characters in history that are teaching us this folly of neglect, foremost there stands Ethelred the Unready, who did not lack opportunities for success, but was simply unprepared for them. The Persians have a saying, "A stone that is fit for the wall is not left in the way;" but then the stone must be fit, and those who are to find their place of honour in the fabric of society must not mind the toil and pains of being prepared for their place, assured that they will not be left neglected by the wayside. In all civilised states it is not that there are too many ready for superior posts, but that there are few well prepared when the morning of opportunity comes. The young student of German or French, as he ponders the lessons in the POPULAR EDUCATOR, may see no direct connection between these studies and his future advancement; but it may so happen that an opening will occur in some future day in which even mercantile partnership or commercial success may depend upon his acquaintance with these or other Continental tongues. Patience, then, does not imply idleness, but steady plodding in the path of preparation while waiting for the dawn of opportunity's day. Differences of constitutional temperament will doubtless affect the exercise of this virtue, but all men may be schooled to its exercise in matters of common life. Some persons are impatient of contradiction-some impatient of precedence-some impatient of attention, even in matters of dress or diet. Impatience is selfishness in a hurry, and needs check and control in its very earliest manifestations. "Teach them to wait," is counsel as appropriate to the young as "Teach them to work." No virtue has a stronger influence in its operation over other minds than that of patience; we learn not only to respect but to imitate. Steady and patient endurance in an hour of danger not only honours us, but saves the lives of others; whereas hot and heady conduct, in its foolish rashness, is ruinous often to the interests of those with whom we may be associated.

Many of the scientific successes of later days have been marvels of patience-not only the bridging of straits, which more properly may be considered as belonging to perseverance, but the steady and slow induction of facts which have taken place previous to the adoption of any new principle of action.

Patience is always a characteristic of power. Strong minds can afford to wait. It is the sign of weakness to be subject to panic in the presence of some unexpected difficulties, or to be determinately pushing on some enterprise, regardless of the wisdom of the course pursued.

The student of military campaigns will see that success has oftener resulted from patient endurance than from brilliant charges; and that the statesmen who have carried the most decisive measures have been men also who did not try to hurry their party into action, but calmly adopted the appropriate method, and waited the appropriate time. Patience is of essential importance to all the other virtues of character. Indeed, it is so necessary to their health and culture, that without it they shoot up into hasty and weedy growth. Those characters blossom best that have had time to let the roots of principle strike deep down into the soil.

Apart, however, altogether from issues of success, patient endurance is noble and beautiful; and as life is a state in which we must all look for checks and hindrances to our most cherished purposes, we shall be ill prepared to act well our part in the common arena of life unless we cultivate a patient spirit. In any system, therefore, of moral science which is to be adapted not only to man's mental and moral constitution, but to his earthly condition, there must be a place found for the principle of an earnest and intelligent patience.

LESSONS IN ARITHMETIC.-XXVI.
COMPOUND SUBTRACTION.

5. THE process of finding the difference of any two compound quantities of the same kind is called Compound Subtraction.

This is performed upon the same principle as simple subtraction-namely, that the difference between any two quantities is not altered by adding the same quantity to each.

EXAMPLE. From £25 98. 74d. subtract £14 17s. 9 d. Write the less quantity under the greater, with the corresponding denominations under each other, and express, for clearness, the farthings in a separate column.

Three farthings cannot be subtracted from 1 farthing. We

10 11 9 2

therefore add 1 penny, or 4 farthings, to the 1 farthing of the upper quantity, and 1 penny to the 9 pence of the lower quantity. Then 3 farthings subtracted from 5 £ s. d. far. farthings leave 2 farthings. Again, 10 pence 25 9 7 1 cannot be subtracted from 7 pence. We therefore 14 17 9 3 add 1 shilling, or 12 pence, to the 7 pence of the upper quantity, and 1 shilling to the 17 shillings of the lower quantity. Then 10 pence subtracted from 19 pence leave 9 pence. Again, 18 shillings cannot be subtracted from 9 shillings. We therefore add 1 pound, or 20 shillings, to the 9 shillings of the upper quantity, and 1 pound to the 14 pounds of the lower quantity. Then 18 shillings subtracted from 29 shillings leave 11 shillings; and 15 pounds subtracted from 25 pounds leave 10 pounds. £ s. d. far. 25 29 19 5 3

