whether biting or sucking, deserves especial honour. many anatomical and developmental details were carefully worked out by l. dufour (in a long series of memoirs from 1811 to 1860) in france, by g. newport ("insecta" in _encyc. anat. and physiol._, 1839) in england, and by h. burmeister (_handbuch der entomologie_, 1832) in germany. through the 19th century, as knowledge increased, the work of investigation became necessarily more and more specialized. anatomists like f. leydig, f. muller, b.t. lowne and v. graber turned their attention to the detailed investigation of some one species or to special points in the structure of some particular organs, using for the elucidation of their subject the ever-improving microscopical methods of research. societies for the discussion and publication of papers on entomology were naturally established as the number of students increased. the societe entomologique de france was founded in 1832, the entomological society of london in 1834. few branches of zoology have been more valuable as a meeting-ground for professional and amateur naturalists than entomology, and not seldom has the amateur--as in the case of westwood--developed into a professor. during the pre-linnaean period, the beauty of insects--especially the lepidoptera--had attracted a number of collectors; and these "aurelians"--regarded as harmless lunatics by most of their friends--were the forerunners of the systematic students of later times. while the insect fauna of european countries was investigated by local naturalists, the spread of geographical exploration brought ever-increasing stores of exotic material to the great museums, and specialization--either in the fauna of a small district or in the world-wide study of an order or a group of families--became constantly more marked in systematic work. as examples may be instanced the studies of a.h. haliday and h. loew on the european diptera, of john curtis on british insects, of h.t. stainton and o. staudinger on the european lepidoptera, of r. m'lachlan on the european and of h.a. hagen on the north american neuroptera, of d. sharp on the _dyticidae_ and other families of coleoptera of the whole world. the embryology of insects is entirely a study of the last century. c. bonnet indeed observed in 1745 the virgin-reproduction of aphids, but it was not until 1842 that r.a. von kolliker described the formation of the blastoderm in the egg of the midge _chironomus_. later a. weismann (1863-1864) traced details of the growth of embryo and of pupa among the diptera, and a. kovalevsky in 1871 first described the formation of the germinal layers in insects. most of the recent work on the embryology of insects has been done in germany or the united states, and among numerous students v. graber, k. heider, w.m. wheeler and r. heymons may be especially mentioned. the work of de reaumur and de geer on the bionomics and life-history of insects has been continued by numerous observers, among whom may be especially mentioned in france j.h. fabre and c. janet, in england w. kirby and w. spence, j. lubbock (lord avebury) and l.c. miall, and in the united states c.v. riley. the last-named may be considered the founder of the strong company of entomological workers now labouring in america. though riley was especially interested in the bearings of insect life on agriculture and industry--economic entomology (q.v.)--he and his followers have laid the science generally under a deep obligation by their researches. after the publication of c. darwin's _origin of species_ (1859) a fresh impetus was given to entomology as to all branches of zoology, and it became generally recognized that insects form a group convenient and hopeful for the elucidation of certain problems of animal evolution. the writings of darwin himself and of a.r. wallace (both at one time active entomological collectors) contain much evidence drawn from insects in favour of descent with modification. the phylogeny of insects has since been discussed by f. brauer, a.s. packard and many others; mimicry and allied problems by h.w. bates, f. muller, e.b. poulton and m.c. piepers; the bearing of insect habits on theories of selection and use-inheritance by a. weismann, g.w. and e. peckham, g.h.t. eimer and herbert spencer; variation by w. bateson and m. standfuss. bibliography.--references to the works of the above authors, and to many others, will be found under hexapoda and the special articles on various insect orders. valuable summaries of the labours of malpighi, swammerdam and other early entomologists are given in l.c. miall and a. denny's _cockroach_ (london, 1886), and l. henneguy's _les insectes_ (paris, 1904). (g. h. c.) entomostraca. this zoological term, as now restricted, includes the branchiopoda, ostracoda and copepoda. the ostracoda have the body enclosed in a bivalve shell-covering, and normally unsegmented. the branchiopoda have a very variable number of body-segments, with or without a shield, simple or bivalved, and some of the postoral appendages normally branchial. the copepoda have normally a segmented body, not enclosed in a bivalved shell-covering, the segments not exceeding eleven, the limbs not branchial. under the heading crustacea the entomostraca have already been distinguished not only from the thyrostraca or cirripedes, but also from the malacostraca, and an intermediate group of which the true position is still disputed. the choice is open to maintain the last as an independent