Part 43

This species of personal ornament has been exceedingly common in Europe from prehistoric times onward. The bracelets of the Bronze Age were of either gold or bronze, silver being then unknown. In shape they were oval and penannular with expanding or trumpet-shaped ends, having an opening between them of about half an inch to enable them to be easily slipped over the wrist. Those of gold were generally plain, hammered rods, bent to the requisite shape, but those of bronze were often chased with decorative designs. Some forms of spiral armlets of bronze, peculiar to Germany and Scandinavia, covered the whole fore-arm, and were doubtless intended as much for defence against a sword-stroke as for ornament. Among the nations of classical antiquity, bracelets were worn by both sexes of the Etruscans; by women only among the Greeks, except in orientalized communities. Among the Romans they were worn by women only as a rule, but they are also recorded to have been used during the empire by _nouveaux riches_, and by some of the emperors. It should also be mentioned that bracelets were conferred as a military decoration in the field.

[Illustration: From _La Grande Encyclopedie_.

FIG. 2.--Greek Bracelet, Hermitage.]

The bracelets of the Greeks are of two leading types, both of which were also familiar to the Assyrians. The one class were in the form of coiled spirals, usually in the form of snakes, a term which Pollux gives as a synonym for bracelet. The other class were stiff penannular hoops, capable of being slightly opened. In such examples the terminals are finely finished as rams' heads, lions' heads, or (as in the accompanying figure from a bracelet found at Kuloba) as enamelled sphinxes. In late Etruscan art the bracelet may be formed of consecutive panels, as often in modern jewelry.

[Illustration: From La Grande Encydopedie.

FIG. 3.--Etruscan Bracelet, Louvre.]

The spiral forms were common in the Iron Age of northern Europe, while silver bracelets of great elegance, formed of plaited and intertwisted strands of silver wire, and plain penannular hoops, round or lozenge-shaped in section and tapering to the extremities, became common towards the close of the pagan period. The late Celtic period in Britain was characterized by serpent-shaped bracelets and massive armlets, with projecting ornaments of solid bronze and perforations filled with enamel. In the middle ages bracelets were much less commonly used in Europe, but the custom has continued, to prevail among Eastern nations to the present time, and many of the types that were common in Europe in prehistoric times are still worn in central Asia.

A treatise, _De Armillis Veterum_, by Thomas Bartholinus, was published at Amsterdam in 1676.

BRACHIOPODA, an important and well-defined but extremely isolated class of invertebrates. The group may be defined as follows: Sessile solitary _Coelomata_ with bivalved shells usually of unequal size and arranged dorso-ventrally. The head is produced into ciliated arms bearing tentacles. They reproduce sexually, and with doubtful exceptions are of separate sexes.

The name Brachiopod ([Greek: brachion], an arm, and [Greek: pous, podos], a foot) was proposed for the class by F. Cuvier in 1805, and by A.M.C. Dumeril in 1809, and has since been very extensively adopted. The division of the group into _Ecardines_ (_Inarticulata_), with no hinge to the shell and with an alimentary canal open at both ends, and _Testicardines_ (_Articulata_), with a hinge between the dorsal and ventral valves and with no anus, was proposed by Owen and has been adopted by nearly all authors. In a later scheme based on our increased knowledge of fossil forms, the Brachiopoda are divided into four primary groups (orders). This is given at the end of the article, but it must not be forgotten that the existing forms with an anus (Ecardines) differ markedly from the aproctous members of the group (Testicardines).

[Illustration: Figs. 1-11.--Various forms of Brachiopoda.

1. _Magellania [Waldheimia] cranium_. A, ventral, B, dorsal valve.

2. _Rhynchonella (Hemithyris) psittacea_.

3. and 4. _Thecidea_.

5. _Spirifer_. Dorsal valve, showing calcareous spiral coils.

6. _Orthis calligramma_.

7. _Leptaena transversalis_. A, ventral, B, dorsal valve.

8. _Productus horridus_.

9. _Lingula pyramidata_ (after Morse).

10. _Discinisca lamellosa_.

11. _Crania anomala_ Interior of dorsal valve, showing muscular impressions and labial appendages.]