15 18 10

10 11 9 2

We have, in fact, subtracted the less of the annexed two quantities from the greater, and they are obtained by adding (as it will be found by examination we have done) £1 1s. 1d. to each of the quantities originally given. Hence we get the following

6. Rule for Compound Subtraction. Write the less quantity under the greater, so that the same denominations stand beneath each other. Beginning with the lowest denomination, subtract the number in each denomination of the lower line from that above it, and set down the remainder below. When a number in the lower line is greater than that of the same denomination in the upper, add one of the next highest denomination to the number in the upper line. Subtract as before, and carry one to the next denomination in the lower line, as in simple subtraction. 7. ADDITIONAL EXAMPLE. Subtract 75 gals. 3 qts. 1 pt. from 82 gals. 2 qts. gals. qts. pts. 82 2 0 75 3

6 2

1

Here, there being no pints in the upper line to subtract the 1 pint of the lower line from, we add 1 quart-i.e., 2 pints to the upper line, and the same quantity to the quarts 1 Ans. of the lower line. Then 1 pint subtracted from 2 pints leaves 1 pint. 4 quarts cannot be subtracted from 2 quarts. We therefore add 1 gallon-i.., 4 quarts-to the 2 quarts of the upper line, and 1 gallon to the 75 gallons of the lower. Then 4 quarts subgals, qts. pts. tracted from quarts leave 2 quarts; and 76 82 6 2 gallons subtracted from 82 gallons leave 6 76 4 1 gallons. The operation we have really performed is the subtraction of the less of the 6 2. 1 Ans. subjoined quantities from the greater, and they are obtained from the original two quantities by the addition of 1 gal. 1 qt. to each.

Find the difference of

EXERCISE 44.

1. £48 17s. 6d. and £37 14s. 93d.

2. £1,000 and (£500 6s. 7 d. + £496 78. 6d.)

3. 16 cwt. 3 qrs. 15 lbs. and 8 cwt. 2 qrs. 8 lbs. 6 oz.

4. 85 tons 16 cwt. 39 lbs. and 61 tons 14 cwt. 68 lbs.

5. 69 m. 41 r. 12 ft. and 89 m. 10 r. 14 ft.

6. 17 leagues 2 m. 3 fur. 4 r. 4 ft. and 19 leagues 1 m. 2 fur. 15 r.
7. 85 bush. 2 pks. 4 qts. and 49 bush. 3 pks. 6 qts.
8. 115 qrs. 3 bush. 1 pk. and 95 qrs. 4 bush. 3 pks.
9. 85 yds. 1 qr. 2 nls. and 29 yds. 2 qrs. 3 nls.
10. 100 yds. and 55 yds. 2 qrs. 1 nl.

11. 140 acres 17 rods and 54 acres 1 rood 18 rods.
12. 465 acres 48 rods and 230 acres 1 rood 30 p.
13. 446 cubic ft. 75 in. and 785 cubic ft. 69 in.
14. 30° 55′ 15′′ and 55° 58′ 30′′.

15. 71° 10' and 36° 6' 30".

Hence we see the truth of the following 9. Rule for Compound Multiplication. Multiply each denomination separately, beginning with the lowest, and divide each product by that number which it takes of the denomination multiplied to make one of the next higher. Set down the remainder, and carry the quotient to the next product, as in addition of compound numbers.

Obs. Any multiplier is of necessity an abstract number. Two concrete quantities cannot be multiplied together. Multiplication implies the repetition of some quantity a certain number of times; and we see, therefore, that to talk of multiplying one concrete quantity by another is nonsense.

In the case of geometrical magnitudes—in finding the area of a rectangle, for instance-we do not multiply the feet in one side by those in the other, but we multiply the number of feet in one side by the number of feet in the other, and from geometrical considerations we are able to show that this process will give us the number of square feet which the rectangle contains. The very idea of multiplication implies that the multiplier must be an abstract number. It is of the nature of twice, thrice, etc. (Vide Obs. of Art. 7, Lesson XXII., Vol. I., page 380.)