subclass, and to follow claus in calling it the leptostraca, or to introduce it among the malacostraca as the nebaliacea, or with packard and sars to make it an entomostracan subdivision under the title phyllocarida. at present it comprises the single family _nebaliidae_. the bivalved carapace has a jointed rostrum, and covers only the front part of the body, to which it is only attached quite in front, the valve-like sides being under control of an adductor muscle. the eyes are stalked and movable. the first antennae have a lamellar appendage at the end of the peduncle, a decidedly non-entomostracan feature. the second antennae, mandibles and two pairs of maxillae may also be claimed as of malacostracan type. to these succeed eight pairs of foliaceous branchial appendages on the front division of the body, followed on the hind division by four pairs of powerful bifurcate swimming feet and two rudimentary pairs, the number, though not the nature, of these appendages being malacostracan. on the other hand, the two limbless segments that precede the caudal furca are decidedly non-malacostracan. the family was long limited to the single genus _nebalia_ (leach), and the single species _n. bipes_ (o. fabricius). recently sars has added a norwegian species, _n. typhlops_, not blind but weak-eyed. there are also now two more genera, _paranebalia_ (claus, 1880), in which the branchial feet are much longer than in _nebalia_, and _nebaliopsis_ (sars, 1887), in which they are much shorter. all the species are marine. branchiopoda.--in this order, exclusion of the phyllocarida will leave three suborders of very unequal extent, the phyllopoda, cladocera, branchiura. the constituents of the last have often been classed as copepoda, and among the branchiopods must be regarded as aberrant, since the "branchial tail" implied in the name has no feet, and the actual feet are by no means obviously branchial. _phyllopoda._--this "leaf-footed" suborder has the appendages which follow the second maxillae variable in number, but all foliaceous and branchial. the development begins with a free nauplius stage. in the outward appearance of the adults there is great want of uniformity, one set having their limbs sheltered by no carapace, another having a broad shield over most of them, and a third having a bivalved shell-cover within which the whole body can be enclosed. in accord with these differences the sections may be named gymnophylla, notophylla, conchophylla. the equivalent terms applied by sars are anostraca, notostraca, conchostraca, involving a termination already appropriated to higher divisions of the crustacean class, for which it ought to be reserved. 1. gymnophylla.--these singular crustaceans have long soft flexible bodies, the eyes stalked and movable, the first antennae small and filiform, the second lamellar in the female, in the male prehensile; this last character gives rise to some very fanciful developments. there are three families, two of which form companies rather severely limited. thus the _polyartemiidae_, which compensate themselves for their stumpy little tails by having nineteen instead of the normal eleven pairs of branchial feet, consist exclusively of _polyartemia forcipata_ (fischer, 1851). this species from the high north of europe and asia carries green eggs, and above them a bright pattern in ultramarine (sars, 1896, 1897). the _thamnocephalidae_ have likewise but a single species, _thamnocephalus platyurus_ (packard, 1877), which justifies its title "bushy-head of the broad tail" by a singularity at each end. forward from the head extends a long ramified appendage described as the "frontal shrub," backward from the fourth abdominal segment of the male spreads a fin-like expansion which is unique. in the ravines of kansas, pools supplied by torrential rains give birth to these and many other phyllopods, and in turn "millions of them perish by the drying up of the pools in july" (packard). the remaining family, the _branchipodidae_, includes eight genera. in the long familiar _branchipus_, _chirocephalus_ and _streptocephalus_ the males have frontal appendages, but these are wanting in the "brine-shrimp" _artemia_, and the same want helps to distinguish _branchinecta_ (verrill, 1869) from the old genus _branchipus_. of _branchiopsyllus_ (sars, 1897) the male is not yet known, but in his genera of the same date, the siberian _artemiopsis_ and the south african _branchipodopsis_ (1898), there is no such appendage. of the last genus the type species _b. hodgsoni_ belongs to cape colony, but the specimens described were born and bred and observed in norway. for the study of fresh-water entomostraca large possibilities are now opened to the naturalist. a parcel of dried mud, coming for example from palestine or queensland, and after an indefinite interval of time put into water in england or elsewhere, may yield him living forms, both new and old, in the most agreeable variety. some caution should be used against confounding accidentally introduced indigenous species with those reared from the imported eggs. those, too, who send or bring the foreign soil should exercise a little thought in the choice of it, since dry earth that has never had any entomostraca near it at home will not become fertile in them by the mere fact of exportation. 2. notophylla.