The soft body of the Brachiopod is in all cases protected by a shell composed of two distinct valves; these valves are always, except in cases of malformation, equal-sided, but not equivalved. The valves are, consequently, essentially symmetrical, which is not the case with the Lamellibranchiata,--so much so, that certain Brachiopod shells were named _Lampades_, or lamp shells, by some early naturalists; but while such may bear a kind of resemblance to an antique Etruscan lamp, by far the larger number in no way resemble one. The shell is likewise most beautiful in its endless shapes and variations. In some species it is thin, semi-transparent and glassy, in others massive. Generally the shell is from a quarter of an inch to about 4 in. in size, but in certain species it attains nearly a foot in breadth by something less in length, as is the case with _Productus giganteus_. The valves are also in some species very unequal in their respective thickness, as may be seen in _Productus_ (_Daviesiella_)[1] _llangollensis_, _Davidsonia verneuilii_, &c., and while the space allotted to the animal is very great in many species, as in _Terebratula sphaeroidalis_, it is very small in others belonging to _Strophomena_, _Leptaena_, _Chonetes_, &c. The ventral valve is usually the thickest, and in some forms is six or seven times as great as the opposite one. The outer surface of many of the species presents likewise the most exquisite sculpture, heightened by brilliant shades, or spots of green, red, yellow and bluish black. Traces of the original colour have also been preserved in some of the fossil forms; radiating bands of a reddish tint have been often seen in well-preserved examples of _Terebratula_ (_Dielasma_) _hastata_, _T_. (_Dielasma_) _sacculus_, _T. communis_, _T. biplicata_, and of several others. Some specimens of _T. carnea_ are of a beautiful pale pink colour when first removed from their matrix, and E. Deslongchamps has described the tint of several Jurassic species.

The valves are distinguished as _dorsal_ and _ventral_. The ventral valve is usually the larger, and in many genera, such as _Terebratula_ and _Rhynchonella_, has a prominent beak or umbo, with a circular or otherwise shaped foramen at or near its extremity, partly bounded by one or two plates, termed a deltidium. Through the foramen passes a peduncle, by which the animal is in many species attached to submarine objects during at least a portion of its existence. Other forms show no indication of ever having been attached, while some that had been moored by means of a peduncle during the early portion of their existence have become detached at a more advanced stage of life, the opening becoming gradually cicatrized, as is so often seen in _Leptaena rhomboidalis_, _Orthisina anomala_, &c. Lastly, some species adhere to submarine objects by a larger or smaller portion of their ventral valve, as is the case with many forms of _Crania_, _Thecidium_, _Davidsonia_, &c. Some _Cranias_ are always attached by the whole surface of their lower or ventral valve, which models itself and fills up all the projections or depressions existing on either the rock, shell or coral to which it adhered. These irregularities are likewise, at times, reproduced on the upper or dorsal valve. Some species of _Strophalosia_ and _Productus_ seem also to have been moored during life to the sandy or muddy bottoms on which they lived, by the means of tubular spines often of considerable length. The interior of the shell varies very much according to families and genera. On the inner surface of both valves several well-defined muscular, vascular and ovarian impressions are observable; they form either indentations of greater or less size and depth, or occur as variously shaped projections. In the _Trimerellidae_, for example, some of the muscles are attached to a massive or vaulted platform situated in the medio-longitudinal region of the posterior half or umbonal portion of both valves. In addition to these, there exists in the interior of the _dorsal_ valve of some genera a variously modified, thin, calcified, ribbon-shaped skeleton for the support of the ciliated arms, and the form of this ribbon serves as one of the chief generic characters of both recent and extinct forms. This brachial skeleton is more developed in some genera than in others. In certain forms, as in _Terebratula_ and _Terebratulina_, it is short and simple, and attached to a small divided hinge-plate, the two riband-shaped lamina being bent upwards in the middle (fig. 15). The cardinal process is prominent, and on each side of the hinge-plate are situated the dental sockets; the loop in _Terebratulina_ becomes annular in the adult by the union of its crural processes (fig. 16). In _Magellania_ [_Waldheimia_] it is elongated and reflected; the hinge-plate large, with four depressions, under which originates a median septum, which extends more or less into the interior of the shell (figs. 13 and 14). In _Terebratella_ the loop is attached to the hinge-plate and to the septum (fig. 17). In _Megerlia_ it is three times attached, first to the hinge-plate, and then to the septum by processes from the diverging and reflected positions of the loop. In _Magas_ the brachial skeleton is composed of an elevated longitudinal septum reaching from one valve to the other, to which are affixed two pairs of calcareous lamellae, the lower ones riband-shaped; attached first to the hinge-plate, they afterwards proceed by a gentle curve near to the anterior portion of the septum, to the sides of which they are affixed; the second pair originate on both sides of the upper edge of the septum, extending in the form of two triangular anchor-shaped lamellae (fig. 18). In _Bouchardia_ the septum only is furnished with two short anchor-shaped lamellae. Many more modifications are observable in different groups of which the great family _Terebratulidae_ is composed. In _Thecidium_ (figs. 3,4) the interior of the dorsal valve is variously furrowed to receive the lophophore folded in two or more lobes. In the family _Spiriferidae_ there are two conical spires directed outwards, and nearly filling the cavity of the shell (fig. 5); while in _Atrypa_ the broad spirally coiled lamellae are vertical, and directed toward the centre of the dorsal valve. In the _Rhynchonellidae_ there are two short slender curved laminae, while in many genera and even families, such as the _Productidae, Strophomenidae, Lingulidae, Discinidae_, &c., there exists no calcified support for the labial appendages. The ventral valve in many of the genera is provided with two curved hinge-teeth, which fit into corresponding sockets in the opposite valve, so that the valves cannot be separated without breaking one of the teeth.