10. ADDITIONAL EXAMPLE IN COMPOUND MULTIPLICATION. Multiply 12 lbs. 3 oz. 16 dwts. by 56.

In a case like this, where the multiplier exceeds 12, it is often more convenient to separate it into factors, and to multiply the compound quantity successively by them (Lesson VI., Art. 2, Vol. I., page 95). Now 56 = 7 x 8.

1. £35 6s. 7d. by 7.

2. £1 6s. 8d. by 18.

3. 1 ton 270 lbs. by 15.

4. 16 tons 3 cwt. 10 lbs. by 25 and 84.

5. 17 dwts. 4 grs. by 96.

6. 15 gals. 2 qts. 1 pt. by 63 and 126.

7. 175 miles 7 fur. 18 rods by 84, 196, and 96. 8. 40 leagues 2 m. 5 fur. 15 r. by 50, 200, and 385. 9. 149 bush. 12 qts. by 60, 70, 80, and 90. 10. 26 qrs. 7 bush. 3 pks. 5 qts. by 110 and 1008. 11. 150 acres 65 rods by 52, 400, and 3000.

12. 70 yrs. 6 mo. 3 wks. 5 d. by 17, 29, and 36.

13. 265 cubic ft. 10 in. by 93, 496, and 5008.

14. 75° 40′ 21" by 210, 300, and 528.

15. £213 5s. 6d. by 819 and by 918.

16, 5 tons 15 cwt. 17 lbs. 3 oz. by 7, by 637, and 763.

17. £13 78. 9fd. by 1086012 and by 1260108.

LESSONS IN GEOGRAPHY.-XVI. HAVING explained, in a previous Lesson (see Vol. II., page 4), the nature of the seasons arising from the annual motion of the earth in its orbit or path round the sun, and the parallelism of its axis, or the invariable inclination of that axis to the plane of its orbit, we shall render this subject more strikingly evident by means of the accompanying diagram of the seasons. Here the sun is considered to be fixed at the point F in Fig. 4 (page 80), which is considered to be the focus of the elliptical or oval orbit in which the earth moves, and which is so near to the centre of the curve that it may be, on this small scale of figure, reckoned the same with that centre; and you know that the centre is the point where the major axis, between summer and winter, intersects or crosses the minor axis, between spring and autumn. If you are curious enough to know how far the focus, F, is from the real centre of the orbit, we shall tell you; it is about onesixtieth part of the half of the major axis, or of the mean distance between the earth and the sun, from the real centre. Let us see if we can express this distance in some known measure. The mean distance of the earth from the sun, or the length of the mean semi-diameter of the earth's orbit, is about 23,109 times the length of the mean terrestrial radius, or of the mean distance from the centre of the globe of the earth to its surface. The earth's mean radius is 3,956 British miles, its mean diameter being 7,913 miles. Therefore multiplying 3,956 miles by 23,109, we have the mean distance of the earth from the sun, that is, half the major axis of its orbit, about 91,431,000 in round numbers. This makes the mean diameter of the earth's orbit about 182,862,000 miles, and its approximate circumference about 574,709,000 miles. The linear eccentricity of the earth's orbit being 0168, or about one-sixtieth of its semi-axis major, or mean distance of 91,431,000 miles, we have 1,523,850 miles for the distance between the centre of the orbit and the centre of the sun, or the focus of that orbit. Consequently, the earth is about double this distance, or 3,047,700 miles nearer to the sun in winter than in summer.