--in this division the body is partly covered by a broad shield, united in front with the head; the eyes are sessile, the first antennae are small, the second rudimentary or wanting; of the numerous feet, sometimes sixty-three pairs, exceeding the number of segments to which they are attached, the first pair are more or less unlike the rest, and in the female the eleventh have the epipod and exopod (flabellum and sub-apical lobe of lankester) modified to form an ovisac. development begins with a nauplius stage. males are very rare. the single family _apodidae_ contains only two genera, _apus_ and its very near neighbour _lepidurus_. _apus australiensis_ (spencer and hall, 1896) may rank as the largest of the entomostraca, reaching in the male, from front of shield to end of telson, a length of 70 mm., in the female of 64 mm. in a few days, or at most a fortnight, after a rainfall numberless specimens of these sizes were found swimming about, "and as not a single one was to be found in the water-pools prior to the rain, these must have been developed from the egg." similarly, in northern india _apus himalayanus_ was "collected from a stagnant pool in a jungle four days after a shower of rain had fallen," following a drought of four months (packard). 3. conchophylla.--though concealed within the bivalved shell-cover, the mouth-parts are nearly as in the gymnophylla, but the flexing of the caudal part is in contrast, and the biramous second antennae correspond with what is only a larval character in the other phyllopods. in the male the first one or two pairs of feet are modified into grasping organs. the small ova are crowded beneath the dorsal part of the valves. the development usually begins with a nauplius stage (sars, 1896, 1900). there are four families: (a) the _limnadiidae_, with feet from 18 to 32 pairs, comprise four (or five) genera. of these _limnadella_ (girard, 1855) has a single eye. it remains rather obscure, though the type species originally "was discovered in great abundance in a roadside puddle subject to desiccation." _limnadia_ (brongniart, 1820) is supposed to consist of species exclusively parthenogenetic. but when asked to believe that males never occur among these amazons, one cannot but remember how hard it is to prove a negative. (b) the _lynceidae_, with not more than twelve pairs of feet. this family is limited to the species, widely distributed, of the single genus _lynceus_, established by o.f. muller in 1776 and 1781, and first restricted by leach in 1816 in the _encyclopaedia britannica_ (art. "annulosa," of that edition). leach there assigns to it the single species _l. brachyurus_ (muller), and as this is included in the genus _limnetis_ (loven, 1846), that genus must be a synonym of _lynceus_ as restricted. (c) _leptestheriidae_. _estheria_ (ruppell, 1837) was instituted for the species _dahalacensis_, which sars includes in his genus _leptestheria_ (1898); but _estheria_ was already appropriated, and of its synonyms _cyzicus_ (audouin, 1837) is lost for vagueness, while _isaura_ (joly, 1842) is also appropriated, so that _leptestheria_ becomes the name of the typical genus, and determines the name of the family. (d) _cyclestheriidae_. this family consists of the single species _cyclestheria hislopi_ (baird), reported from india, ceylon, celebes, australia, east africa and brazil. sars (1887) having had the opportunity of raising it from dried australian mud, found that, unlike other phyllopods, but like the cladocera, the parent keeps its brood within the shell until their full development. _cladocera._--in this suborder the head is more or less distinct, the rest of the body being in general laterally compressed and covered by a bivalved test. the title "branching horns" alludes to the second antennae, which are two-branched except in the females of _holopedium_, with each branch setiferous, composed of only two to four joints. the mandibles are without palp. the pairs of feet are four to six. the eye is single, and in addition to the eye there is often an "eye-spot," _monospilus_ being unique in having the eye-spot alone and no eye, while _leydigiopsis_ (sars, 1901) has an eye with an eye-spot equal to it or larger. the heart has a pair of venous ostia, often blending into one, and an anterior arterial aorta. respiration is conducted by the general surface, by the branchial lamina (external branch) of the feet, and the vesicular appendage (when present) at the base of this branch. the "abdomen," behind the limbs, is usually very short, occasionally very long. the "postabdomen," marked off by the two postabdominal setae, usually has teeth or spines, and ends in two denticulate or ciliate claws, or it may be rudimentary, as in _polyphemus_. many species have a special glandular organ at the back of the head, which _sida crystallina_ uses for attaching itself to various objects. the leydigian or nuchal organ is supposed to be auditory and to contain an otolith. the female lays two kinds of eggs--"summer-eggs," which develop without fertilization, and "winter-eggs" or resting eggs, which require to be fertilized. the latter in the _daphniidae_ are enclosed in a modified part of the mother's shell, called the ephippium from its resemblance to a saddle in shape and position. in other families a less elaborate case has been observed, for which scourfield has proposed the term protoephippium. in _leydigia_ he has recently found a structure almost as complex as that of the _daphniidae_. in some families the resting eggs escape into the water without special covering. only the embryos of _leptodora_ are known to hatch