|

the points A and B as centres, and the radii A B and B A
respectively, describe the semicircles A C D, B C E, intersecting
each other in the point c. Bisect A B in F, and through the
point c draw F G perpendicular to A B or X Y. Next trisect the
arc A C in the points H and K, and the arc B C in the points
L and M; and from the point A, through the points M, L, and c
in the arc B C, draw the straight lines A N, A O, A P of indefinite
length; and from B, through the points H, K, and c, in the arc
A.C, draw the straight lines B S, B R, and B Q, also of indefinite
length. From the points A and B draw the straight lines A T,
BU to the points, T, U, in which the straight lines B S, A N
cut the semicircles B CE, A C D; bisect A T, BU in the points
V and w respectively, and through the points v and w draw
the perpendicular lines v I, w z of indefinite length, intersecting
each other and the straight line F G in the point a.
point is the centre of a circle circumscribing the required nona-
gon. From the point a as centre, with the distance a A or a B,
describe the circle Ad B. This circle passes through the extremi-
ties of the given straight line A B, the points T and U in which
the straight lines B S, A N respectively intersect the semicircles
BCE, AC D, and the points c and e in which the straight lines
BQ, W Z and A P, V I intersect each other: it also cuts the
straight lines B R, F G, and A o in the points b, d, and f. Join
Tb, bc, cd, de, ef, and ƒ u: the figure A Tbcdefu B is a
nonagon, and it is described, as required, upon the given straight
line A B.

This

determine them, with an opening of the compasses equal to A B, set off from A, along the arc A G, the arcs A N, N 0, 0 P, and along the arc в H, from B, set off the arcs B Q, Q R, R S. Join the chords A N, NO, O P, PG, BQ, Q R, RS, S H. The figure AB QR SHFG PON is an undecagon, and it is described on the given straight line A B, as required.

The construction of the uneven-sided polygons, the heptagon and nonagon, by the aid of the ruler and compasses, have been given to show the learner that there is no regular polygon of any number of sides that could not be constructed without having The reader will have noticed, doubtless, that the method of recourse to the measurement of the angle of the polygon or the constructing an undecagon on a given straight line by a purely angle at the centre of the circumscribing circle. The construction geometrical process, as given above, is similar in all essential of the decagon and dodecagon on any given line by the ruler and details to the process used for constructing a heptagon on a compasses alone we do not give, because either figure may be con- given straight line, and it is based in both cases on the structed by learners, if they will exercise a little thought, and it numerical relation of the straight line on which either is to be will afford them two constructed, to the sides of an isosceles triangle whose vertex is useful exercises to the apex of the polygon, and whose base is the given straight do so. We shall line. In the case of the heptagon, the proportion of the base to therefore conclude the sides of the isosceles, whose vertex is the apex of the polygon, our problems on the is as 1 to 21 or 2-25; and to construct a heptagon on any given construction of the straight line, we have only to produce it indefinitely both ways, regular polygons and find points on either side of each extremity at a distance with the method of equal to 14 of the given line, or to bisect the given line and set constructing an un-off on either side of the perpendicular section straight lines decagon or eleven- equal to 13 of the given line. In the case of the undecagon, sided figure on a the proportion of the base to the side of the isosceles triangle, given straight line, whose apex is the vertex of the polygon, is as 1 to 3 or 3.5; and and then bring our to construct an undecagon on any given straight line, we have Lessons on Geome- only to produce the given straight line indefinitely both ways, try to an end with and set off from either extremity lines equal to 2 of the given a brief description straight line, or to bisect the given line, and from the point of Yof the methods used bisection to set off on either side of it, along the given line profor drawing the el- duced indefinitely, lines equal to 3 times the given straight line. lipse, parabola, and We have added these remarks on the geometrical constructions hyperbola, curves made by the section of a right cone in parti- that we have given of the heptagon and undecagon, in the hope cular directions; the mode of tracing a spiral; and one or two that they may give the student a clue to other geometrical conother things, such as the connection of two curves by a straight structions of a similar character. We also recommend to his line, etc., which may be of practical use to our students. notice the geometrical construction of the nonagon, based on the preliminary construction of an equilateral triangle on the given straight line on which it is required to construct the nonagon, and the trisection of the angles on either side of the base, or the arcs that are described opposite to them by drawing semicircles from either extremity of the base as centres, with a radius equal to the base.