In Fig. 4, the earth is represented in four different positions (momentary positions) in its orbit; namely, at mid-summer, midspring, mid-winter, and mid-autumn. In all these positions, as well as all round in its various positions in the orbit, the parallelism of its axis, N s, is preserved. This axis is inclined to the plane of the orbit, as we have before observed, at an angle of 66° 32'; hence it makes an angle of 23° 28′ with the perpendicular to the plane of its orbit; for the perpendicular, represented by the dotted line passing through the centre, o, makes an angle of 90° with the plane of the orbit; and subtracting 66° 32′ from 90° gives the remainder 23° 28', which is the angle between the axis, N s, and the perpendicular, or dotted line. By reason of this parallelism of the axis N s, it so happens that at mid-spring, or March 20th, the half of the globe is illuminated from pole to pole, that is, from the northern extremity of the axis N, to the southern extremity of the axis s, and the days and nights are then exactly equal all over the earth; that is, there are twelve hours of light and twelve hours of darkness to every spot on the earth's surface for this day. Hence this day is called the equinox (equal night) of spring, or the vernal equinox. Again, at mid-summer, or June 21st, the half of the globe is illuminated from the circumference of a small circle of the globe at the distance of 23° 28′ from the north pole, N, to the circumference of a small circle at the distance of 23° 28' from the south pole, s; and the day is twenty-four hours long at all places of the earth contained in the space between the small circle and the north pole; that is, there are twenty

Vol. I., page 111.) ·

this space on this day; but the night is twenty-four hours long at all places of the earth contained in the space between the small circle and the south pole, that is, there are twenty-four hours of darkness and no light at all to every spot within this space on this day. As at this point the earth begins to return to a position similar to that at the vernal equinox, and the sun seems to be stationary as to its appearance and effects on the earth's surface for two or three days before and after this day, it is called the summer solstice (sun-standing), or the tropic (turning) of summer. Next, at mid-autumn, or Sept. 23rd, the half of the globe is again illuminated from pole to pole, and the same appearances take place as at the equinox of the spring, that is, the days and nights are then exactly equal all over the

earth, or there are twelve hours of light and twelve hours of darkness to every spot on the earth's surface for this day. Hence this day is called the equinox of autumn, or the autumnal equinox. Lastly, at mid-winter, or Dec. 21st, the half of the globe is illuminated from the circumference of a small circle of the globe at the distance of 23° 28′ from the south pole, s, to the circumference of a small circle at the distance of 23° 28' from the north pole, N, and the day is twenty-four hours long at all places of the earth contained in the space between the small circle and the south pole; that is, there are twenty-four hours of light and no darkness at all to every spot within this врасе on this day; but the night is twenty-four hours long at all places of the earth contained in the space between the small circle and the north pole;

would pass through c, the centre of the sphere. Every circle, whose plane thus passes through the centre of the sphere, is called a great circle of the sphere. It is further evident that every point, such as M, on the surface of the sphere, will describe a circle smaller than the circle E Q in proportion to its distance from the point E on either side, or to its vicinity to either of the points P P; and that if the sphere were cut by a plane or flat surface, like an orange by a knife, through such a circle as M S, it would not pass though c, the centre of the sphere. Every circle whose plane does not pass through the centre of the sphere, is called a small circle of the sphere. Accordingly, the circles M s and TN are called small circles of the sphere; and if the points M and T be equally distant from the point E, these circles

SPRING.

N

MARCH 20.

P

the illuminated half of the globe, because from the representation of its position it is turned in front both to the sun at F, and to you the spectator; at the summer solstice, or June 21st, you see only half of the illuminated half of the globe, because it is turned in front to the sun at F, but only sideways to you the spectator, you being outside of the orbit; at the autumnal equinox, or Sept. 23rd, you see none of the illuminated half of the globe, because it is turned in front to the sun at F, but at the back to you, the spectator, you being outside the orbit and as it were behind the globe; and at the winter solstice, or Dec. 21st, you again see half of the illuminated half of the globe, because it is turned in front to the sun at F, but only sideways to M you, the spectator, for the same reason as before. But were you placed in the middle of the orbit at the point F, you would, by turning round and round to the different points of it we have been describing, see the whole of the illuminated half of the globe at each point; and were you placed outside of the orbit in the directions of the major and minor axes, and made to look at the globe in these directions only, you would see none of the illuminated half of the globe, but only the dark side in each position.