out in the nauplius stage. _penilia_ (dana, 1849) is perhaps the only exclusively marine genus. the great majority of the cladocera belong to fresh water, but their adaptability is large, since _moina rectirostris_ (o.f. muller) can equally enjoy a pond at blackheath, and near odessa live in water twice as salt as that of the ocean. in point of size a cladoceran of 5 mm. is spoken of as colossal. dr jules richard in his revision (1895) retains the sections proposed by sars in 1865, calyptomera and gymnomera. the former, with the feet for the most part concealed by the carapace, is subdivided into two tribes, the ctenopoda, or "comb-feet," in which the six pairs of similar feet, all branchial and nonprehensile, are furnished with setae arranged like the teeth of a comb, and the anomopoda, or "variety-feet," in which the front feet differ from the rest by being more or less prehensile, without branchial laminae. the ctenopoda comprise two families: (a) the _holopediidae_, with a solitary species, _holopedium gibberum_ (zaddach), queerly clothed in a large gelatinous involucre, and found in mountain tarns all over europe, in large lakes of n. america, and also in shallow ponds and waters at sea-level; (b) the _sididae_, with no such involucre, but with seven genera, and rather more than twice as many species. of _diaphanosoma modiglianii_ richard says that at different points of lake toba in sumatra millions of specimens were obtained, among which he had not met with a single male. the anomopoda are arranged in four families, all but one very extensive. (a) _daphniidae_. of the seven genera, the cosmopolitan _daphnia_ contains about 100 species and varieties, of which thomas scott (1899) observes that "scarcely any of the several characters that have at one time or another been selected as affording a means for discriminating between the different forms can be relied on as satisfactory." though this may dishearten the systematist, scourfield (1900) reminds us that "it was in a water-flea that metschnikoff first saw the leucocytes (or phagocytes) trying to get rid of disease germs by swallowing them, and was so led to his epoch-making discovery of the part played by these minute amoeboid corpuscles in the animal body." for _scapholeberis mucronata_ (o.f. muller), scourfield has shown how it is adapted for movement back downwards in the water along the underside of the surface film, which to many small crustaceans is a dangerously disabling trap. (b) _bosminidae_. to _bosmina_ (baird, 1845) richard added _bosminopsis_ in 1895. (c) _macrotrichidae._ in this family _macrothrix_ (baird, 1843) is the earliest genus, among the latest being _grimaldina_ (richard, 1892) and _jheringula_ (sars, 1900). dried mud and vegetable debris from s. paulo in brazil supplied sars with representatives of all the three in his norwegian aquaria, in some of which the little _macrothrix elegans_ "multiplied to such an extraordinary extent as at last to fill up the water with immense shoals of individuals." "the appearance of male specimens was always contemporary with the first ephippial formation in the females." for _streblocerus pygmaeus_, grown under the same conditions, sars observes: "this is perhaps the smallest of the cladocera known, and is hardly more than visible to the naked eye," the adult female scarcely exceeding 0.25 mm. yet in the next family _alonella nana_ (baird) disputes the palm and claims to be the smallest of all known arthropoda. (d) _chydoridae._ this family, so commonly called _lynceidae_, contains a large number of genera, among which one may usually search in vain, and rightly so, for the genus _lynceus_. the key to the riddle is to be found in the _encyclopaedia britannica_ for 1816. there, as above explained, leach began the subdivision of muller's too comprehensive genus, the result being that _lynceus_ belongs to the phyllopoda, and _chydorus_ (leach, 1816) properly gives its name to the present family, in which the doubly convoluted intestine is so remarkable. of its many genera, _leydigia_, _leydigiopsis_, _monospilus_ have been already mentioned. _dadaya macrops_ (sars, 1901), from south america and ceylon, has a very large eye and an eye-spot fully as large, but it is a very small creature, odd in its behaviour, moving by jumps at the very surface of the water. "to the naked eye it looked like a little black atom darting about in a most wonderful manner." [illustration: fig. 1.--_dolops ranarum_ (stuhlmann).] the gymnomera, with a carapace too small to cover the feet, which are all prehensile, are divided also into two tribes, the onychopoda, in which the four pairs of feet have a toothed maxillary process at the base, and the haplopoda, in which there are six pairs of feet, without such a process. to the _polyphemidae_, the well-known family of the former tribe, sars in 1897 added two remarkable genera, _cercopagis_, meaning "tail with a sling," and _apagis_, "without a sling," for seven species from the sea of azov. the haplopoda likewise have but a single family, the _leptodoridae_, and this has but the single genus _leptodora_ (lilljeborg, 1861). dr richard (1895, 1896) gives a cladoceran bibliography of 601 references. _branchiura._--this term was introduced by thorell in 1864 for the _argulidae_, a family which had been transferred to the branchiopoda by zenker in 1854, though sometimes before and since united with the parasitic copepoda. though the animals have an oral siphon, they do not carry ovisacs like the siphonostomous copepods, but glue their eggs in rows to extraneous objects. their lateral, compound, feebly movable eyes agree with those of the phyllopoda. the family are described by claus as "intermittent parasites," because when gorged they leave their hosts, fishes or frogs, and swim about in freedom for a considerable period. the long-known _argulus_ (o.f. muller) has the second maxillae transformed into suckers, but in _dolops_ (audouin, 1837) (fig. 1), the name of which supersedes the more familiar _gyropeltis_ (heller, 1857), these effect attachment by ending in strong hooks (bouvier, 1897). a third genus, _chonopeltis_ (thiele, 1900), has suckers, but has lost its first antennae, at least in the female. ostracoda.