Fig. 80.

N

PROBLEM LVII.-To construct an undecagon on any given straight line.

Let A B (Fig. 81) be the given straight line on which it is required to construct an undecagon. First bisect A B in c, and produce A B indefinitely both ways to x and y. Then along cx set off a line, C D, equal to three times A B, or six times CA, and along c Y set off a line, c E, equal to C D. From the point A as centre, with the distance A E, describe the arc E T, and from the point B as centre, with the distance B D, describe the arc D Z, and let the arcs E T, D Z intersect each other in the point F. This point is the apex of the undecagon, the straight line A B on which it is constructed being considered as its base. From the point F as centre, with a radius equal to A B, draw small arcs cutting the larger arcs D Z, E T in G and H, and draw the chords FG, FH. Join CF: the straight line drawn from c, through F, is perpendicular to A B, and the centre of the circle circumscribing the required undecagon will be in C F. To find the centre, bisect FG, F H in the points K and L, and join A L, B K. The straight lines A L, B K intersect each other and the straight line C F in the point м, which is the centre of the circumscribing circle. From

In drawing figures to exhibit the methods of constructing the different polygons, from the pentagon to the undecagon, that have been given in detail in this and preceding lessons, the student is advised, for the sake of accuracy, to make them on a large scale; as, if he attempt to construct his figures in the limited space in which are drawn the figures that are used to illustrate our Lessons in Geometry, he may fail to complete them to his satisfaction, in consequence of not being able to draw the straight lines and arcs, of which the figures are composed, of suitable fineness, and to subdivide the arcs, whenever it is necessary to do so, with sufficient accuracy. In all cases, for the sake of good practice, the straight line on which a polygon is to be constructed, should never be taken less than an in length.

READING AND ELOCUTION.-XX.

PROMISCUOUS EXERCISES (continued).

II. THE PURITANS,

[Marked for Inflections.]

life with unvaried liberality; and, perhaps, his character may receive some illustration, if he be compared with his master.

Integrity of understanding, and nicety of discernment, were not allotted in a less proportion to Dry'den than to Pope. The rectitude of Dryden's mind was sufficiently shown by the dismission of his poetical préjudices, and the rejection of unnatural thoughts and rugged numbers. But Dryden never desired to apply all the judgment that he had. He wrote, and professed to write, merely for the people; and when he pleased others, he contented himself. He spent no time in struggles to rouse latent powers; he never attempted to make that better which was already good, nor often to mend what he must have known to be faulty. He wrote, as he tells us, with very little consideration: when occasion or necessity called upon him, he poured out what the present moment happened to supply, and, when once it had passed the préss, ejected it from his mind; for when he had no pecuniary interest, he had no further solicitude.

THE Puritans were men whose minds had derived a peculiar character from the daily contemplation of superior beings and eternal interests. Not content with acknowledging, in general terms, an overruling Próvidence, they habitually ascribed évery event to the will of the Great Being, for whose power nothing was too vást, for whose inspéction nothing was too minute. To know Him, to serve Him, to enjoy Him, was with them the great end of existence. They rejected with contempt the ceremonious homage which other sects substituted for the pure worship of the soul. Instead of catching occasional glimpses of the Deity through an obscùring véil, they aspired to gaze fùll on the intolerable brightness, and to commune with Him face to face. Hence originated their contempt for terréstrial distinctions. The difference between the greatest and méanest of mankind seemed to vanish, when compared with the boundless interval which separated the whole race from Him on whom their own eyes were constantly fixed. They recognised no title to superiority but His favour; and, confident of that favour, they despised all the accomplishments and all the dignities of the world. If they were unacquainted with the works of philosophers and poets, they were deeply réad in the óracles of God.supposed to have been written with such regard to the times as might If their names were not found in the registers of heralds, they felt assured that they were recorded in the Book of Life. If their steps were not accompanied by a splendid train of ménials, legions of ministering àngels had charge over them. Their palaces were houses not made with hands; their díadems, crowns of glory which should never fade away!