E

R

P

E

S

will be equal in size, and their planes will cut the axis in two points

equally dis tant from the centre, c. The plane of a great circle, such

as E Q, cuts the globe or sphere into two hemiequal spheres; but the plane of

a small circle cuts it into two For some pur

unequal parts, or segments (cuttings) of a sphere. poses, the circumference of a circle, large or small, is divided into 360 equal parts, in order to enable us to measure distances along the circumference; each of these equal parts being called a degree; for other purposes, the circle is divided into two equal parts called semicircles, and these are also divided into degrees, each containing 180 degrees, and both 360 degrees as before; and for other purposes still, the circle is

S

0

T

divided into four equal parts called quadrants, each containing 90 degrees, and the whole containing 360 degrees as before. Each degree is divided into 60 equal parts called minutes, and these minutes (minute parts) are employed to express any part or fraction of a degree which may be found over and above a certain number of degrees in any distance. Again, each minute is divided into 60 equal parts called seconds, and these seconds (second minute parts) are employed to express any part or fraction of a minute which may be found over and above a certain number of degrees and minutes in any distance; and so on, to thirds, fourths, etc. This division of the degree is called the sexagesimal (by sixtieths) division of the degree; the division of the quadrant of a circle into 90 degrees is called the nonagesimal (by ninetieths) division of the quadrant. The French, in some of their scientific works. adopt a different division of the circle and its parts. They divide the circle into 400 equal parts, calling them degrees; and of course, the quadrant into 100 degrees; also the degree into 100 parts called minutes; and so on: this is called the cente simal (by hundredths) division of the quadrant. Any number of degrees is marked by a small circle placed on the right of the number in a small character, and above the line; thus 27 denotes 27 degrees. Any number of minutes is marked by one dash from right to left, on the right of the number; of seconds, by two dashes, and so on; thus 10' denotes 10 minutes, 10" denotes 10 seconds, etc.

We must now explain the nature of some of the more important circles on the sphere or globe of the earth. If in Fig. 5, which we suppose to be a representation of the globe of the earth, P P denotes the axis-that is, the diameter of the sphere, passing through the centre, c, on which the sphere or globe revolves like a wheel on an axle-then it is evident that every point on its surface will, in the course of its revolution or whirling on its axis, describe a circle. Thus the points, M, E, and T on the surface, will describe the circles м s, EQ, and T N respectively; and it is evident that the point E, equally distant from the two points P P, the extremities or poles of the axis, will describe the largest circle of all in the course of the revolution; and that if the sphere were cut by a plane or flat anrface, like an orange by a knife, through the circle E Q, it

COMPARATIVE ANATOMY.-II.

DIVISIONS OF THE ANIMAL KINGDOM-VERTEBRATA-MOL

LUSCA-MOLLUSCOIDA-ANNULOSA-ANNULOIDA-CELEN

TERATA-PROTOZOA.

THE main divisions of the animal kingdom, called sub-kingdoms or branches, were first established on anything approaching a scientific basis by the great Baron von Cuvier. Previous classifiers had endeavoured to mark out these divisions by differences in some one organ or system of organs. The system which was generally made use of, as producing the most natural classification, was that of the organs of circulation of the blood, or the nutritive fluid which answered to the blood. The classification of animals according to the structure of their hearts, blood-vessels, etc., was perhaps as good as any founded on any one system of organs. At least, our great anatomist, Hunter, a

The three higher divisions remain very much as he constituted them. There could be no higher testimony to the value of these than this, that all the multitude of higher animals that have been discovered or examined since his time fall naturally under one or other of his divisions. Cuvier himself assigned some animals to the wrong branch, yet when the error was discovered it did not necessitate the formation of a new system, but merely a transference from one branch to another; and this proves conclusively that the classification was not an artificial system fitted on to his knowledge, which, though wide, was of course limited, but was a recognition of the fundamental plan of nature. 4 3

who had carefully examined all the systems of organs of animals in relation to their use in classifying, thought so. It now, how ever, seems to be laid down as a rule that it will not do to rely an any one character in classification. If a classification be made in dependence on the modifications of but one organ, it is sure to be an unnatural one. If, on the contrary, it can be stated that any group of animals is distinguished from the rest by peculiarities in two or more systems of organs, that group is sure to be a natural one. Cuvier was more successful than his predecessors, not so much because he had any better key by which to interpret the animal kingdom, as because he relied on no key, but trusting to his wide knowledge of the structure of animals, and to his sagacious perception of what similitudes or differences were fundamental and what were unimportant, he made a classification which recognised the plan of structure of each animal as a whole, that is, as made up of the sum of its organs. The difficulties attending such a method are far greater, the definitions of the branches thus formed are less simple and precise, than those of the former methods, but the results have the merit of being true to nature, and therefore stable.