--the body, seldom in any way segmented, is wholly encased in a bivalved shell, the caudal part strongly inflexed, and almost always ending in a furca. the limbs, including antennae and mouth organs, never exceed seven definite pairs. the first antennae never have more than eight joints. the young usually pass through several stages of development after leaving the egg, and this commonly after, even long after, the egg has left the maternal shell. parthenogenesis is frequent. the four tribes instituted by sars in 1865 were reduced to two by g.w. muller in 1894, the myodocopa, which almost always have a heart, and the podocopa, which have none. _myodocopa._--these have the furcal branches broad, lamellar, with at least three pairs of strong spines or ungues. almost always the shell has a rostral sinus. muller divides the tribe into three families, _cypridinidae, halocypridae_, and the heartless _polycopidae_, which constituted the tribe cladocopa of sars. from the first of these brady and norman distinguish the asteropidae (fig. 3), remarkable for seven pairs of long branchial leaves which fold over the hinder extremity of the animal, and the _sarsiellidae_, still somewhat obscure, besides adding the _rutidermatidae_, knowledge of which is based on skilful maceration of minute and long-dried specimens. the _halocypridae_ are destitute of compound lateral eyes, and have the sexual orifice unsymmetrically placed. _podocopa._--in these the furcal branches are linear or rudimentary, the shell is without rostral sinus, and, besides distinguishing characters of the second antennae, they have always a branchial plate well developed on the first maxillae, which is inconstant in the other tribe. there are five families: (a) _cyprididae_ (? including _cypridopsidae_ of brady and norman). in some of the genera parthenogenetic propagation is carried to such an extent that of the familiar _cypris_ it is said, "until quite lately males in this genus were unknown; and up to the present time no male has been found in the british islands" (brady and norman, 1896). on the other hand, the ejaculatory duct with its verticillate sac in the male of _cypris_ and other genera is a feature scarcely less remarkable. (b) _bairdiidae_, which have the valves smooth, with the hinge untoothed. (c) _cytheridae_ (? including _paradoxostomatidae_ of brady and norman), in which the valves are usually sculptured, with toothed hinge. of this family the members are almost exclusively marine, but _limnicythere_ is found in fresh water, and _xestoleberis bromeliarum_ (fritz muller) lives in the water that collects among the leaves of bromelias, plants allied to the pine-apples. (d) _darwinulidae_, including the single species _darwinula stevensoni_, brady and robertson, described as "perhaps the most characteristic entomostracan of the east anglian fen district." (e) _cytherellidae_, which, unlike the ostracoda in general, have the hinder part of the body segmented, at least ten segments being distinguishable in the female. they have the valves broad at both ends, and were placed by sars in a separate tribe, called platycopa. the range in time of the ostracoda is so extended that, in g.w. muller's opinion, their separation into the families now living may have already taken place in the cambrian period. their range in space, including carriage by birds, may be coextensive with the distribution of water, but it is not known what height of temperature or how much chemical adulteration of the water they can sustain, how far they can penetrate underground, nor what are the limits of their activity between the floor and the surface of aquatic expanses, fresh or saline. in individual size they have never been important, and of living forms the largest is one of recent discovery, _crossophorus africanus_, a cypridinid about three-fifths of an inch (15.5 mm.) long; but a length of one or two millimetres is more common, and it may descend to the seventy-fifth of an inch. by multitude they have been, and still are, extremely important. though the exterior is more uniform than in most groups of crustacea, the bivalved shell or carapace may be strongly calcified and diversely sculptured (fig. 2), or membranaceous and polished, hairy or smooth, oval or round or bean-shaped, or of some less simple pattern; the valves may fit neatly, or one overlap the other, their hinge may have teeth or be edentulous, and their front part may be excavated for the protrusion of the antennae or have no such "rostral sinus." by various modifications of their valves and appendages the creatures have become adapted for swimming, creeping, burrowing, or climbing, some of them combining two or more of these activities, for which their structure