On the rich and the eloquent, on nòbles and priests, they looked down with contempt; for they esteemed themselves rich in a more précious treasure, and eloquent in a more sublime language; nobles by the right of an earlier creation, and priests by the imposition of a mightier hand. The very meanest of them was a being to whose fate a mysterious and térrible importance belonged,-on whose slightest action the spirits of light and darkness looked with anxious interest; who had been destined, before heaven and earth were created, to enjoy a felicity which should continue, when heaven and earth should have passed away.

Events which shortsighted politicians ascribed to earthly causes, had been ordained on his account. For his sake, èmpires had risen, and flourished, and decayed. For his sake, the Almighty had proclaimed his will by the pèn of the evangelist and the harp of the pròphet. He had been rescued by nó common deliverer, from the grasp of no cómmon foe. He had been ransomed by the sweat of nó vulgar ágony, by the blood of nò éarthly sacrifice. It was for him that the sun had been darkened, that the rocks had been rènt, that the dead had arisen, that all nature had shuddered at the sufferings of her expiring God.

Thus the Puritan was made up of two different mèn, the one all self-abasement, penitence, gratitude, pássion; the other proud, càlm, infléxible, sagàcious. He próstrated himself in the dust before his Maker; but he set his foot on the neck of the king. In his devotional retirement, he prayed with convulsions, and groans, and tears. He was half-maddened by glorious or térrible illusions. He heard the ly`res of angels, or the tempting whispers of fiends. He caught a gleam of the beatific vision, or woke screaming from dreams of everlasting fire. Like Váne, he thought himself entrusted with the scèptre of the millennial year. Like Fleetwood, he cried in the bitterness of his soul, that God had hid his face from him. But when he took his séat in the council, or girt on his sword for wàr, these tempestuous workings of the soul had left nò percéptible trace behind them. People who saw nothing of the godly but their uncouth visages, and heard nothing from them but their groans and their hy'mus, might laugh at them. But those had little reason to laugh, who encountered them in the hall of debate, or in the field of battle.

The Puritans brought to civil and military affairs a coolness of judgment, and an immutability of púrpose, which some writers have thought inconsistent with their religious zeal, but which were in fact the nécessary effects of it. The intensity of their feelings on óne subject made them trànquil on évery other. One overpowering sentiment had subjected to itself pity and hatred, ambition and fear. Death had lost its térrors, and pleasure its charms. They had their smiles and their tears, their ráptures and their sorrows, but not for the things of this world. Enthusiasm had made them stoics, had cleared their minds from every vulgar passion and préjudice, and raised them above the influence of dánger and of corruption.-Macaulay.

III. POPE AND DRYDEN.

[This piece is marked in application of the rules of Inflection.]
Pono professed to have learnt his poetry from Dry'den, whom,
ver an opportunity was presented, he praised through his whole

on emphatic series causes, thus, a succession of falling
second one in each clause falls lower than the first.

Pope was not content to satisfy; he desired to excèl, and therefore always endeavoured to do his best; he did not court the candour, but dared the judgment of his reader, and, expecting no indulgence from others, he showed none to himself. He examined lines and words with minute and punctilious observation, and retouched every part with indefatigable diligence, till he had left nothing to be forgiven. For this reason he kept his pieces very long in his hands, while he considered and rèconsidered them. The only poems which can be hasten their publication, were the two satires of Thirty-eight: of which Dodsley told me, that they were brought to him by the author, that they might be fairly copied. "Every line," said he, 66 was then written twice over; I gave him a clean trànscript, which he sent some time afterwards to me for the préss, with every line written twice over a second time."

His declaration, that his care for his works ceased at their publi cátion, was not strictly true. His parental attention never abandoned them; what he found amiss in the first edition, he silently corrected in those that followed. He appears to have revised the Iliad, and freed it from some of its imperfections; and the Essay on Criticism received many improvements, after its first appearance. It will seldom be found that he altered without adding clearness, élegance, or vigour. Pope had, perhaps, the judgment of Dry'den; but Dryden certainly wanted the diligence of Pope.

In acquired knowledge, the superiority must be allowed to Dry den, whose education was more scholastic, and who, before he became an author, had been allowed more time for study, with better means of information. His mind has a larger range, and he collects his images and illustrations from a more extensive circumference of science. Dryden knew more of man in his general náture, and Pope in his local manners. The notions of Dryden were formed by comprehensive speculation, and those of Pope by minute attention. There is more diguity in the knowledge of Dry'den, and more cértainty in that of Pope.