The lowest of these branches, designated Radiata, has not maintained its ground as the others have, for the following reasons. Many of the animals assigned to this branch are microscopic, and had been but little examined, and Cuvier founded his branch on the plan of structure exhibited by some of the more conspicuous animals, such as the star-fish, and he assumed that all the lower animals conformed to that plan of structure. This, however, has been found not to be the fact. Nor was the definition of this branch good as far as it went, since it was founded on one peculiarity alone, namely, the plan of structure. In fact, however derogatory the admission may be to the great anatomist, we are compelled to admit that his sub-kingdom Radiata stands in the same relation to the rest of his admirable system, as the untidy lumber-room-which generally exists in even a well-ordered house, and into which everything which has no definite place of its own is thrown-does to the rest of the establishment. Most of us who make natural history collections of any kind, have in our cabinets a spare drawer, into which specimens we have not had time to examine or to name, or whose place in the collection we are doubtful

about, are placed. The contents of such a drawer are the measure of our ignorance, and when we are particularly fresh in spirit, or have much leisure, we open it with a confident expectation that a patient study of its contents will lead us to a further knowledge, and a truer and more complete arrangement. Such a drawer is Cuvier's branch Radiata, and men who have felt that Cuvier had forestalled all other anatomists in the arrangement of the higher animals into their main divisions, have been able to solace themselves by re-arranging the heterogeneous number of animals for which the star-fish and sea-urchin stood as the representatives in the mind of Cuvier.

Inasmuch as we must dismiss this branch Radiata from our system, and shall not be able to recur to it again, as we must to the other branches, it is, perhaps, as well that we should explain the character on which it was founded. Cuvier observed that while some of the higher animals have their two sides alike, yet they could be split down the middle in one direction only, so as to leave two exactly similar halves. Thus, if one of us were divided from the crown of the head vertically downward, so that the division passed through the mid-line of the back and also of the breast, we should be divided into two like halves; but if the vertical division were made in any other direction, the two halves; though they might be equal, would certainly be not alike. If, on the other hand, a star-fish be placed flat on a table, it may be bisected in more than one direction, and the halves would be alike. Indeed, if we wanted to divide it into like portions, we should naturally cut it into five or ten or more segments, beginning from the centre, and cutting outwards. The organs are not paired on each side of one plane, but arranged like the spokes of a wheel in diverging directions from a central axis. This plan of structure was therefore considered as the type of the branch Radiata, a radius meaning a line drawn from the centre to the circumference of a circle. If this radial arrangement of organs had been universal throughout this subkingdom, and were found in no other, this would have formed a well-marked division, but it is not so. Some of the organs of higher animals have an apparent radial arrangement, as, for instance, the hooklets by which intestinal worms fix themselves. In so-called radiate animals there is generally a two-sided arrangement to be found. Thus, while the arms of the seaanemone are radial, stretching away on all sides, its mouth has two lips and two corners. The common purple-tipped seahedgehog (echinus) is in outward form a typical radiate, but its near ally, the heart-urchin, is almost as two-sided as ourselves. We therefore reject this sub-kingdom, and substitute others in its stead, as will be seen in the sequel.

Instead of at once enumerating the numbers of sub-kingdoms of the animal kingdom, and appending to each a dry catalogue of the characters upon which they are formed, it is, perhaps, better to induce the reader to examine two animals belonging to two different branches for himself, so that he may remark the essential differences in structure which they manifest. Suppose, then, he procure a prawn and a stickleback, or, if he aim at larger specimens, more easily examined, he can obtain, as we have done, a lobster and a haddock. If these be carefully observed, first as to their external character, and then as to their internal organs, there will be found some points of similarity, but a great many points of difference.

