mens are represented by colored figures, perfectly well done, and representing as correctly as can be wished, the brilliant exuvice of the mollusca, whose splendor and liveliness of colors, blending of shades, delicacy of structure and form, varnish of exterior, and pearly lustre of interior surface, in a great number of cases, would require more than an artist's pencil to give them the perfect appearance of nature. Upon this the author himself remarks in his introduction : "In this manual of conchology, we have endeavored to give a free translation of Lamarck's system, as simplified by De Blainville, and in order to facilitate as much as possible the study of this beautiful and interesting science, we have divided it into four classes- Annelides, Cirrhipedes, Conchifera, and Mollusca. To each class we have assigned its various families, to each family its genera, and to each genus its living species, thereby making it plain, and within the reach of the meanest capacity. A type of almost every genus is given, excepting only those shells which, from their similarity to other genera, may be easily classed." In a work "arranged for the use of students," and which treats of a subject "which has become one of the requisites of a finished education," we should have been pleased to see a somewhat detailed introduction upon the organization and classification of the shells, and the animals which inhabit them. It may be remarked, moreover, that the author having selected for his subject rather the class of shells than of mollusca, many of the latter must necessarily be excluded from his work. This is a great inconvenience, as will readily be understood, when we read in the introduction, "Painting draws from some of these animals many colors, valuable not so much for their beauty as their usefulness, as Chinese ink and sepia," and call to mind, that the sepia having no exterior shell, cannot be described in a treatise of conchology. 3. Die Infusions thierchen als volkommene Organismen. 4to. mit Atlas von 64 colorirten Kupfern. in Folio. Von C. G. EHRENBERG. Leipzig: 1838. THE descriptive part of this work is in French and Latin, and it is one of such importance in the history of nature, and as yet so little known among us, that we are induced to give a fuller account than common of the subject of which it treats. In presenting it to the French Academy of Sciences, at their meeting on the 27th of last August, M. de Humboldt made several observations upon the riches of the materials offered by the researches of Mr. Ehrenberg, which embrace the often complicated anatomy of the infusoria, their teeth, their digestive organs, made more evident by being fed upon indigo and carmine, their eyes, the traces of their nervous system, their geographical distribution on the globe, their connexion with the accumulation of silex and iron, their influence upon the production of humus, and upon the phosphorescence of the sea, considered as the effect of slight electrical discharges, etc. Mr. Ehrenberg had an opportunity of observing the different forms of infusoria beneath the surface of the earth in three continents-in Europe; in Africa, (Egypt, Nubia, Dongola, Abyssinia) during six years; in Syria, and in Northern Asia, whilst travelling with Mr. De Humboldt from the Caspian sea and the north of the Ural to the Altai and the province of Ili and Chinese Dzongaria. These vast countries contain many living species, which are found in millions in a fossil state in other latitudes, even on the other side of the equator. It is known to every one, that by the aid of the microscope, there may be seen in water which has been exposed for some time to the open air, minute animated beings, generally very transparent, and presenting an organization more or less simple. To these diminutive beings the name of infusoria has been given, because they are considered to be produced by the infusion of animal or vegetable matter in the water. The popular interest recently acquired by the solar microscope, and still more by the oxy-hydrogen microscope, induces us to believe that all our readers have sufficient knowledge of the microscopic animalcula, to be interested in the discoveries which have recently been made in the part of natural history, which relates to them. The number of species of these minute beings is far greater than would at first be imagined. In Professor Ehrenberg's recent magnificent work, figures of more than six hundred and fifty species of these animals are given. Among them many are covered with a shield or corselet, which Mr. Kützing, and afterwards Mr. Ehrenberg, and the celebrated chemist Rose, ascertained to be formed of silex. This discovery authorized the expectation that the fossil bones. of infusoria might be found, or, to speak more exactly, their remains deprived of animal matter, at the bottom of the ponds in which these creatures live in great numbers. It was, therefore, easy to credit the assertion of Mr. Fischer, when he announced that on the peat lands of Franzensbad, in Bohemia, he had just ascertained that a bed of siliceous matter found there in great abundance, was formed entirely of the corselets of infusoria. This discovery was made in 1836. A specimen of the same substance was examined the same year by Mr. Ehrenberg, and since then, the fossil infusoria have had a place in the scientific annals of every country. Since that time, numerous discoveries have been made by microscopic examination of different mineral substances. The fossils of Fischer might be regarded as in a somewhat recent state. But NO. VII.-VOL. IV. 29 when afterward, Mr. Ehrenberg, guided by his extraordinary spirit of investigation, discovered that polishing slate, semi-opal, silex, and some other mineral substances, were formed, in a great measure, of remains of the same nature, these immediately acquired a character of high antiquity. The greater part of the fossil species have their analogous species in fresh water, in the Baltic, and in the ocean. At different epochs, in the time of famine, the Laplanders have mixed a farinaceous mineral substance [bergmehl] with the flour of grain, to make bread. Examined with the microscope, this substance, which the Laplanders regard as a gift of the great Spirit of the Woods, is found to be composed entirely of fossil infusoria, more or less imperfectly preserved. It may give an idea of the diminutiveness of these animalcula, to state that this siliceous farina is as impalpable as wheat flour. In 1833, Berzelius, the distinguished chemist, analyzed this extraordinary substance, and discovered that it was composed of silex and animal matter, but it was not imagined by any one, that it was entirely formed of animalcula; that the ground from which it was taken was nothing but a vast cemetery, filled with the remains of an incalculable number of little animals that had ceased to exist centuries before. Lately, as was stated in the American Journal of Science and Arts, for October, these