Poetry was not the sole praise of either: for both excelled likewise in prose: but Pope did not borrow his prose from his predecessor. The style of Dryden is capricious and varied; that of Pope is cautions and uniform. Dryden obeys the motions of his own mind; Pope constrains his mind to his own rules of composition. Dryden is sometimes vehement and rápid; Pope is always smooth, uniform, and gentle. Dryden's page is a natural field, rising into inequalities, and diversified by the varied exuberance of abundant vegetation; Pope's is a velvet lawn, shaven by the scy'the and levelled by the roller.

Of génius, that power which constitutes a poet; that quality without which judgment is cold, and knowledge is inért; that energy which collects, combines, àmplifies, and ánimates; the superiority must, with some hesitation, be allowed to Dry'den. It is not to be inferred, that of this poetical vigour Pope had only a little, because Dryden had more; for every other writer since Milton must give place to Pope; and even of Dry'den it must be said, that if he has brighter paragraphs, he has not better poems. Dryden's performances were always hasty, either excited by some external occasion, or extorted by domestic necessity; he composed without consideration, and published without correction. What his mind could supply at call, or gather in one excursion, was all that he sought, and all that he gave. The dilatory caution of Pope enabled him to condénse his sentiments, to múltiply his images, and to accumulate all that study might produce, or chance might supply'. If the flights of Dryden, therefore, are higher, Pope continues longer on the wing. If of Dryden's fire the blaze is brighter, of Pope's the heat is more régular and constant. Dry'den often surpasses expectation, and Pope never falls below it. Dry den is read with frequent astonishment, and Pope with perpétual delight.-Johnson.

IV. UNIVERSAL DECAY.

[Marked for Rhetorical Pauses, Emphasis, and Inflections.]* We receive such repeated intimations of decay in the world through

The learner having been conducted through the application of the rules for Pauses, Emphasis, and Inflections separately, will now be prepared to study and apply them in conjunction,

1

which we are passing ;- decline | and change and loss, follow decline | and change and loss in such rapid succession, that we can almost catch the sound of universal wasting, and hear the work of desolation going on busily around us. "The mountain | falling cometh to nought, and the rock | is removed out of his place. The waters | wear the stones, the things which grow out of the dust of the earth || are washed

1

eway, and the hope of man is destroyed." Conscious of our own instability, we look about for something to rest on; but we look in vain. The heavens and the earth | had a beginning, and they will have an end. The face of the world is changing, daily and hourly. All animated things grow old and die. The rocks crumble, the trees | fall, the leaves | fade, and the grass | withers. The clouds are flying, and the waters are flowing away from us.

The

The firmest works of min, too, are gradually giving wày: the ivy | clings to the mouldering tower, the brier | hangs ont from the shattered window, and the wall-flower | springs from the disjointed stones. founders of these perishable works || have shared the same fate long ago. If we look back to the days of our ancestors, to the men as well as the dicllings of former times, they become immediately associated in our imaginations, and only make the feeling of instability stronger and deeper than before. In the spacious domes, which once held our fathers, the serpent hisses, and the wild bird | screams. The halls, which once were crowded with all that taste and science | and labour | could procure, which resounded with melody, and were lighted up with beauty, are buried by their own rùins, mocked by their own desòlation. The voice of merriment, and of wailing, the steps of the busy and the idle have ceased in the deserted courts, and the weeds choke the entrances, and the long grass waves upon the hearth-stone. The works of art, the forming hand, the tombs, the very ashes they contained, are all gone.

With regard to the English association not much is to be said, because, while the human urchin is actively mischievous, and often made to smart for it, passively, the other urchins are very harmless except in passive self-defence. The other resemblance, though misleading anatomically, is very marked, on account of the dense covering of sharp spines sticking out in all directions, matted and crossing one another like the spines of the thistle leaf; and also on account of the globular form, which, though temporary in the land urchin, is permanent in the echinus.

