behold constitutes only a part of the animal creation. Besides those that are hid in the sanctuary of the forest, and the depths of the ocean, there are tribes which inhabit great caverns and subterranean waters, and that are specially adapted for dwelling in a world where darkness ruleth, and Light "never comes, that comes to all." And there are others,-and to these our attention is now to be directed, that escape our notice, either by their own minuteness or by their dwelling-place. To this unseen world of animal existence this chapter is to be devoted; it comprises two classes of Radiate Animals-the Infusory Animalcules, which the microscope brings before our eyes, and the Internal Parasites, that live hidden from observation within the bodies of other animals. activity, in a mountain spring at Lochnagar, Aberdeenshire, at an elevation of 37,00 feet; and at present we do not know the limit to their distribution. Among them there is great disparity of size; the difference between the smallest and the largest being as great, proportionally, as between a mouse and an elephant. But the exceeding minuteness of the smallest, though science can reduce it to measurement and calculation, baffles our finite faculties, as completely as the vast distances and magnitudes of the heavenly bodies revealed by the astronomer. The measurement of one minute species, (monas crepusculus), is said to be 2000 of a line. such infusoria, a space not exceeding that of a single drop of water may contain five hundred millions of individuals! Two such drops might, therefore, have a population far exceeding that of all the human races now living on the earth! Of We read of five hundred millions, and the words drop smoothly from our tongue, but how faintly does the mind take cognizance of the multitude expressed by those figures! I may mention, for the sake of some of my young readers, that the word "animalcule" means a "little animal;" and that the term "infusory has reference to their being easily procured by making an infusion of animal or vegetable matter, and allowing it to stand exposed to light and It may assist my young readers in formheat, such as the window of a sitting-rooming some idea of its extent, if they estimawould afford. If a drop of the thick scum that ted in what space of time the number of may after a few days have gathered on the animalcules could be actually reckoned. I surface, be placed between two plates of will suppose that the person counting them glass, under the microscope, a busy world works only six days in each week, that he of animated existence will be revealed to counts one in each second, and works view; and in that little film of water may twelve hours each day. At this rate it be seen hundreds of delighted creatures would take him thirty-seven years to comswimming about as freely as if disporting plete his task.† in an ocean. The scene that I describe is, in fact, going on beside me while I write; for the Christmas holidays have come, and happy boys and girls are busy round the table on which the microscope stands. Loud and frequent are their exclamations of astonishment, for not only do the animalcules swim between the plates of glass, but they swim one above the other, so that, compared with the size of their bodies, that little film of water has positive depth, as well as superficial extent. They are found, however, not merely in situations where decaying animal or vegetable matter would seem to supply them with food, but also in lakes, rivers, and even in wells of the purest water. They have been observed in great numbers, and in full Fig. 2. The first marvel about these diminutive * A line is the twelfth part of an inch. The exact period would be 37 years, 5 weeks, O days, 0 hours, 45 minutes, and 20 seconds. creatures is their size; the second is their numbers; the third-and to a reflective mind, perhaps the greatest marvel of the three is their reproduction. This is very diversified. Some appear like buds or gemmules, on the surface of the body of the parent, assume the characters of the species, drop off, and become detached and independent beings. Others, again, divide into two equal portions, by what is termed spontaneous fission or division, (Fig. 2.) The young exist in various states of progression, and undergo various changes, until they are able to swim about at large, select a new abode, put forth a new stem, and become the living parent of a fresh colony of bell-shaped blossoms-if such a term may be applied to a group of living animalcules. The fissiparous mode of reproduction is amazingly productive, and indeed far surpasses in fertility any other with which we are acquainted, not excepting the most prolific insects, or even fishes. Thus, the Paramecium aurelia, (which also propagates by ova,) if well supplied with food, has heen observed to divide every twenty-four hours; so that, in a fortnight, allowing the product of each division to multiply at the same rate, 16,384 animalcules would be produced from the same stock, and in four weeks the astonishing number of 268,435,456 new beings would result from a continued repetition of the process. Perhaps the Volvox Globator, of which a figure is annexed (Fig. 3), has excited by Fig. 3. its mode of reproduction, as much or more attention than any other species. The parent, to use the most popular and best understood expression, is a delicate green transparent globe, moving by means of minute hair-like bodies termed cilia, which cover the exterior surface. Smaller globes are seen in the interior, furnished with the same means of progression, and swimming freely about. At length the outer covering bursts, the young escaping through the fissure, enter on a wider sphere of existence, and yet, even at that moment, gemmules may be seen within them, which in like manner are destined to increase and come to maturity. Some authors regard the Volvox, not as a parent and its young, but as a compound animal; but this question is one that need not at present be discussed. Besides these modes of increase, the Infusoria have that arising from the deposit of ova, or eggs. As the ditches in which the animalcules live dry up in summer, they perish; but prior to this, the mature ova burst through the skin of the parent; and thus the last act of the creature's life is to provide for the continuance of the species, by depositing thousands of fertile germs. These are lifted up by the winds which scatter the