Both are elongated animals, and both can be divided by a mid-vertical section into two similar halves. The outer covering of the fish, though it is covered with small scales, is thin and flexible. It offers but little resistance to pressure, and no firm support, or fixed point, from which muscles can play upon the limbs. It, moreover, manifests no tendency to division into segments or rings. Turning to the lobster, we find it is enclosed in a hard, inflexible armour, which is divided into segments or rings, placed one behind the other. This division is well marked and complete in the hinder part of the body, where there are seven hard annular pieces united by softer membrane. They overlap one another above, but are separated below. The great shield which covers the head and fore part of the body also consists of fourteen segments, but they have all become united. This thick, hard outer covering is the only solid part of the animal, and therefore to this must be attached the muscles at both ends; that is, both at the fixed point of support from which they pull, and also at the part of the body or limbs which they are intended to move. This arrangement is carried out even to the limbs, whose joints are likewise cased in separate hard

tubes, and which are wielded from within. Further, there is a manifest tendency for each segment of the body to have a pair of limbs. Thus, beginning from behind, we find on the last segment the limbs are not developed, but only indicated; but on the next they form the side lobes of the tail, and are the main instruments by which the lobster darts rapidly backward when alarmed. The next four segments have each paired limbs, consisting of two small fringed plates set at the end of a joint, and with them the lobster paddles quietly forward. Then comes a segment with a pair of limbs composed of two joints, used for other necessary purposes. Then under the great shield are the walking limbs, all many-jointed. Two pairs with one claw are preceded by two more terminated by small pincers; then come the formidable claws. Next come the foot-jaws and jaws. There are six pairs of these, placed closely one over the other, beneath the mouth; they cannot be seen in the engraving. Then come the pair of longer feelers, the shorter feelers, and finally the jointed eye-stalks. Thus each of the twenty-one segments of which the lobster's integument is supposed to consist has a pair of well-developed limbs, with the exception of the last. How utterly different is the locomotive apparatus of the fish! The necessary hard parts upon which the muscles must play are nowhere to be found on the outside. They are situated internally. Running through the centre of the body from snout to tail is a bony column or axis. This axis consists of pieces which are so closely united end to end that they support one another, but are capable of a slight motion on one another, so that the back-bone which they form can be bent and slightly twisted. This back-bone, ending forward in the base of the skull, is the main part of the hard skeleton which affords attachment to the muscles which move the limbs. In this case the tendency of each segment of the internal skeleton to produce limbs is so little marked, that there are not more than two pairs of paired limbs in all; and throughout this large subkingdom, which includes brutes, birds, reptiles, and fish, there are never more than this number found, though sometimes there is but one pair, and sometimes none at all. These limbs are not jointed hard tubes, pulled and moved by muscles running up the inside of them, but they are supported by bony levers, while the muscles act on them externally.

.

Passing on to the other systems of internal organs, we find a marked difference in the arrangement of the nervous, alimentary (food), and blood circulatory systems, in relation to one other.

In the lobster the nervous system consists of a double series of rounded masses called ganglions, which commence with two lying side by side (though partially united together) above the mouth, and in connection with the eyes, antennæ (feelers), etc. From these two cords stretch back, one running on each side the mouth or throat, to another double ganglion, and from this cords pass back which unite the remaining nervous masses together, all of which lie in a series along the floor of the tubular cavity of the body enclosed by the rings. Each ring has a double ganglion of its own, but these are sometimes united together, as in the lobster. The food canal runs from end to end through the centre of the body, and at its front extremity passes through the nervous tract (as we have seen), and opens on the under side of the body. The heart is situated above the food canal, and just under the hard covering of the back. We have, therefore, the main blood system situated above the food canal in the contre, and the nervous system below it; these two latter, however, crossing one another and exchanging places just at the front of the animal. All these structures are contained within one tube, which is the hard covering of the animal.

Contrasted with this arrangement is that of the fish. In this animal the food canal occupies the same central position, but the heart, instead of lying above it, lies on the under side. The nervous system does not consist of a series of knots, but of a continuous column, and it is contained not in the tube which lodges the other viscera, but in another tube, formed of bony arches springing from the back-bone, and which is super-imposed on the other tube. The relative arrangement is best understood by a reference to the illustration, where transverse sections are given, supposed to be taken from the parts of the animals where the lines marked ab cross the lateral views of the lobster and haddock.

The fish and the lobster, then, present two types of structure which are utterly different in many fundamental points, and if