The shell of a typical echinus, upon which the spines are set, is a round box of very complex and beautiful structure. It consists of plates of carbonate of lime so closely and accurately fitted together, that, even after the spines have been stripped off, it requires minute examination to discover the lines of division between them. The box has the form of a more or less depressed sphere, varying from the shape of a true globe to that of a Turkish turban. At the two poles of the box are two holes : that which opens on the under side of the animal is the mouth, while that which is found at the centre of the top side is th other end of the food canal. A further examination reveals that the shell is made up of five similar radial divisions, which stretch from pole to pole, and may be thus described :-The central zigzag line, running from mouth to anus, has on either side of it a row of small plates alternating with one another; and on the outer side of each of these rows of plates is a row of small While we thus walk among the ruins of the pást, a sad feeling of holes. There are six of these holes in each plate. Externally insecurity comes over us; and that feeling is by no means diminished to these perforated plates are situated two other rows of larger when we arrive at home. If we turn to our friends, we can hardly plates, one on each side, and these are united at their external speak to them before they bid us farewell. We see them for a few edges to the next radial division of the box by a zigzag line. moments, and in a few moments more their countenances are changed, The outer side of both the perforated plates and the plates and they are sent away. It matters not how near and dear they are. without holes are covered with bosses, each of which has a more The ties which bind us together || are never too close to be parted, or too strong to be broken. Tears were never known to move the king of prominent rounded knob projecting from the top of it, which terrors; neither is it enough that we are compelled to surrender óne, knob has a pit in its centre. 1 These knobs bear the spines. or two, or many of those we love; for though the price is so great, we buy no favour with it, and our hold on those who remain | is as slight as ever. The shadows || all | elude our grasp, and follow one another down the valley. We gain no confidence, then, no feeling of security, by turning to our contémporaries and kindred. We know that the forms which are breathing around us, are as shortlived and fleeting those were, which have been dúst for centuries. The sensation of city, uncertainty, and rúin, is equally strong, whether we muse on what has long been pròstrate, or gaze on what is falling nów, or will fall ' so soon.

If everything which comes under our notice has endured for so short a time, and in so short a time | will be no more, we cannot say | that we receive the least assurance || by thinking on ourselves. When a few more friends | have left, a few more hopes | deceived, and a few more changes | mocked us, "we shall be brought to the grave, and shall remain in the tomb: the clods of the valley shall be sweet unto us, and every man shall follow us, as there are innumerable' befòre us." All

power will have forsaken the strongest, and the loftiest will be laid low,

and every eye I will be closed, and every voice húshed, and every heart will have ceased its beating. And when we have gone ourselves, even our memories will not stay behind us long. A few of the near and dear || will bear our likeness in their bosoms, till they too have arrived at the end of their journey, and entered the dark dwelling of unconsciousness. In the thoughts of others we shall live only till the last sound of the bell, which informs them of our departure, has ceased to vibrate in their ears. A stone, perhaps, may tell some wanderer where we lie, whèn

we came here, and when we went away; but even that will soon refuse to bear us rècord; "time's effacing fingers" I will be busy on its surface, and at length will wear it smooth; and then the stone itself will sink, or crumble, and the wanderer of another age will pass, without a single call upon his sympathy, over our unheeded gràves.-Greenwood.

COMPARATIVE ANATOMY.-VI. ECHINODERMATA (HEDGEHOG-SKINNED ANIMALS.) FROM the earliest times, before Aristotle wrote of animals, the great similarity in outward appearance between the hedgehog, when rolled up in self-defence, and the sea-egg, or echinus, has been so recognised as to cause them to be called by the same In Greek, echinus (exivos) means both the one and the other. In English, we have expanded this superficial association to include the young of our own species when they have arrived at that age when they are always in mischief, and when, according to the notions of a past generation, they were always to be cuffed, because, if they did not deserve it at the time of the infliction, they soon would do so.

name.

They are of various sizes, but so arranged as to form a beautifully regular pattern; for each plate has at its centre a large boss, and, as the plates are regularly placed one above the other, there are, on the whole shell, twenty rows of these tubercles running from top to bottom, set on lines which correspond to the meridians of a globe. Yet, if the reader has followed the description, he will see that these rows are not all at equal distances from one another, for those on the smaller perforated plates are approximated, while those of the larger plates are removed from one another; nor are the tubercles of the several rows all at the same distance from each other. Besides these tubercles, a great many others of very various sizes lie between the rows. The whole effect of the pattern is very beautiful, and shows that symmetry without sameness, that unity in variety, with which all the works of God abound, and which the architect and the designer are so perpetually striving after, but to which they so seldom attain.