dust-they are dispersed through the atmosphere-and float in the air, ready to assume the functions of active life, so soon as they are placed in circumstances favourable to its development. In the Paramecium already mentioned, the eggs are excluded in masses. These are developed into young with great rapidity; these again lay eggs, not singly, but in masses; so that in two or three days, their number surpasses calculation. That particles of unorganized matter can, under any combination of circumstances, be converted into living atoms, such as these animalcules, is an opinion that has at times gained some degree of currency, but is altogether erroneous. The elaborate provision made for the continuance of these races, by the diversified modes of reproduction which have just been detailed, renders superfluous the theory of equivocal generation; and adds another proof to those we see everywhere around us, that the little and the great, as we are pleased to call them, are alike under the providential care of ONE, in whose eyes such differences are of no account. It is unnecessary to dwell long upon the classification of the Infusoria. They have been divided by Ehrenberg into two great groups, comprising several genera: one group is distinguished by numerous internal sacs, or stomachs, (see Fig. 4,) as he regarded them; hence he gave them the name Polygastrica, or "many-stomached." tunate Polygastrica that come within the The sacs or stomachs he rendered visible vortex. Twice have I now been summoned by dissolving some carmine or indigo, and placing it in the water with the animalcules; as they fed, the food deposited in these curious receptacles became apparent. This group contains those that are most diminutive in size, and most simple in structure. They are furnished with the little hair-like bodies called cilia, already mentioned, and by their action are impelled through the water, in which they find those nutritive particles on which they subsist. Some, I regret to say, indulge cannibal propensities, and contrive to gulp down a fellow animalcule almost as large as themselves. Their movements would seem to be unaccompanied by fatigue, for it continues both by night and by day; and, like our breathing, or the circulation of our blood, seems not to depend on any act of volition. Fig. 5. to lay down my pen, and witness the process. They have, for the better mastication of their prey, a singular_apparatus of teeth, if it may so be called. It has been likened to an anvil, with a hammer on either side. These hammers can be brought into action in a moment: they must be very effectual implements, and are vigorously wielded. The rate of increase among the Wheel animalcules is greater than we know of among any other animals--their manystomached relatives alone excepted. As an The other group is of much higher struc- example, the Hydatina senta may be menture, so much so indeed, that their removal tioned. Ehrenberg, we are told, watched to the class of Articulated Animals has been during eighteen days successively, an indisuggested. They have lobes surrounding vidual which was full grown when singled the mouth; these lobes are fringed with out, and did not die of old age, which proves cilia, which by their movement give to these this species to live more than twenty days. parts the appearance of wheels in rapid In from twenty-four to thirty hours, this motion. Hence, Ehrenberg bestowed on animalcule will deposit four ova, which them the name Rotifera, or "wheel-bear-will grow from the embryo to maturity, and ing." They can swim either slowly, or with considerable swiftness, in pursuit of their prey. Most frequently, however, they take matters very quietly, like gentlemen "who live at home at ease;" for, fixing themselves by the pincers shown in Fig. 5, they bring the cilia round their mouths into play; these cause currents in the water, Their tenacity of life is scarcely less reand thus enable them to devour the unfor-markable than their numbers. They may bring forth their fertilized ova in the same period. An individual producing in ten days forty eggs, developed at this rapid rate of increase, would have on the tenth day one million of descendants, on the eleventh day four millions, on the twelfth day sixteen millions, and so continue to multiply. he dried up until apparently dead, and again | rays of the sun, but at night the watery revived by the application of moisture. vapour being removed by the frost Fontana kept some of them two years and a half in dry sand, exposed to all the power of an Italian summer's sun; yet in two hours after the application of rain water, they recovered life and motion. When we muse upon this lowly region of animal life; reflect on the strange powers of increase with which its microscopic population is gifted, and the powers of endurance they possess-we cannot but be struck with the Providential care that preserves them from destruction, and insures the continuance of the various species. And we may fairly infer that they serve important purposes, though we. can but faintly trace them out. We cannot, however, err in saying, that by their feeding upon the decaying particles of organized bodies, they effectually assist in maintaining the purity of the waters; while at the same time, as their vast numbers compensate for their minute size, they furnish a large supply of food to other creatures dwelling therein. "The full ethereal round, Infinite worlds disclosing on the view, Shines out intensely keen; and all one cope Of starry glitter, glows from pole to pole." The birds, which at other times found a plentiful supply of food in the open fields, find everything frozen and congealed into hard masses. The seeds and berries which were formerly accessible to their horny beaks, are so no longer, owing to the freezing of the water in the ground, or the snow which hides their food. Hence the feathered tribes are driven by hunger to approach the dwellings of man, where the heat generated by fires, and radiated from his habitations, tends to thaw and soften the ice-bound surface around, and whence unfrozen nutrition is continually thrown at the doors. The wild fowl, driven from the chilly north, where the streams on which they were wont to swim are no longer liquid, take a southward flight, and in flocks of singular shape astonish the observer. The circumstance upon which these actions depend is the liability of water, when deprived of a certain amount of