[Illustration: FIGS. 12-18.

12. _Magellania [Waldheimia] flavescens_. Interior of ventral valve. f, foramen; d, deltidium; t, teeth; a, adductor impressions (= occlusors, _Hancock_); c, divaricator (= cardinal muscles, _King_, = muscles diducteurs principaux, _Gratiolet_); c', accessory divaricators (muscles diducteurs accessoires, _Gratiolet_); b, ventral adjuster (= ventral peduncular muscles, or muscles du pedoncule paire superieure, _Gratiolet_); b', peduncular muscle.

13. _Magellania [Waldheimia] flavescens_. Interior of dorsal valve. c, c', cardinal process; b', b', hinge-plate; s, dental sockets; l, loop; q, crura; a, a', adductor impressions; c, accessory divaricator; b, peduncle muscles; ss, septum.

14. _Magellania [Waldheimia] flavescens_. Longitudinal section of valves. A, ventral, B, dorsal valves; l, loop; q, crura; ss, septum; c, cardinal process.

15. _Terebratula (Liothyris) vitrea_. Interior of dorsal valve. l, loop; b, hinge-plate; c, cardinal process.

16. Loop of _Terebratulina caput serpentis_.

17. Longitudinal section of _Terebratella dorsata_. (References as in fig. 14.)

18. Longitudinal section of _Magas pumilus_.]

[Illustration: FIG. 19.--_Magellania [Waldheimia] flavescens_. Interior of dorsal valve, to show the position of the labial appendages. v, Mouth. (A portion of the fringe of cirri is removed to show the brachial membrane and a portion of the spiral extremities of the arms.)]

Each valve of the shell is lined by a mantle which contains prolongations of the body cavity. The outer surfaces of the mantle secrete the shell, which is of the nature of a cuticle impregnated by calcareous salts. These often have the form of prisms of calcite surrounded by a cuticular mesh work; the whole is nourished and kept alive by processes, which in _Crania_ are branched; these perforate the shell and permit the access of the coelomic fluid throughout its substance. These canals are closed externally and are absent in _Rhynchonella_, where the amount of calcareous deposit is small. In _Lingula_ the shell is composed of alternate layers of chitin and of phosphate of lime. The free edges of the mantle often bear chitinous bristles or setae which project beyond the shell. As in the case of the Lamellibranchiata, the shell of the adult is not a direct derivative of the youngest shell of the larva. The young Brachiopod in all its species is protected by an embryonic shell called the "protegulum," which sometimes persists in the umbones of the adult shells but is more usually worn off. In all species it has the same shape, a shape which has been retained in the adult by the Lower Cambrian genus _Iphidea_.

[Illustration: FIG. 20.--_Magellania [Waldheimia] flavescens_. Logitudinal section with a portion of the animal.

d, h, Brachial appendages. a, Adductor c, c', Divaricator muscles. s, Septum. v, Mouth. z, Exremity of alimentary tube. The penduncular muscules have been purposely omitted.]