fossils have been discovered in great quantities in America, and their localities pointed out by Professors Bailey and Hitchcock. Many of the rocks which contain fossil infusoria, appear to have been exposed to the action of volcanic fires, without having undergone an alteration of form. This will be easily understood, when it is considered that pure silex is, of all substances, the one which longest resists the action of heat. The experiments made directly upon these mineral coverings of the animalcula by the learned Berlin naturalist, show us what an extreme heat they can bear without suffering any change. In marshes, there is annually found a deposit of a brown substance of an earthy appearance. This deposit is composed of animal and vegetable matter, and often contains the corselet infusoria. Heated in a porcelain oven, this substance becomes successively black and red. When in this last state, it exhibits, when examined with the microscope, the siliceous corselet, more or less perfect, and colored by the oxide of iron. Exposed to the tests of the most powerful acids, and of the alcalis, it does not dissolve, but the effect of the acid is to bleach it so thoroughly, that it acquires the perfect appearance of bergmehl. Exposed to the greatest heat which chemistry can produce, it manifests the beginning of fusion, probably from the silex not being completely pure. In the parts which are only heaped together by the heat, all the characteristics of form continue to be recognised. These observations may appear but little interesting to persons who require to see in every scientific discovery, a practical result. But minds which love to admire nature in the simple means which she employs to effect her object, will find in the foregoing, a grand subject of contemplation. Is it not astonishing, when the largest animals have often left but imperfect traces of their existence on our globe at very remote periods, that creatures so small as to be invisible without the aid of the finest microscope, should be heaped together and preserved for centuries in their original forms, when every thing around them has suffered the irresistible influence of time? Ought we not to acknowledge here, as in all other scientific discoveries, the wisdom of the creator? Instead of giving, as in the case of the mollusca, a thick shell, capable of leaving its imprint after its destruction, it gave to the infusoria an envelope indestructible by mechanical action, by reason of its thinness and of its hardness, and indestructible by time, by reason of its nature. In making choice of silex, the best material within our knowledge was chosen. Mr. Ehrenberg has specimens of all the substances in which fossil infusoria had been discovered. Beside those already cited, he has several varieties of bergmehl, which he gathered in the different saline waters of Germany. It appears that all salt springs contain animalcula in greater or less quantity. But the most remarkable part of his collection is, a series of specimens of living infusoria, with the siliceous corselets and their debris after they have been subjected successively to the action of heat and of acids. A very remarkable fact which results from the experiments of Mr. Ehrenberg is, that when the living infusoria are bleached by the process above spoken of, and exposed anew to a strong heat, they are again colored ochry red by the oxide of iron. This circumstance would seem to prove, that iron is found in the siliceous matter, in a state of combination unknown in chemistry. The most common kinds of infusoria are the navicularia and the bacillaria. The first has the shape of a weaver's shuttle; the second is nearly that of a discus; many of these discuses are sometimes found heaped up like piles of money. These infusoria, when alive, have not generally the active motions which commonly characterize the infusoria usually found in water; it would even be difficult to distinguish them from fossil infusoria, if they had not many cavities, colored green, which Mr. Ehrenberg considers as stomachs; and ovaries, which sometimes are largely developed. Another common form somewhat resembles the sole of a large shoe, that is, a very elongated oval; at each extremity is found an opening. This form is figured in the American Journal of Science, for last October. These three forms are very common * Ehrenberg calculated that polishing slate contained about forty-one thousand million of animalcula in a cubic inch. in polishing slate, in the siliceous substance of Franzensbad, and in the earthy deposite of Bilin. The property which the latter possesses, when it is well closed, of preserving alive the animalcula contained in it, has afforded Mr. Ehrenberg an opportunity of showing to the naturalists of Paris and London, the living infusoria and their debris reduced to fossils. The portion of this earthy matter which he has with him, has been kept in a tin box about eighteen months, without appearing to cause any injury to the diminutive beings enclosed in it. This work of Mr. Ehrenberg must now have great interest to to our own naturalists, from the discoveries daily making, of the same nature, in different parts of our country. 4. A Treatise on the Microscope. K. G. H., LL. D., F. R. S., etc. Black. pp. 193. By SIR DAVID Brewster, We wish to direct public attention to Sir David Brewster's treatise on the microscope, because it is so admirably adapted to give a clear idea of the means by which the most interesting discoveries have recently been made in that part of creation invisible to our unassisted organs of vision. This work, as its title fairly indicates, contains no theoretical observations upon the theory of light, or upon the manner in which vision is effected. The author, in the whole course of his treatise, is an adroit artist, who, under the eyes of the reader, constructs microscopes, at first very simple, afterwards more and more complicated, whilst he is at the same time instructing him how to make use of these several instruments. Among the simple microscopes which he mentions, that formed of a fluid lens deserves to be remarked, on account of the facility with which any one can construct it, even at the moment, when he wishes to examine a minute object. A drop taken on a pin's head from a glass of water, and placed in a small hole made in a piece of brass or other metal, forms then a kind of lens, and the smaller, the more perfect it is. By placing a drop of turpentine varnish upon a small plate of very thin and perfectly clear glass, a plane-convex lens is instantaneously formed; this will become double convex if another similar drop is put on the opposite face of the plate. This simple microscope is very serviceable in the study of botany, entomology, etc.; the durability of the lens must naturally depend upon the volatileness of the liquid used. Persons who interest themselves in observations with the microscope, especially those who desire to make researches upon this |