The ten perforated tracts which, being arranged in pairs, form five double bands or courses, converge towards the mouth and anus. The regularity of these tracts, converging at both ends and leaving between them a solid tract, has suggested a fanciful analogy. They were thought to resemble the gravel walks of our gardens, with their borders or avenues of trees on each side, and so were called ambulacra; ambulacrum being a post-classical Latin word, meaning a garden walk. At the point where the two converging perforated tracts unite, is a single six-sided solid plate, which has at its side nearest the ambulacra a hole from which the ambulacral holes seem to diverge. The five perforated hexagonal plates which thus stand at the end of the ambulacral avenues, are separated from one another and from the top opening by five other irregularly eight-sided plates which surround the small movable scales which cover in the anus. As far as our previous description has gone, the reader will perceive that all the parts are perfectly radial. The five segments are absolutely alike; but one of the eight-sided plates has, between the large pore and the anus, a space which is full of a great multitude of holes, and in this respect it differs from all the other five plates of the series, and is called the madreporic plate. At the other pole of the body there is a large opening covered by a leathery membrane, in the centre of which is the mouth. Placing the animal with its mouth downwards, which is the position it usually occupies, and looking at it from above, let us enumerate the perforations which we have described, beginning from the centre at top, and proceeding outwar!enl

downward, so that all confusion may be avoided. We have the following different series :

:

1. The central round opening, which is covered by small movable calcareous pieces, called the apical hole.

while the ridges between the grooves, stretching further inward than the furrows, form saw-like edges, so that after the food, mixed with hard particles, has passed the tips of the teeth, it can be ground down to a fine pulp by these triturating

2. On one side of this are the minute crowded holes of the edges and surfaces. madreporic plate.

3. In the five plates which surround the apical hole are the five holes, each of which occupies the external angle of its plate; these are called the generative pores.

4. In the five plates which are intermediate to and outside these the ocular holes are seen.

5. Stretching away in five double tracts are the ambulacral holes.

6. The large opening below for the mouth and its membrane. We are now in a position to indicate the relation of the soft parts of the animal to this protective box. All the above named perforations have their uses; and a study of these will teach us almost the whole anatomy of the animal.

The alimentary canal connects the two largest holes which lie in the vertical axis of the body. The entrance, or mouth, is in the centre of the wide orifice in the under side, which is covered in by a leathery membrane, with the exception of where the pointed teeth project. The curious beak, composed of five sharp teeth, forms a very effective instrument wherewith the animal can scrape away the soft, calcareous rocks in which so many worms and sea-animalcules bore and hide themselves. It is supposed that the animal swallows chalk and animals together, and lives on the nutritive, organic substances, while the chalk, etc., are passed out again, just as in the case of the earth-worm, great quantities of soft vegetable mould are swallowed for the sake of the nutriment it contains in the shape of particles of leaves, etc. The protruded part of the beak, how ever, gives no idea of the very complex machinery by which these teeth are worked from within. If the leathery membrane be cut round close to the shell and pulled out, it brings with it, or allows to be abstracted, a large and complicated hard framework in the form of a five-sided pyramid, with its base upward, and its apex formed by the teeth. This pyramid consists of five jaws, each of which is a frame which sustains the tooth, and has attached to it the muscles which move this tooth in all required directions. The jaw being hollow allows the tooth to enter at its upper broader side, and to pass down in a groove which becomes closely applied to the tooth on all sides at the lower end, and so holds it in a kind of socket, in which, however, it can move downward, as the tooth is worn away below, and is supplied from above. The tooth consists of a curved and flattened bar, ending in a point, and having on its inner side a flange to strengthen it, which flange stands out at right angles to the flattened inner surface of the tooth. The tip of the tooth is of enamel-like hardness, but as you trace it up through the jaw, it becomes softer and softer, until it is found to be quite without hard deposit at the part where it protrudes above the jaw. This shows that there is a process of continual renewal, the tooth being laid down as a gelatinous substance in which more and more hard, earthy salts are deposited as it is pushed forward, until it consists almost wholly of these, and is fitted to cope with the hard material to the rasping of which the animal applies it.