seems at the first glance little adapted. considering the imprisonment of the ostracod body within the valves, it is more surprising that the _asteropidae_ and _cypridinidae_ should have a pair of compound and sometimes large eyes, in addition to the median organ at the base of the "frontal tentacle," than that other members of the group should be limited to that median organ of sight, or have no eyes at all. the median eye when present may have or not have a lens, and its three pigment-cups may be close together or wide apart and the middle one rudimentary. as might be expected, in thickened and highly embossed valves thin spaces occur over the visual organ. the frontal organ varies in form and apparently in function, and is sometimes absent. the first antennae, according to the family, may assist in walking, swimming, burrowing, climbing, grasping, and besides they carry sensory setae, and sometimes they have suckers on their setae (see brady and norman on _cypridina norvegica_). the second antennae are usually the chief motor-organs for swimming, walking and climbing. the mandibles are normally five-jointed, with remnants of an outer branch on the second joint, the biting edge varying from strong development to evanescence, the terminal joints or "palp" giving the organ a leg-like appearance and function, which disappears in suctorial genera such as _paracytherois_. the variable first maxillae are seldom pediform, their function being concerned chiefly with nutrition, sensation and respiration. the variability in form and function of the second maxillae is sufficiently shown by the fact that g.w. muller, our leading authority, adopts the confusing plan of calling them second maxillae in the _cypridinidae_ (including _asteropidae_), maxillipeds in the _halocypridae_ and _cyprididae_, and first legs in the _bairdiidae_, _cytheridae_, _polycopidae_ and _cytherellidae_, so that in his fine monograph he uses the term first leg in two quite different senses. the first legs, meaning thereby the sixth pair of appendages, are generally pediform and locomotive, but sometimes unjointed, acting as a kind of brushes to cleanse the furca, while in the _polycopidae_ they are entirely wanting. the second legs are sometimes wanting, sometimes pediform and locomotive, sometimes strangely metamorphosed into the "vermiform organ," generally long, many-jointed, and distally armed with retroverted spines, its function being that of an extremely mobile cleansing foot, which can insert itself among the eggs in the brood-space, between the branchial leaves of _asterope_ (fig. 3), and even range over the external surface of the valves. the "brush-formed" organs of the podocopa are medially placed, and, in spite of their sometimes forward situation, muller believes among other possibilities that they and the penis in the _cypridinidae_ may be alike remnants of a third pair of legs, not homologous with the penis of other ostracoda (podocopa included). the furca is, as a rule, a powerful motor-organ, and has its laminae edged with strong teeth (ungues) or setae or both. the young, though born with valves, have at first a nauplian body, and pass through various stages to maturity. [illustration: fig. 2.--_cythereis ornata_ (g.w. muller). one eye-space is shown above on the left.] [illustration: fig. 3.--_asterope arthuri_. left valve removed. m, end of adductor muscle. oc, eye. ai, second antenna. mx. 1, first maxilla. mx. 2, second maxilla. p. 1, first foot. v. o, vermiform organ. br, seven branchial leaves. f, projecting ungues of the furca.] brady and norman, in their _monograph of the ostracoda of the north atlantic and north-western europe_ (1889), give a bibliography of 125 titles, and in the second part (1896) they give 55 more. the lists are not meant to be exhaustive, any more than g.w. muller's literature list of 125 titles in 1894. they do not refer to latreille, 1802, with whom the term ostracoda originates. copepoda.--the body is not encased in a bivalved shell; its articulated segments are at most eleven, those behind the genital segment being without trace of limbs, but the last almost always carrying a furca. sexes separate, fertilization by spermatophores. ova in single or double or rarely several packets, attached as ovisacs or egg-strings to the genital openings, or enclosed in a dorsal marsupium, or deposited singly or occasionally in bundles. the youngest larvae are typical nauplii. the next, the copepodid or cyclopid, stage is characterized by a cylindrical segmented body, with fore- and hind-body distinct, and by having at most six cephalic limbs and two pairs of swimming feet. the order thus defined (see giesbrecht and schmeil, _das tierreich_, 1898), with far over a thousand species (hansen, 1900), embraces forms of extreme diversity, although, when species are known in all their phases and both sexes, they constantly tend to prove that there are no sharply dividing lines between the free-living, the semi-parasitic, and those which in adult life are wholly parasitic and then sometimes grotesquely unlike the normal standard. giesbrecht and hansen have shown that the mouth-organs consist of mandibles, first and second maxillae and maxillipeds; and claus himself relinquished his long-maintained hypothesis that the last two pairs were the separated exopods and endopods of a single pair of appendages. thorell's classification (1859) of gnathostoma, poecilostoma, siphonostoma, based on the mouth-organs, was