heat, to pass TERRESTRIAL PHENOMENA OF from the state of vapour or fluid to the THE MONTHS. JANUARY. "All Nature feels the renovating force Deriv'd, thou secret all-invading power And seizes Nature fast. It freezes on, the frost-work fair, Where transient hues and fancied figures rise." solid form. Snow is watery vapour suddenly congealed, while ice is liquid water frozen. In passing from the liquid to the solid form, water is a remarkable exception to the law that all bodies expand when heated, and contract when cooled; inasmuch as water, after cooling to a certain degree, begins to expand, and continues to do so till it is changed and becomes ice. To illustrate the general law :-Fit exactly a rod of iron, when cold, to a hole iron, and you will find that you will be in a piece of metal or stone, then heat the unable to make it enter the aperture which previously admitted it. Again, having heated a bar of iron to redness, take it from the fire, and lay it upon the flag-stones, or on a brick floor, and place close to either THE most striking phenomena of the end of the bar a brick or other body having season are known to us under the names a plain surface, which will fit against the of FROST and SNOW. At this season it is extremity of the piece of iron; if you wait usual to find the brooks-which lately prat- a few moments, till the bar is cold, you tled a mournful music amidst the naked will observe that there is an interval betrees, and bore upon their bosom towards tween the ends of the bar and the surface the ocean the brown leaves of autumn- of the bricks, which did not exist when the sealed up and congealed into silence. bar was hot. All substances, except water, During the day a haze obscures the oblique | thus expand with heat, and contract with cold. But what is Cold? and what is Heat? Heat is a peculiar influence of a positive character, which can only be judged of by its effects upon matter; Cold is negative heat-the absence of warmth. We can only judge of heat by its effects, and we are accustomed to measure its intensity by the power which it possesses to expand some substance exposed to it. Thus, in the common thermometer we use the liquid metal mercury, to indicate the heat of a hot bath, or of the temperature of a room, because we know that mercury is expanded by heat, and contracts if heat be removed. The degree of contraction under similar influences varies in fluids, but not in gases. Chlorine, hydrogen, oxygen, carbonic acid, &c., are equally affected by exposure to heat, but alcohol is affected six times as much as quicksilver, and lead will expand under the same circumstances, three times as much as iron. But to this general law of expansion by heat, and contraction by its removal, water is a remarkable exception. Procure a Florence flask, (which may be purchased for a few pence at any of the oil-shops) and pour some water into it till it is nearly filled, marking with a file upon the neck the exact height at which the fluid stands. In a deep basin or jar, provide a freezing mixture, composed of snow, (or broken ice) and salt, in which let the flask be buried up to the neck. If the water which you have poured into the flask be above 40 deg. of Fahrenheit's thermometer, (as it will be if it has been kept in the house for a few hours before using) you will observe that it begins to contract till it is reduced to that temperature, when it will begin slowly to expand, and continue to do so till the fluid passes into the solid state. The increase or diminution of the volume of the water will be indicated by a rising or falling in the neck of the flask. To render this experiment complete, a small thermometer should be placed in the water, to indicate the changes of temperature, so that the observer may note with accuracy the corresponding alterations. From this experiment we learn that the greatest density of water is attained at a temperature of 40 deg., and that whether heated above that temperature, or cooled below it, the expansion will be similar. At 48 deg. the water will occupy the same space as its ice at the temperature of 32 deg. If we take a bottle quite full of water, at the temperature of 40 deg., and close it so that no fluid can escape, the bottle will be burst by exposure to heat or to cold; for both would increase the volume of the liquid. From this it follows, that ice is lighter than water at any temperature below 48 deg. of Fahrenheit's thermometer, and it will be shown that this increase of volume produced under the influence of frost, is a most beneficial arrangement of the Divine Ruler of all things. If water, like other liquids, continued to contract and to increase in density until it assumed the solid form-our lakes and large bodies of water, instead of being superficially frozen in winter, would be hardened into solid masses of ice. The heat from the lake is abstracted by the cold winds which blow over its surface; and the chilled particles being more dense would descend, allowing other and warmer portions of the water to rise and be exposed to the frosty air, till the whole mass of the water was reduced to 32 deg. when it would suddenly freeze-to the destruction of most of the living things therein. But this is prevented by the phenomenon of which we have been speaking; for, as soon as the whole mass is cooled down to 40 deg. there is no changing of position in the particles, since those on the surface which are rendered colder now become lighter than their fellows; so that the cold water actually floats upon that which is comparatively warm. Water being a bad conductor of heat, the warmth of the lower stratum is not removed, though the surface may be a sheet of ice. Moreover, ice being also a non-conductor, the cold winds may continue to blow without avail; since the deep strata of water are protected from cold, and remain at the temperature of 40 deg. whatever may be the cold of the surrounding * This freezing mixture is most active in the following proportions:-Snow, or pounded ice, two parts; salt (known to the chemist as muriate of soda) one part. Ice can be purchased from most of the confectioners at all periods of the year, but should there be a difficulty in procuring it, the following freezing mixture may be used:Muriate of ammonia, five parts; nitrate of potash, five parts; sulphate of soda, eight parts; and air. To make this evident to the eye, the water, sixteen parts. following experiment has been suggested: |