The body of the Brachiopod usually occupies about the posterior half of the space within the shell. The anterior half of this space is lined by the inner wall of the mantle and is called the mantle cavity. This cavity lodges the arms, which are curved and coiled in different ways in different genera. The water which bears the oxygen for respiration and the minute organisms upon which the Brachiopod feeds is swept into the mantle cavity by the action of the cilia which cover the arms, and the eggs and excreta pass out into the same cavity. The mouth lies in the centre of the anterior wall of the body. Its two lips fusing together at the corners of the mouth are prolonged into the so-called arms. These arms, which together form the lophophore, may be, as in _Cistella_, applied flat to the inner surface of the dorsal mantle fold, but more usually they are raised free from the body like a pair of moustaches, and as they are usually far too long to lie straight in the mantle cavity, they are folded or coiled up. The brachial skeleton which in many cases supports the arms has been mentioned above.

[Illustration: FIG. 21.--A diagram of the left half of an _Argiope_ (_Megathyris_), which has been bisected in the median plane.

1. The ventral valve. 2. The dorsal valve. 3. The pedicle. 4. The mouth. 5. Lip which overhangs the mouth and runs all round the lophophore. 6. Tentacles. 7. Ovary in dorsal valve. 8. Liver diverticula. 9. Occlusor muscle--its double origin is shown. 10. Internal opening of left nephridium. 11. External opening of the same. 12. Ventral adjustor. 13. Divaricator muscle. 14. Sub-oesophageal nerve ganglion. 15. The heart. 16. Dorsal adjustor muscle.]

A transverse section through the arm (fig. 22) shows that it consists of a stout base, composed of a very hyaline connective tissue not uncommon in the tissues of the Brachiopoda, which is traversed by certain canals whose nature is considered below under the section (_The Body Cavity_) devoted to the coelom. Anteriorly this base supports a gurrie or gutter, the pre-oral rim of which is formed by a simple lip, but the post-oral rim is composed of a closely set row of tentacles. These may number some thousands, and they are usually bent over and tend to form a closed cylinder of the gutter. Each of these tentacles (fig. 22) is hollow, and it contains a diverticulum from the coelom, a branch of the vascular system, a nerve and some muscle-fibres. Externally on two sides and on the inner surface the tentacles are ciliated, and the cilia are continued across the gutter to the lip and even on the outer surface of the latter. These cilia pass on any diatoms and other minute organism which come within their range of action to the capacious oval mouth, which appears as a mere deepening of the gutter in the middle line. In _Terebratulina, Rhynchonella, Lingula_, and possibly other genera, the arms can be unrolled and protruded from the opened shell; in this case the tentacles also straighten themselves and wave about in the water.

_The Body Cavity._--The various internal organs of the brachiopod body, the alimentary canal and liver, the excretory organs, the heart, numerous muscles and the reproductive organs, are enclosed in a cavity called the body cavity, and since this cavity (i.) is derived from the archicoel and is from the first surrounded by meroblast, (ii.) communicates with the exterior through the nephridia or excretory organs, and (iii.) gives rise by the proliferation of the cells which line it to the ova and spermatoza, it is of the nature of a true coelom. The coelom then is a spacious chamber surrounding the alimentary canal, and is continued dorsally and ventrally into the sinuses of the mantle (fig. 21). Some of the endothelial cells lining the coelom are ciliated, the cilia keeping the corpusculated fluid contents in movement. Others of the endothelial cells show a great tendency to form muscle fibres. Besides this main coelomic cavity there are certain other spaces which F. Blochmann regards as coelomic, but it must be remembered that his interpretation rests largely on histological grounds, and at present embryological confirmation is wanting. These spaces are as follows:--(i.) the great arm-sinus; (ii.) the small arm-sinus together with the central sinus and the peri-oesophageal sinus, and in _Discinisca_ and _Lingula_, and, to a less extent, in _Crania_, the lip-sinus; (iii.) certain portions of the general body cavity which in _Crania_ are separated off and contain muscles, &c.; (iv.) the cavity of the stalk when such exists. The great arm-sinus of each side of the lophophore lies beneath the fold or lip which together with the tentacles forms the ciliated groove in which the mouth opens. These sinuses are completely shut off from all other cavities, they do not open into the main coelomic space nor into the small arm-sinus, nor does the right sinus communicate with the left. The small arm-sinus runs along the arms of the lophophore at the base of the tentacles, and gives off a blind diverticulum into each of these. This diverticulum contains the blood-vessel and muscle-fibres (fig. 22). In the region of the mouth where the two halves of the small arm-sinus approach one another they open into a central sinus lying beneath the oesophagus and partly walled in by the two halves of the ventral mesentery. This sinus is continued round the oesophagus as the peri-oesophageal sinus, and thus the whole complex of the small arm-sinus has the relations of the so-called vascular system of a Sipunculid. In _Crania_ it is completely shut off from the main coelom, but in _Lingula_ it communicates freely with this cavity. In _Discinisca_ and _Lingula_ there is further a lip-sinus or hollow system of channels which traverses the supporting tissue of the edge of the mantle and contains muscle-fibres. It opens into the peri-oesophageal sinus. It is better developed and more spacious in _Lingula_ than in _Discinisca._ In _Crania_, where only indications of the lip-sinus occur, there are two other closed spaces. The posterior occlusor muscles lie in a special closed space which Blochmann also regards as coelomic. The posterior end of the intestine is similarly surrounded by a closed coelomic space known as the peri-anal sinus in which the rectum lies freely, unsupported by mesenteries. All these spaces contain a similar coagulable fluid with sparse corpuscles, and all are lined by ciliated cells. There is further a great tendency for the endothelial cells to form muscles, and this is especially pronounced in the small arm-sinus, where a conspicuous muscle is built up. The mantle-sinuses which form the chief spaces in the mantle are diverticula of the main coelomic cavity. In _Discinisca_ they are provided with a muscular valve placed at their point of origin. They contain the same fluid as the general coelom. The stalk is an extension of the ventral body-wall, and contains a portion of the coelom which, in _Discinisca_ and _Lingula_, remains in communication with the general body cavity.