long followed, though almost at the outset shown by claus to depend on the erroneous supposition that the poecilostoma were devoid of mandibles. brady added a new section, choniostomata, in 1894, and another, leptostomata, in 1900, each for a single species. canu in 1892 proposed two groups, monoporodelphya and diporodelphya, the copulatory openings of the female being paired in the latter, unpaired in the former. it may be questioned whether this distinction, however important in itself, would lead to a satisfactory grouping of families. in the same year giesbrecht proposed his division of the order into gymnoplea and podoplea. in appearance an ordinary copepod is divided into fore- and hind-body, of its eleven segments the composite first being the head, the next five constituting the thorax, and the last five the abdomen. the coalescence of segments, though frequent, does not after a little experience materially confuse the counting. but there is this peculiarity, that the middle segment is sometimes continuous with the broader fore-body, sometimes with the narrower hind-body. in the former case the hind-body, consisting only of the abdomen, forms a pleon or tail-part devoid of feet, and the species so constructed are gymnoplea, those of the naked or footless pleon. in the latter case the middle segment almost always carries with it to the hind-body a pair of rudimentary limbs, whence the term podoplea, meaning species that have a pleon with feet. it may be objected that hereby the term pleon is used in two different senses, first applying to the abdomen alone and then to the abdomen plus the last thoracic segment. even this verbal flaw would be obviated if giesbrecht could prove his tentative hypothesis, that the gymnoplea may have lost a pre-genital segment of the abdomen, and the podoplea may have lost the last segment of the thorax. the classification is worked out as follows:-- 1. _gymnoplea._--first segment of hind-body footless, bearing the orifices of the genital organs (in the male unsymmetrically placed); last foot of the fore-body in the male a copulatory organ; neither, or only one, of the first pair of antennae in the male geniculating; cephalic limbs abundantly articulated and provided with many plumose setae; heart generally present. animals usually free-living, pelagic (giesbrecht and schmeil). this group, with 65 genera and four or five hundred species, is divided by giesbrecht into tribes: (a) amphaskandria. in this tribe the males have both antennae of the first pair as sensory organs. there is but one family, the _calanidae_, but this is a very large one, with 26 genera and more than 100 species. among them is the cosmopolitan _calanus finmarchicus_, the earliest described (by bishop gunner in 1770) of all the marine free-swimming copepoda. among them also is the peacock calanid, _calocalanus pavo_ (dana), with its highly ornamented antennae and gorgeous tail, the most beautiful species of the whole order (fig. 4). (b) heterarthrandria. here the males have one or the other of the first pair of antennae modified into a grasping organ for holding the female. there are four families, the _diaptomidae_ with 27 genera, the _pontellidae_ with 10, the _pseudocyclopidae_ and _candaciidae_ each with one genus. the first of these families is often called _centropagidae_, but, as sars has pointed out, _diaptomus_ (westwood, 1836) is the oldest genus in it. of 177 species valid in the family giesbrecht and schmeil assign 67 to _diaptomus_. in regard to one of its species dr brady says: "in one instance, at least (talkin tarn, cumberland) i have seen the net come up from a depth of 6 or 8 ft. below the surface with a dense mass consisting almost entirely of _d. gracilis_." the length of this net-filling species is about a twentieth of an inch. [illustration: fig. 4.--_calocalanus pavo_ (dana).] 2. _podoplea._--the first segment of the hind-body almost always with rudimentary pair of feet; orifices of the genital organs (symmetrically placed in both sexes) in the following segment; neither the last foot of the fore-body nor the rudimentary feet just mentioned acting as a copulatory organ in the male; both or neither of the first pair of antennae in the male geniculating; cephalic limbs less abundantly articulated and with fewer plumose setae or none, but with hooks and clasping setae. heart almost always wanting. free-living (rarely pelagic) or parasitic (giesbrecht and schmeil). this group is also divided by giesbrecht into two tribes, ampharthrandria and isokerandria. in 1892 he distinguished the former as those in which the first antennae of the male have both members modified for holding the female, and the genital openings of the female have a ventral position, sometimes in close proximity, sometimes strongly lateral; the latter as those in which the first antennae of the male are similar to those of the female, the function of holding her being transferred to the male maxillipeds, while the genital openings of the female are dorsal, though at times strongly lateral. in 1899, with a view to the many modifications exhibited by parasitic and semi-parasitic species, the definitions, stripped of a too hampering precision, took a different form: (a) ampharthrandria. "swimming podoplea with geniculating first antennae in the male sex, and descendants of such; first antennae in female and male almost always differently articulated." the families occupy fresh water as well as the sea. naturally "descendants" which have lost the characteristic feature of the definition cannot be recognized without some further assistance than the definition supplies. of the families comprised, the _mormonillidae_ consist only of _mormonilla_ (giesbrecht), and are not mentioned by giesbrecht in 1899 in the grouping of this section. the _thaumatoessidae_ include _thaumatoessa_ (kroyer), established earlier than its synonym _thaumaleus_ (kroyer), or than _monstrilla_ (dana, 1849). the species are imperfectly known. the defect of mouth-organs probably does not apply to the period of youth, which some of them spend parasitically in the body-cavity of worms (giard, 1896). to the _cyclopidae_ six genera are allotted by giesbrecht in 1900. _cyclops_ (o.f. muller, 1776), though greatly restricted since muller's time, still has several scores of species abundantly peopling inland waters of every kind and situation, without one that can be relied on as exclusively marine like the species of _oithona_ (baird). the _misophriidae_ are now limited to _misophria_ (boeck). the presence of a heart in this genus helps to make it a link between the podoplea and gymnoplea, though in various other respects it approaches the next family. the _harpacticidae_ owe their name to the genus _arpacticus_ (milne-edwards, 1840). brady in 1880 assigns to this family 33 genera and 81 species. canu (1892) distinguishes eight sub-families, _longipediinae_, _peltidiinae_, _tachidiinae_, _amymoninae_, _harpacticinae_, _idyinae_, _canthocamptinae_ (for which _canthocampinae_ should be read), and _nannopinae_, adding _stenheliinae_ (brady) without distinctive characters for it. the _ascidicolidae_ have variable characters, showing a gradual adaptation to parasitic life in tunicates. giesbrecht (1900) considers canu quite right in grouping together in this single family those parasites of ascidians, simple and compound, which had been previously distributed among families with the more or less significant names _notodelphyidae_, _doropygidae_, _buproridae_, _schizoproctidae_, _kossmechtridae_, _enterocolidae_, _enteropsidae_. further, he includes in it his own _enterognathus comatulae_, not from an ascidian, but from the intestine of the beautiful starfish _antedon rosaceus_. the _asterocheridae_, which have a good swimming capacity, except in the case of _cancerilla tubulata_ (dalyell), lead a semi-parasitic life on echinoderms, sponges, &c., imbibing their food. giesbrecht, displacing the older name _ascomyzontidae_, assigns to this family 21 genera in five subfamilies, and suggests that the long-known but still puzzling _nicothoe_ from the gills of the lobster might be placed in an additional subfamily, or be made the representative of a closely related family. the _dichelestiidae_, on account of their sometimes many-jointed first antennae, are referred also to this tribe by giesbrecht. (b) isokerandria. "swimming podoplea without genicullating first antennae in the male sex, and descendants of such. first antennae of male and female almost always articulated alike." to this tribe giesbrecht assigns the families _clausidiidae_, _corycaeidae_, _oncaeidae_, _lichomolgidae_, _ergasilidae_, _bomolochidae_, _clausiidae_, _nereicolidae_. here also must for the time be placed the _caligidae_, _philichthyidae_ (_philichthydae_ of vogt, carus, claus), _lernaeidae_, _chondracanthidae_, _sphaeronellidae_ (better known as _choniostomatidae_, from h.j. hansen's remarkable study of the group), _lernaeopodidae_, _herpyllobiidae_, _entomolepidae_. for the distinguishing marks of all these, the number of their genera and species, their habits and transformations and dwellings, the reader must be referred to the writings of specialists. sars (1901) proposed seven suborders--calanoida, harpacticoida, cyclopoida, notodelphoida, monstrilloida, caligoida, lernaeoida. authorities.--(the earlier memoirs of importance are cited in giesbrecht's _monograph of naples_, 1892); canu, "hersiliidae," _bull. sci. france belgique_, ser. 3, vol. i. p. 402 (1888); and _les copepodes du boulonnais_ (1892); cuenot, _rev. biol. nord france_, vol. v. (1892); giesbrecht, "pelag. copepoden." _f. u. fl. des golfes von neapel_ (mon. 19, 1892); hansen, _entomol. med._ vol. iii. pt. 5 (1892); i.c. thompson, "copepoda of liverpool bay," _trans. liv. biol. soc._ vol. vii. (1893); schmeil, "deutschlands copepoden," _bibliotheca zoologica_ (1892-1897); brady, _journ. r. micr. soc._ p. 168 (1894); t. scott, "entomostraca from the gulf of guinea," _trans. linn. soc. london_, vol. vi. pt. 1 (1894); giesbrecht, _mitteil. zool. stat. neapel_, vol. xi. p. 631; vol. xii. p. 217 (1895); t. and a. scott, _trans. linn. soc. london_, ser. 2, vol. vi. p. 419 (1896); hansen "choniostomatidae" (1897); sars, _proc. mus. zool. st petersburg_, "caspian entomostraca" (1897); giesbrecht and schmeil, "copepoda gymnoplea," _das tierreich_ (1898); giesbrecht, "asterocheriden," _f. u. fl. neapel_ (mon. 25, 1899); bassett-smith, "copepoda on fishes," _proc. zool. soc. london_, p. 438 (1899); brady, _trans. zool. soc. london_, vol. xv. pt. 2, p. 31 (1899); sars, _arch. naturv._ vol. xxi. no. 2 (1899); giesbrecht, _mitteil. zool. stat. neapel_, vol. xiv. p. 39 (1900); scott, "fish parasites," _scottish fishery board_, 18th ann. rep. p. 144 (1900); stebbing, _willey's zool. results_, pt. 5, p. 664 (1900); embleton, _journ. linn. soc. london_, vol. xxviii. p. 211 (1901); sars, _crustacea of norway_, vol. iv. (1901). (t. r. r. s.)