But it is to the Tertiary formation that these zoophytes have contributed the most enormous deposits. The greater part of the Egyptian pyramids is only an aggregation of Nummulites inserted in the syenite. A prodigious number of Foraminifera present themselves in the tertiary deposits of the Gironde, of Italy, and of Austria. The chalk so abundant in the basin of Paris is almost entirely composed of Foraminifera. The remains of these creatures are so abundant in the Paris chalk, that M. d'Orbigny found upwards of fifty-eight thousand in a small block, scarcely exceeding a cubic inch of chalk, from the quarries of Chantilly. This fact, according to this author, implies the existence of three thousand millions of these zoophytes in the cubic mètre (thirty-nine inches square and a small fraction) of rock! As the chalk from these quarries has served to build Paris, as well as the towns and villages of the neighbouring departments, it may be said that Paris, and other great centres of population which surround it, are built with the shells of these microscopic animals.
The sand of the littoral of all existing seas is so full of these minute but elegant shells, that it is often half composed of them. Ehrenberg, the celebrated German microscopist, was recently invited by the Prussian government to assist in tracing the robbery of a special case of wine. It had been repacked in littoral sand only found in an ancient sea-board in Germany. The criminal was thus detected. M. d'Orbigny found in three grammes (forty-six grains troy) of sand from the Antilles, four hundred and forty thousand shells of Foraminifera. Bianchi found in thirty grammes (four hundred and sixty-seven grains) from the Adriatic, six thousand of these shells. If we calculate the proportion of these beings contained in a cubic mètre alone of sea-sand, we reach a figure which passes all conception. What would this be if we could extend the calculation to the immensity of surface covered by the waves which surround the globe?
M. d'Orbigny has satisfied himself, by microscopic examination of sands from all parts of the globe, that it is the débris of Foraminifera which form, in all existing seas, those enormous deposits which raise banks, obstruct the navigation in gulfs and straits, and fill up ports, as may be seen in the port of Alexandria. In common with the corals and madrepores, the Foraminifera are the great agents in forming the isles which surge up under our eyes from the bosom of the ocean in the warmer regions of the globe. Thus shells, scarcely appreciable to the sight, suffice by their accumulations to fill up seas, while performing a very considerable part in the great operations of Nature, although it may not be apparent to us.
Our exact knowledge of the Foraminifera is of very recent date. Great numbers of minute particles, of regular and symmetrical form, were long distinguished on the sands of the sea shore. These corpuscular atoms early attracted the attention of observers. But with the discovery of the microscope, these small elegant shells, which were among the curiosities revealed by the instrument, assumed immense importance. We have stated that these corpuscles are nothing but the shell or solid framework of a crowd of marine animalculæ: we may then consider them as living species analogous to the Ammonites and Nautilus of geological times. Linnæus has placed them in this last genus, which would include, according to that author, all the multilocular shells. In 1804, Lamarck classed them among the molluscous cephalopods. But Alcide d'Orbigny, who has devoted long years to study and observation, and may be considered the great historian of the Foraminifera, makes it appear that this mode of classification was inexact. Dujardin separated them altogether from the class of mollusks, and showed that they ought to be consigned to an inferior class of animals. These minute creatures, in short, are deficient in the true appendages analogous to feet, which exist in the higher mollusks. They simply possess filamentous expansions, very variable in their form.
We have stated that the Foraminifera are of microscopic dimensions. With some trifling exceptions, this is generally true; but there exist a number of species which are visible to the naked eye. The Foraminifers found in the nummulite formation of Tremsted, in Bavaria, between Munich and Saltzberg, are still larger, being nearly double the size of the nummulite of the Pyramids; in short, they are the giants of this tribe of animals.
After these remarks, we may venture to give some idea of the structure and classification of these beings, whose part in the work of creation has, in former times, been so considerable.
The bodies of the Foraminifera are formed of a gelatinous substance, sometimes entire and round, sometimes divided into segments, which can be placed upon a line, simple or alternate, wound up into a spiral form or rolled round its axis, like a ball. A testaceous envelope, modelled upon the segments, follows the various modifications of form, and protects the body in all its parts. From the extremity of the last segment of one or many openings of the shell, or of the numerous pores, issue certain long and slender filaments, more or less numerous, which are divided and subdivided over their whole length, like the spreading branches of a tree. They can attach themselves to external bodies with force enough to determine the progression of the animal. Being formed of transparent non-colouring matter, they may be said to be mere expansions, which vary in form and length according to the conditions of the ambient medium. The filaments have also very variable positions: sometimes they form an unique and retractile band, issuing from a single opening; sometimes they project themselves across from numerous little pores in the shell, which covers the last segment of the animal. These pores, or openings, give the name to the creatures under consideration.
In conclusion, the filaments, contractile and variable in their form, which constitute the feet and arms of these little creatures, appear to have something electric in them: it is stated that the Infusoria are at once paralysed in their motions when brought in contact with the minute arms of the Foraminifera. "It is probably by this means," says M. Frédol, "that these creatures succeed in catching their prey. Is it not worthy of remark that these beings, however small their size and slight their form, are unpitying flesh-eaters? The smallest, the weakest, and the most microscopic animal in existence thus becomes, by means of a homœopathic dose of poison, a most formidable destroyer."
Another singular observation on these little filaments or arms we owe to Dujardin. This naturalist observed that, when a miliola attempted to climb up the walls or sides of a vase, it could improvise, as it were, on the instant, and at the expense of its own substance, a provisional foot, which stretched itself out rapidly and performed all the functions of a permanent member. The occasion served, this temporary foot seemed once more to return to the common mass, and was absorbed into the body. It would thus appear that with these minute creatures the presence of a necessity gives the power to create an organ by the mere will of the creature, while man, with all his genius, cannot manufacture a hair. To the present day, however, we have not been able to discover any organ of nutrition in the Foraminifera; they have no stomach, properly so called, but Nature has gifted them with a peculiar tissue, at once gelatinous and contractile, and essentially simulative, which probably serves the same purpose.