[Illustration: FIG. 22.--Diagrammatic section through an arm of the lophophore of _Crania_. Magnified; after Blochmann.

1. The lip. 2. The base of a tentacle bisected in the middle line. 3. Great arm-sinus. 4. Small arm-sinus, containing muscle-fibres. 5. Tentacular canal. 6. External tentacular muscle. 7. Tentacular blood-vessel arising from the cut arm-vessel in the small arm-sinus. 8. Chief arm-nerve. 9. Secondary arm-nerve. 10. Under arm-nerve.]

_The Alimentary Canal_.--The mouth, which is quite devoid of armature, leads imperceptibly into a short and dorsally directed oesophagus. The latter enlarges into a spherical stomach into which open the broad ducts of the so-called liver. The stomach then passes into an intestine, which in the Testicardines (Articulata) is short, finger-shaped and closed, and in the Ecardines (Inarticulata) is longer, turned back upon its first course, and ends in an anus. In _Lingula_ and _Discina_ the anus lies to the right in the mantle-cavity, but in _Crania_ it opens medianly into a posterior extension of the same. Apart from the asymmetry of the intestine caused by the lateral position of the anus in the two genera just named, Brachiopods are bilaterally symmetrical animals.

The liver consists of a right and left half, each opening by a broad duct into the stomach. Each half consists of many lobes which may branch, and the whole takes up a considerable proportion of the space in the body cavity. The food passes into these lobes, which may be found crowded with diatoms, and without doubt a large part of the digestion is carried on inside the liver. The stomach, oesophagus and intestine are ciliated on their inner surface. The intestine is slung by a median dorsal and ventral mesentery which divides the body cavity into two symmetrically shaped halves; it is "stayed" by two transverse septa, the anterior or gastroparietal band running from the stomach to the body wall and the posterior or ileoparietal band running from the intestine to the body wall. None of these septa is complete, and the various parts of the central body cavity freely communicate with one another. In _Rhynchonella_, where there are two pairs of kidneys, the internal opening of the anterior pair is supported by the gastroparietal band and that of the posterior pair by the ileoparietal band. The latter pair alone persists in all other genera.

The kidneys or nephridia open internally by wide funnel-shaped nephridiostomes and externally by small pores on each side of the mouth near the base of the arms. Each is short, gently curved and devoid of convolutions. They are lined by cells charged with a yellow or brown pigment, and besides their excretory functions they act as ducts through which the reproductive cells leave the body.

_Circulatory System._--The structures formerly regarded as pseudohearts have been shown by Huxley to be nephridia; the true heart was described and figured by A. Hancock, but has in many cases escaped the observation of later zoologists. F. Blochmann in 1884, however, observed this organ in the living animal in species of the following genera:--_Terebratulina, Magellania_ [_Waldheimia_]_, Rhynchonella, Megathyris_ (_Argiope_), _Lingula_, and _Crania_ (fig. 21). It consists of a definite contractile sac or sacs lying on the dorsal side of the alimentary canal near the oesophagus, and in preparations of _Terebratulina_ made by quickly removing the viscera and examining them in sea-water under a microscope, he was able to count the pulsations, which followed one another at intervals of 30-40 seconds.