Round the base of the pyramid runs a pentangular muscle, which binds the jaws together. From the outer side of the base of each jaw run muscles to the shell at the sides of the orifice of the mouth. These, when contracted, protrude the teeth all together from the mouth. Other muscles unite the sides of the jaws to one another, and these, when contracted, bring the teeth together. A series of long pieces attached to the centre of the base of the pyramid, gives attachment to muscles, which, running to the shell, have the function of approximating the tips of the teeth. In order to retract the whole apparatus when acting together, or to pull away each separate tooth from the rest when acting separately, a number of muscles (two for each tooth) run from the lower end of the jaw to some calcareous loops or arches, which, standing on the sides of the oral hole, rise up within the shell.

The food canal does not run in a straight line from mouth to anus, but, after proceeding a short way as a contracted throat, opens sideways into a wider canal, which, after winding once round the inside of the shell, is bent on itself, and winds round back again, and then delivers at the apical hole. This winding enables the food to undergo a more thorough digestion, while the nutritive parts of the food are dissolved, and either pass into the blood-vessels, which are found in the walls of the intestines, or into the surrounding cavity. It must not be supposed that this long alimentary canal is loose in the box, only attached by its two extremities. If so, it would be liable to become entangled. It is attached by a membrane which lines the inner surface of the shell, and then passes off from this round the alimentary tube, so as to hold it in a loop, or rather fold. This arrangement is very general, not only in these, but in the higher animals.

The holes in the five larger plates surrounding the anal opening are those through which the eggs are extruded (in the case of the female) into the sea-water, so to renew the round of life. They furnish the exits for five separate organs situated just below them. The holes in the alternate plates are called ocular holes, because, through them, a nerve passes to an organ, supposed to be an eye. The ambulacral holes and the madreporic holes need a further explanation, which will lead to a description of the locomotive organs of the animal. The locomotive organs of the echinus are of two kinds-the soft for pulling, and the hard for pushing. The hard-pushing organs are the spines. These are, no doubt, defensive organs, but they also unite with this function that of locomotion. The spines are, as we have said, set upon the knobs of the outside of the shell. They are, however, movable upon these, so that they can be turned in all directions. To effect this movement without destroying the solidity of their attachment, there is a curious contrivance. At the centre of the concave base of the spine, there is (at least in the purple-tipped sea-urchin) a pit corresponding to the pit in the centre of the tubercle on which it is set. A ligament runs from one pit to the other, and so prevents the spine from slipping off its support, while from the edges of the base of the spine muscular fibres run to the membrane which clothes the shell. It will be seen from this that the shell is not naked, but covered with irritable and live membrane, which membrane passes down between each plate, and, no doubt, subserves the function of secreting fresh matter round the edges of these plates as the animal grows. How far the spines may aid the animal in progression may be a matter of question; but those who have observed its motion believe they are concerned in it. By far the most efficient organs of locomotion are the little tubular feet ending in discs, which are protruded through the ambulacral holes. These feet act like suckers, when ap plied to the rock on which the animal moves. The coatings of circular and longitudinal muscles which enclose the hollow tubes are sufficient to move the animal when a multitude of these discs have been extended and attached; but the question arises, how are they protruded? This is done by a curious contrivance. Each little tube, after traversing the shell and arriving at the interior, expands into a muscular bag. Both bag and tube contain liquid. All the little bags, set on each line of ambulacra, communicate with a vessel, which stretches from mouth to anus, and these ten vessels all communicate with a ring round the mouth, which ring has, opening into it, some larger bladders to contain a reservoir of water, and it also communicates with the madreporic holes by a tube, which is filled with fine sand. The method of protruding the tubular feet is supposed to be the following: sea-water is filtered through the madreporic plate and sand canal to the ring round the mouth. When the animal is in a lively state and inclined for locomotion, the bladders force the water into the rows of little bags, and these being muscular, can, by contracting, force out any or all of the sucking feet at pleasure. When, on the other hand, the animal wishes to retract all its feet, the bags, distended by receiving all the water which was in the tubes when extended, would be in an awkward state of tension, unless the fluid were allowed to pass back into the ring and bladders.